Austrian MBE Workshop 2017 · 2017-09-21 · Austrian MBE Workshop 2017 A1 Thermal influence of interfaces in epitaxially grown superlattices M. Grashei, G. Böhm, R. Meyer and M.-C

Austrian MBE Workshop 2017

28. - 29. September 2017

Vienna



Austrian MBE Workshop 2017Imprint

TU Wien - Technische Universität WienKarlsplatz 131040 Wienhttp://www.tuwien.ac.at/

GMe - Gesellschaft für Mikro- und NanoelektronikPräsident: Univ.Prof. Dr. Gottfried Strasserc/o TU Wien, Institut für Sensor- und Aktuatorsysteme1040 Wien, Gußhausstraße 27-29/366http://[email protected]

Organization Commitee

Scientific: Aaron Maxwell Andrews, Hermann Detz, Gottfried Strasser [email protected]

Project Management: Alexandra [email protected]. +43/(0)1/58801-36214

Institute of Solid State Electronics E362Floragasse 7 / Gußhausstraße 25a1040 Wien, Austriahttps://fke.tuwien.ac.at/

Tel. +43/(0)1/58801-36201Fax +43/(0)1/58801-36299

Cover pictures are copyrighted from TU Wien, H. Detz & A. M. Andrews.


5Austrian MBE Workshop 2017

Index

Preface ............................................................................................................7

Workshop Program .........................................................................................8

Poster Session Overview ...............................................................................11

Oral Presentations Abstracts ........................................................................13

Poster Presentations Abstracts .....................................................................43

List of Exhibitors ............................................................................................75

List of Participants ........................................................................................76

Workshop Venue ..........................................................................................79

Public Transport ............................................................................................80

Workshop Dinner ..........................................................................................81

Vienna Sights ................................................................................................82



Preface

Dear MBE colleagues,

We welcome you to this year‘s “German” MBE Workshop in Vienna, Austria.

This meeting provides an open platform for scientific and technological exchange regarding

all aspects of molecular beam epitaxy. The list of abstracts resembles this broad field

and includes basic science, theoretical models, growth processes, advances of ultra-high

vacuum equipment, and functional state-of-the-art devices.

We would like to thank the over 100 authors and participants for their valuable high quality

contributions, submitted from ten different countries, which are compiled into a two-day

program of 24 oral and 25 poster presentations.

We hope that the heart of Vienna with its rich cultural variety, historical buildings, and

motivated participants provides a stimulating environment for scientific discussions and

social interaction. We wish you productive, pleasant, and memorable days in Vienna!

The MBE 2017 Workshop organizing team:

Aaron Maxwell Andrews, Hermann Detz,

Alexandra Linster and Gottfried Strasser


Workshop ProgramThursday

09:00 Exhibitors Setup

11:00 Registration & Exhibitors

11:45 Lunch & Coffee

12:45 Welcome

13:00 A1: M. Grashei "Thermal influence of interfaces in epitaxially grown superlattices"

13:15 A2: T. Tschirky "Scattering mechanisms of highest-mobility InAs/AlxGa1-xSb quantum wells"

13:30 A3: C. Deneke "Overgrowth study of back-bonded III-V semiconductor membranes"

13:45 A4: L. Prochaska "Epitaxial YbRh2Si2 films grown by molecular beam epitaxy"

14:00 A5: A. Pawlis "Strain Compensation in ZnSe/CdSe Quantum Wells"

14:15 A6: M.P. Semtsiv "Growth... of Rhodium-doped InGaAs & InP by gas-source MBE"

14:30 Coffee

15:00 Group Photo

15:30 B1: J.-M. Chauveau "...Polar, Nonpolar and semipolar (Zn,Mg)O/ZnO...UV & THz applications"

15:45 B2: E. Hildebrandt "Control of Switching Modes & Conductance Quantization"

16:00 B3: R. Delgado "Towards GaN integration on Si: Microstructural study of ScN…on Si(111)"

16:15 B4: G. Calabrese: "MBE of GaN nanowires on flexible metal folls: challenges and prospects"

16:30 B5: S. Breuer "...Photoconductive THz Emitters & Detectors made of Fe-doped InGaAs"

16:45 B6: V.V. Volobuev "...Band Structure of PbSn Chalcogenide Topological Crystalline Insulators"

17:00 Poster Session

18:30 Bus 1 & 2 to Dinner

19:00 Dinner - Martin Sepp

21:30 Bus 1 back to Workshop Location

22:00 Bus 2 back to Workshop Location


Friday

09:00 C1: E. Dimakis "GaAs-based core/shell nanowires ... grown on Si substrates"

09:15 C2: M.I. Lepsa "Self-catalyzed grown InAs/GaSb core-shell nanowire arrays"

09:30 C3: D. Ruhstorfer "Selective Area Epitaxy & Doping of Catalyst-Free GaAs Nanowires ..."

09:45 C4: T. Pejchal "...Ge nanowires: The co-effect of atomic hydrogen & catalyst spreading"

10:00 C5: E. T. Papaioannou "…Fe/Pt bilayers in optimizing the spin-pumping induced...emission"

10:15 C6: S. Gaucher "Magnetic Properties of Ferromagnet/Semiconductor/Ferromagnet..."

10:30 Coffee

11:00 D1: X. Y. Yuan "New Optical selection rules from GaAs quantum dots...stress actuators"

11:15 D2: H. Huang "Novel quantum optical devices based on doplet epitaxial GaAs/AlGaAs..."

11:30 D3: R. Keil "Solid-state ensemble of highly entangled photon sources at rubidium atomic …"

11:45 D4: H. Groiss "Phase separation in metastable Ge1-xSnx epilayers induced by...Sn precipitates"

12:00 D5: J. Falta "Initial growth of tin on silicon & germanium surfaces"

12:15 D6: J. Schmidt "Carbon-mediated epitaxy of SiGe virtual substrates on Si(001)"

12:30 Lunch & Coffee

13:30 Closing Remarks & Open Discussion

13:45



Poster Session OverviewP1: F. Lange “Growth of Si, Ge, and SiGe Nanowires”

P2: C. Reichl “Manipulating the Wavefunction of High-Quality 2DEGs in GaAs/AlGaAs using Advanced Gating Techniques”

P3: J. Scharnetzky “Patterned Back Gates suitable for Ultra-High Quality GaAs/AlGaAs Heterostructure Epitaxy”

P4: T. Musalek “Preparation of bimetallic catalysts for nanowire growth”

P5: D. Reuter “Site-controlled Ga droplet epitaxy by deposition through shadow masks”

P6: S.F.C. da Silva “Growth & characterization of unstrained GaAs/AlGaAs quantum dots”

P7: J. Straßner “Growth control with RAS of highly ordered Ga(As)Sb quantum dots grown on pre-structured GaAs”

P8: W. Braun “Beating 1/r²: cylindrical crucibles for large working distances”

P9: D. K. Polyushkin “CVD growth of atomically thin MoS2 films for digital electronics”

P10: R. Szedlak “Ring Quantum Cascade Lasers: Versatile Light Emission and Applications in Spectroscopic Sensing”

P11: S. Lancaster “Influence of boron incorporation in GaAs nanowires grown by self-catalysed MBE”

P12: M. Beiser “Bi-functional Quantum Cascade Detectors/Lasers”

P13: M. Holzbauer “The polarization of ring interband cascade lasers”

P14: A. Harrer “Quantum Cascade Detector Pixel”

P15: M. Kainz “Asymmetry study for high performance InGaAs/InAlAs terahertz quantum cascade lasers”

P16: S. Schönhuber “High Power THz Quantum Cascade Lasers”

P17: B. Limbacher “Inverse Bandstructure Engineering of Alternative Barrier Materials for InGaAs-based Terahertz Quantum Cascade Lasers”

P18: Z. Bao “Understanding layers, nanowires & nanodots better on a lab multipurpose diffractometer”

P19: X. Zhang “Fabrication of quasi-Gaussian-shaped nanoholes by MBE local droplet etching”

P20: J. Hofinger “Pulsed laser deposition of In2O3 thin films on YSZ(111)”

P21: A. Elsayed “Characterization of thin Boron layers grown on Silicon utilizing Molecular Beam Epitaxy for ultra-shallow pn-junctions”

P22: P. Lackner “Wetting and dewetting of metals by sputter-deposited zirconia”

P23: D. Schwarz “Growth of SixGe1-x-ySny Structures with High Sn Content for Bandgap Investigation”

P24: B. Hinkov “Fabrication of ZnO-based Resonant Tunneling Diodes for Quantum Cascade Structures “

P25: S. Wimmer “Natural Superlattice Structures of Bi-Chalcogenide Topological Insulators grown by MBE and Controlled by Stoichiometry”



Oral Presentations

Abstracts



A1

Thermal influence of interfaces in epitaxially grown superlattices

M. Grashei, G. Böhm, R. Meyer and M.-C. Amann

Walter Schottky Institut, Am Coulombwall 4, Germany

Today, a large variety of epitaxially grown opto-electronic devices exists, which have to fulfill several requirements according to their operating conditions. Opto-electronic devices are often limited by the operation temperature and an optimized thermal design is necessary to achieve maximum performance. For instance, heat removal in a vertical cavity surface emitting laser (VCSEL) is limited by the thermal conductivity of the cavity and the distributed Bragg reflector (DBR). Especially in an upside-up design, the DBR limits the heat removal, since the superlattice (SL) often contains ternary and even quartenary materials of varying, but usually very low, thermal conductivities and corresponding interfaces between these materials. Whereas the thermal conductivities of the bulk-materials are usually well known, the influence of interfaces remains often unclear or is neglected.

Here, we present an investigation of the interface influence on the thermal properties of epitaxially grown superlattices. For determination of the thermal properties we employed the 3-ω-method which was introduced by D. Cahill in 19871 and is widely used for film-on-substrate thermal characterization (see Fig 1. Inset). The principle is based on the excitation of thermal waves, which penetrate into the sample. From the temperature rise in the heater stripe the thermal properties can be calculated. A set of samples with constant total film thickness dF but varying number n from 1 to 512 of GaAs/AlAs-superlattice pairs of equal layer thickness was grown with a Varian Gen II MBE-system. Platinum stripes were photolithographically fabricated on top of the samples for harmonic Joule heating. By measuring the temperature rise in the heater for each sample we can determine the different thermal resistances of the samples with varying number of SL-pairs.

We can attribute these differences directly to the thermal resistance of the interfaces, since the overall thickness of the superlattice is kept constant. In addition, we verified our results via heat transfer simulations in Comsol Multiphysics and compared them to additionally measured data from a ternary Al0.5Ga0.5As film. By accurate thermal modeling of the entire multilayer structures, knowledge for further thermal design of opto-electronic devices and related epitaxial growth of multilayer-structures can be gained. From Fig. 1 we identify good agreement between experiment and simulation together with a linear increase of the total SL-thermal resistance as a function of the interface number, which is a superposition of additional one-dimensional thermal interface resistances and two-dimensional heat spreading effects in the multilayer structure.

[1] David G. Cahill, R. O. Pohl, Phys. Rev. B, 35, 4068-4073 (1987). *Contact [email protected] [email protected]

Fig. 1: The thermal resistance of a superlattice increases linearly with number of the interfaces. Reference values of bulk film are plotted as dashed lines. Inset: Thermal waves, excited by an oscillating current in the heater stripe, penetrate into the epitaxial superlattice to determine the influence of interfaces on the thermal conductance.

dF


A2

Scattering mechanisms of highest-mobility InAs/AlxGa1-xSb quantum wells

T. Tschirky 1,*, S. Mueller 1, Ch. A. Lehner 1, S. Fält 1, T. Ihn 1, K. Ensslin 1

and W. Wegscheider 1

1 Laboratory for Solid State Physics, ETH Zürich, 8093 Zürich, Switzerland

Heterostructures containing InAs are commonly studied due to their potential applications in high-speed, low power-electronics, such as in heterostructure field effect transistors (HFETs) and THz imaging and sensing. The large band offset between InAs and the AlSb barriers results in excellent carrier confinement and enhanced radiation tolerance. Its narrow band gap and strong spin-orbit coupling makes the system ideal for spintronic devices research. In recent years research on InAs quantum wells has gained significance due to their similarity to InAs/GaSb composite quantum wells for topological insulators [1] and due to new prospects for realizing a topological superconducting phase supporting Majorana fermions when combined with s-wave superconductors [2,3,4].

The carrier mobility of InAs quantum wells [5,6,7,8] has for a long time been confined to regions below 1 x 106 cm2/Vs, whereas GaAs/AlGaAs heterostructures can reach mobility values above 3 x 107 cm2/Vs [15,16,17,18] despite their higher effective mass. This implies that there is ample room for improving the growth techniques and structure designs of InAs quantum wells.

The recent availability of high quality, almost lattice-matched GaSb substrates has led to a considerable increase of growth quality and the subsequent carrier mobilities [7]. In this work, we show that by further optimizing structural design parameters, the mobility can be drastically increased. The highest electron mobilities were achieved with Al0.33Ga0.67Sb buffers and lower barriers and a quantum well width of 24 nm. These quasi-single-interface InAs/AlSb quantum well devices reached a gate-tuned mobility of 2.4 x 106 cm2/Vs at a density of 1 x 1012 cm-2 at 1.3 K.

In Hall bar devices boundary scattering is found to strongly influence the mobility determination in this mobility regime. Using

temperature and density dependent magnetotransport measurements, ionized background impurity scattering at low electron densities, device boundary scattering at intermediate electron densities, and intersubband scattering at high electron densities were identified as the most dominant scattering processes. Ringlike structures appearing in the Landau fan at high electron densities are explained using a single-particle model of crossing Landau levels. [1] C. Liu et al.,Phys. Rev. Lett., 100, 236601 (2008). [2] J. D. Sau et al, Phys. Rev. Lett., 104, 040502 (2010). [3] J. Alicea, Phys. Rev. B, 81, 125318 (2010). [4] R. M. Lutchyn et al, Phys. Rev. Lett., 105, 077001 (2010). [5] C. Nguyen, Ph.D. thesis, University of California at Santa Barbara (1993). [6] M. Thomas et al, Journal of Crystal Growth 175-176, 894 (1997). [7] B. Shojaei et al, Applied Physics Letters, 106, 222101 (2015). [8] B. Shojaei et al, Phys. Rev. B, 94, 245306 (2016). [9] S. Riedi et al, Journal of Crystal Growth, 455, 37 (2016). [10] G. C. Gardner et al, Nat Mater, 9, 881 (2010). [12] V. Umansky et al, Journal of Crystal Growth, 311, 1658 (2009). *Contact: [email protected]

Fig. 1: Measured electron mobilities at 1.3 K of an InAs QW with varying Hall bar widths.


A3

Overgrowth study of back-bonded III-V semiconductor membranes

J. Garcia Jr.1, L. do Nascimento Rodrigues1, S.Filipe Covre da Silva1,2, O. D.

D. Couto Jr.4, F. Iikawa4, S. L. Morelhao3 and Ch. Deneke1,4,*

1Laboratório Nacional de Nanotecnologia (LNNano), Campinas, SP, Brasil 2Departamento de Física, Universidade Federal de Viçosa (UFV), Viçosa, MG, Brasil

3Departamento de Física Aplicada, Universidade Estadual de São Paulo (USP), São Paulo, Brazil

4Instituto de Física "Gleb Wataghin", Universidade Estadual de Campinas (UNICAMP), SP, Campinas Brazil

In the last decade, freestanding semi-

conductor nanomembranes have been established as promising novel class of two-dimensional semiconductor structures. Such structures have been used to form hybrid nanomaterials, constructing devices for optical applications as well as flexible electronics.

In this work, we investigate the over-growth behavior of a virtual substrate based on a completely released, wrinkled and in-place bonded GaAs/InGaAs/GaAs mem-branes. The virtual substrate was obtained by molecular beam epitaxy (MBE) growth of the heterostructure on an AlAs sacrificial layer over a GaAs (001) substrate. In a second fabrication step, the heterostructure structure is release by selectively removing the AlAs sacrificial layer, cleaned and re-introduced into the MBE, where it serves as template for growth. After atomic hydrogen cleaning, we deposited 10-nm thick InxGa1-

xAs layers varying the Indium content from x=0.05 to x=1.

Samples are characterized using atomic force microscopy, scanning electron micros-copy, 3D reciprocal space mapping obtained by gracing incident x-ray diffraction and photoluminescence measurements.

Results from microscopy show a flat InGaAs layer growth up to x=0.4 on the membranes, whereas layers on GaAs al-ready show island and dislocation formation at x>0.3. Furthermore, we observe the formation of bubbles in the membrane for higher Indium content as well as preferred material migration and accumulation on top of wrinkles. The shift in the critical thickness for island formation is associate to the change in the lattice parameter of virtual substrate compared to bulk GaAs. Furthermore, the membrane acts as

compliant substrates This assumption is strongly supported by the x-ray diffraction experiments indicating coherent crystal growth up to x=0.4.

To demonstrate the ability to grow optical or electric active structures on membranes, we deposited a nominally unstrained InAlGaAs/InGaAs/InAlGaAs quantum well on top of a released wrinkled membrane. From the observed red shift photo-luminescence signal (see Fig. 1) from this quantum well compared to a reference grown on GaAs (001) wafers, we conclude that the quantum well on the membrane is less or not strained compared to structures grown on bulk GaAs substrates.

*Contact: [email protected]

Fig. 1: Photoluminescence spectrum obtained from an InAlGaAs/InGaAs/InAlGaAs quantum well grown on a released and relaxed membrane or a GaAs (001) substrate as reference. The upper inset shows the AFM topography of the quantum well on the membrane, the lower the grown structure.


A4

Epitaxial YbRh2Si2 films grown by molecular beam epitaxy

L. Prochaska 1*, D. MacFarland 2, A. M. Andrews 2, M. Bonta 3, H. Detz 4,5, W. Schrenk 4, E. Bianco 6, G. Strasser 2,4, A. Limbeck 3, E. Ringe 6,

and S. Paschen 1

1 Institute of Solid State Physics, TU Wien, 1040 Vienna, Austria 2 Institute of Solid State Electronics, TU Wien, 1040 Vienna, Austria

3 Institute of Chemical Technologies and Analytics, TU Wien, 1040 Vienna, Austria 4 Center for Micro- and Nanostructures, TU Wien, 1040 Vienna, Austria

5 Austrian Academy of Sciences, 1010 Vienna, Austria 6 Department of Materials Science and Nanoengineering, Rice University, Houston,

Texas 77005, USA

Quantum criticality is in the focus of studies of strongly correlated electron materials. Due to their small and competing energy scales, heavy fermion compounds have played a key role in this research. YbRh2Si2 is a prototypal quantum critical heavy fermion metal that exhibits a Kondo destruction quantum critical point as its antiferromagnetic phase is fully suppressed by the application of a small magnetic field [1,2,3]. By studying the cubic compound Ce3Pd20Si6 it was realized that dimensionality is an efficient way to tune through the theoretically suggested [4,5] global phase diagram for antiferromagnetic heavy fermion compounds [6]. Thus, it would be of great interest to tune YbRh2Si2 towards the extreme 2-dimensional limit. The successful molecular beam epitaxy (MBE) growth of single crystalline thin films of YbRh2Si2 would provide the unique ability to achieve such tuning. Recent results for CeIn3/LaIn3 [7], CeCoIn5/YbCoIn5 [8] and CeRhIn5/YbRhIn5 [9] superlattices are encouraging and validate our approach.

We have set up an MBE system equipped with a low-temperature evaporation cell for ytterbium and two electron beam evaporators for rhodium and silicon. The YbRh2Si2 films are grown on germanium substrates due to the low lattice mismatch. The rhodium flux determines the maximum growth rate in our system. We found working growth conditions for YbRh2Si2 and verified the grown film to have the correct phase by transmission electron microscopy (TEM) diffraction and atomic resolution images (Fig. 1). The chemical characterization was performed by inductively coupled plasma optical emission

spectroscopy (ICP-OES) and cross-checked against several other analytical techniques. In addition, electrical resistivity measure-ments are used to benchmark the film quality.

Fig. 1: High resolution TEM image.

We acknowledge financial support by the

European Research Council (ERC Advanced Grant No. 227378), the Austrian Science Fund (FWF Doctoral School Solids4Fun W1243) and the U.S. Army research office (Grant W011NF-14-1-0497).

[1] S. Paschen et al., Nature 432, 881 (2004) [2] S. Friedemann et al., PNAS 107, 14547

(2010) [3] Q. Si and S. Paschen, Phys. Status Solidi

B 250, 425 (2013) [4] Q. Si, Physica B 378, 23 (2006) [5] Q. Si, Nature 493, 619 (2013) [6] J. Custers, et al., Nature Mater. 11, 189

(2012) [7] H. Shishido, et al., Science 327, 980

(2010) [8] Y. Mizukami, et al., Nature Phys. 7, 849

(2011) [9] T. Ishii et al., Phys. Rev. Lett. 116, 206401

(2016) *Contact: [email protected]


A5

Strain Compensation in ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence

T. Rieger 1, T. Riedl 2, J.K.N Lindner 2, D. Grützmacher 1and A. Pawlis 1,*

1 Peter Grünberg Institute 9 and JARA-FIT, Forschungszentrum Jülich GmbH, Wilhelm Johnen

Strasse, 52425 Jülich, Germany 2 Department of Physics, University of Paderborn, Warburger Strasse 100, 33098 Paderborn,

Germany

Optically active devices based on ZnSe/CdSe heterostructures are in principle capable to provide light emission over the whole visible spectrum via a variation of the dimensions. However, the lattice mismatch between ZnSe and CdSe of about 7 % limits the thickness of coherently grown CdSe layers on ZnSe to ~2 monolayers (MLs). Between 2 and 3 MLs CdSe, Stranski-Krastanov quantum dots develop and after-wards plastic relaxation takes place for CdSe thicknesses exceeding 3 MLs. This leads to quenching of the emission via dominant non-radiative recombination in the devices [1]. In a recent publication, we observed efficient light emission from ZnSe/CdSe/ZnSe quantum well (QW) structures with CdSe thicknesses up to 6 MLs [2]. The latter was achieved with a dedicated strain compensation technique involving In0.12Ga0.88As pseudo-substrates that induce alternatingly strained ZnSe and CdSe layers. Due to the alternating strain in the ZnSe and CdSe, the strain of the entire ZnSe/CdSe/ZnSe stack is compensated with respect to the In0.12Ga0.88As buffer.

Here, we present a study of the strain compensation by transmission electron microscopy (TEM) and compare experi-mentally determined strain profiles to simulated ones [3]. Moreover, we demon-strate that ZnSe/CdSe/ZnSe QWs with CdSe thicknesses up to 5 MLs grow fully coherent due to the dedicated strain compensation technique. Finally, we introduce a simple model approach to tailor a variable sample structure towards efficient strain compensation. This model approximation is sufficiently general and valid to be applied to other highly mismatched epitaxial systems and paves the way for novel designs of advanced strain compensated heterostructures.

[1] M. Strassburg, T. Deniozou, A. Hoffmann, R. Heitz, U. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, S. Schwedhelm, K. Lischka, D. Schikora, Appl. Phys. Lett. 76, 685 (2000). [2] A. Finke, M. Ruth, S. Scholz, A. Ludwig, A. Wieck, A., D. Reuter, A. Pawlis, Phys. Rev. B 91, 035409 (2015). [3] T. Rieger, T. Riedl, E. Neumann, D. Grützmacher, J. K. N. Lindner, A. Pawlis, ACS Appl. Mat. Int. 9, 8371-8377 (2017). *Contact: [email protected]

Fig. 1: Upper part: Sample structure and layer sequence of a typical ZnSe/CdSe/ZnSe strain compensated QW. Lower part: TEM image of the CdSe QW region with superimposed strain distribution along the growth direction.


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A6

Growth and characterization of Rhodium-doped InGaAs and InP by gas-source MBE

M.P. Semtsiv 1*, R.B. Kohlhaas 2, S. Breuer 2, B. Globisch 2, M. Schell 2

and W.T. Masselink 1

1 Physics Department, Humboldt University Berlin, Newtonstrasse 15, 12489 Berlin

2 Fraunhofer Heinrich Hertz Institute for Telecommunications HHI, Einsteinufer 37, 10587 Berlin

Intentional doping of epitaxial

semiconductor layers with deep acceptors is crucial for several device applications, such as buried-heterostructure lasers [1] and photoconductive THz emitters and receivers [2]. Iron is the most common and well studied deep acceptor for InP and In0.53Ga0.47As and has been used as a dopant in solid-source MBE, in gas-source MBE, and in MOVPE epitaxial methods. On the other hand, iron is known to cluster at high doping concentrations, to diffuse into adjacent layers, and to build interstitial defects under certain growth conditions.

Early studies of MOVPE grown InP and In0.53Ga0.47As consider further transition-metal dopants as possible alternatives to Fe, such as Ru, Rh, Ti, and Ir [3]. These materials did show significantly lower diffusion and superior electrical compensation properties. Contrary to Fe with atomic covalent radius of 0.152 nm, Ru, Rh, and Ir have atomic covalent radius of 0.142 nm, which is identical with covalent radius of Indium. This coincidence implies a minimal crystal cell deformation around the dopant in InP. All three – Ru, Rh, and Ir – are inert noble metals, which excludes the possibility of the source contamination via arsine, phosphine, and /or oxygen. Out of these three potential dopants, Rh has the highest vapor pressure and is therefore more straightforward to use in MBE using conventional thermal evaporation cells.

In this paper we describe the properties of Rh-doped InP and In0.53Ga0.47As grown on InP substrates by gas-source MBE. 4N-purity Rh was evaporated using conventional high-temperature doping cell with pyrolytic-graphite crucible at temperatures between 1300°C and 1800°C. We demonstrate residual carrier density

concentrations down to 2×1012 cm-3 at room temperature, and electron-hole

recombination times in In0.53Ga0.47As:Rh down to 0.1 ps. These results open up a potential of using the MBE-grown In0.53Ga0.47As:Rh on InP as an absorber material in future commercial photoconductive THz emitters and receivers.

Fig. 1. Electron-hole recombination time

measured in In0.53Ga0.47As:Rh as a function of Rh-cell temperature.

This research was supported by the

German Research Society (DFG) and the Mid-TECH Project of EU Horizon 2020 Program, Grant Agreement No.642661.

[1] M.P. Semtsiv, A. Aleksandrova, M. Elagin, G. Monastyrskyi, J.-F. Kischkat, Y.V. Flores, W.T. Masselink, J. Cryst. Growth, 378, 125 (2013). Y.V.Flores, M.Elagin, S.S.Kurlov, A.Aleksandrova, G.Monastyrskyi, J.Kischkat, M.P.Semtsiv, W.T.Masselink, J. Cryst. Growth, 398, 40 (2014). [2] B Globisch, R.J.B. Dietz, R.B. Kohlhaas, T. Göbel, M. Schell, D. Alcer, M. Semtsiv, W.T. Masselink, J. Appl. Phys., 121, 053102 (2017). [3] B. Srocka, H. Scheffler, and D. Bimberg, Appl. Phys. Lett. 64, 2679 (1994). A. Dadgar, O. Stenzel, A. Näser, M. Zafar Iqbal, D. Bimberg, and H. Schumann, Appl. Phys. Lett. 73, 3878 (1998). *Contact: [email protected]

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B1

MBE Growth of Polar, Nonpolar and semipolar (Zn,Mg)O/ZnO for potential UV and THz applications

J.-M. Chauveau 1*, M. Hugues1, N. Le Biavan1, D. Lefebvre1, B. Damilano1, B.

Vinter1, M. Montes Bajo2, J. Tamayo-Arriola2, A. Hierro2

1 Université Cote d’Azur, CNRS, CRHEA, 06560 Sophia Antipolis, France 2 ISOM - The Institute of Optoelectronics Systems and Microtechnology, ETSI de Telecomunicación,

Universidad Complutense de Madrid, ,28040 Madrid, Spain

ZnMgO/ZnO Quantum well heterostructures (QW) have attracted much attention due to their opportunity of combining band gap engineering, with large excitonic binding energies. So far, studies on ZnO have mainly focused on films grown on c-(0001) plane. Unfortunately, the wurtzite ZnO layers exhibit built-in electric fields along the c-axis, affecting the electronic properties. In this presentation, we will demonstrate that the non-polar surfaces are an alternative route for the fabrication of wide QWs with no reduction of the exciton binding energies. This property is first demonstrated in QWs grown on sapphire. Then we show a drastic improvement of the structural properties when the QWs are grown on ZnO substrates: no residual strain, smooth interfaces, no extended defects, reduced surface roughness, reduced X-Ray full width at half maximum. A strong enhancement of the photoluminescence (PL) properties is also demonstrated compared to heteroepitaxial QWs and the integrated PL intensity can be constant as a function of the temperature up to RT after optimization. Light emitting devices were then fabricated with these active layers. The structural quality does not deteriorate even after the growth of the n-type and nitrogen doped ZnMgO layers as “p-type” layer. The devices exhibit a clear rectifying behavior. Under forward bias a clear emission from the 4nm QWs is observed at 373nm, close to the QW PL (371nm). However the outpower is still very poor due to the lack of efficient p-type doping.

In order to avoid the limitation of the p-type doping, we propose and demonstrate the potential of the nonpolar ZnO/(Zn,Mg)O material system as a candidate for intersubband (ISB) devices, which do not

require p-type layers. This material system presents a unique set of properties that makes it highly attractive for mid-IR and THz emission as well as for strong coupling regimes: (1) it can be doped up to 1021 cm-3, (2) it has a very large longitudinal phonon energy of 72 meV, (3) it is very ionic with a large difference between the static and high frequency dielectric constants. After optimization, the QW interface roughness is in the range of a few Å without defect or strong composition fluctuations. The doping level is then optimized to reach n~5x1020 cm-3 in ZnO (n above 5x1013 cm-2 in our QWs). Thanks to the careful optimization of the growth conditions, ISBT are observe for the first time in nonpolar ZnO-based heterostructures

This “Zoterac” project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 665107”. *Contact: [email protected]

2000 3000

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Fig. 1: p to s polarization absorbance ratio for the MQW structures presented here for (a) different QW widths (b) different -type doping.


B2

Fig. 1: A schematic qualitative model of switching modes in Pt/m-HfO2/TiN (depicted by M1-M4) and Pt/t-HfO1.5/TiN (T1-T4). In the m-HfO2 stack, the transition M1 M2 corresponds to cf8-bipolar resistive switching (BRS); the transition M3 M4 corresponds to unipolar resistive switching (URS), and M3 M4 M3 to threshold resistive switching (TRS). In the t-HfOx stack, cf8-BRS is shown as T1 T3, f8- BRS as T1 T2 and complementary resistive switching as T4 T1 T2.

Control of Switching Modes and Conductance Quantization in Oxygen Engineered HfOx based Memristive Devices

S. U. Sharath1, S. Vogel1, L. Molina-Luna1, E. Hildebrandt1, C. Wenger2, J.

Kurian1, M. Duerrschnabel1, T. Niermann3, G. Niu4, P. Calka2, M. Lehmann3, H.-J. Kleebe1, T. Schroeder2, 5, and L. Alff1*

1 Technische Universität Darmstadt, Alarich-Weiss-Str. 2, 64287 Darmstadt, Germany

2 IHP GmbH, Im Technologiepark 25, 15236 Frankfurt Oder, Germany 3Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany

4Xi'an Jiaotong University, 710049 Xi'an, China 5Brandenburgische Technische Universität, Konrad-Zuse-Str. 1, 03046 Cottbus, Germany

Hafnium oxide (HfOx) based memristive devices have tremendous potential as non-volatile resistive random access memory (RRAM) and in neuromorphic electronics. Despite its seemingly simple two-terminal structure, myriad of RRAM devices reported in the rapidly growing literature exhibit rather complex resistive switching behaviors.

Using Pt/HfOx/TiN based metal-insulator-metal structures as model systems, we show that, a well-controlled oxygen stoichiometry governs the filament formation and the occurrence of multiple switching modes. [1] The oxygen vacancy concentration is found to be the key factor in manipulating the balance between electric field and Joule heating during formation, rupture (reset), and reformation (set) of the conductive filaments in the dielectric. In addition, the engineering of oxygen vacancies stabilizes atomic size filament constrictions exhibiting integer and half-integer conductance quantization at room-temperature during set and reset. Identifying the materials conditions of different switching modes and

conductance quantization contributes to a unified switching model correlating structural and functional properties of RRAM materials.

The possibility to engineer oxygen stoichiometry in HfOx will allow creating quantum point contacts with multiple conductance quanta as a first step towards multi-level memristive quantum devices. [1] S. U. Sharath, S. Vogel, L. Molina-Luna, E. Hilde-brandt, C. Wenger, J. Kurian, M. Duerrschnabel, T. Niermann, G. Niu, P. Calka, M. Lehmann, H.-J. Klee-be, T. Schroeder, and L. Alff, Adv. Func. Mat., accept-ed *Contact: [email protected]


B3

Towards GaN integration on Si: Microstructural study of ScN grown on Si(111) by plasma-assisted MBE for applications as a buffer layer

R. Delgado1*, M.H. Zoellner 1, P. Sana1, H. Tetzner1, P. Zaumseil1, J. Dabrowski1,

M.A Schubert1 and T. Schroeder1,2

1 IHP GmbH, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany 2 BTU Cottbus Senftenberg, Institute of Physics and Chemistry, Konrad Zuse Str.1, 03046 Cottbus,

Germany

GaN is a promising semiconductor material which has attracted significant attention last decades due to its interesting properties for future device applications. In that regard, the integration of high quality GaN on Si is currently an important research area. The growth of GaN directly on Si is very difficult due to the high lattice mismatch (-17%), thermal mismatch (56%) and the reactive interface. To reduce these effects and suppress chemical reactions, ScN has been proposed as a buffer layer, since it exhibits only 0.1% lattice mismatch with GaN [1]. ScN is a transition metal nitride semiconductor. Its rock-salt structure featuring a compatible atomic arrangement in the [111] surface orientation as the wurtzite GaN structure in the [0001] orientation [2]. The huge lattice mismatch between ScN and Si (-17%) makes their epitaxial integration difficult. In previous studies, ScN has been integrated on Si using a step-graded buffer layer composed of two different oxides, Sc2O3 and Y2O3 [3]. Moram et al. have demonstrated the possibility to obtain epitaxial type-B oriented ScN directly on Si by NH3-plasma assisted MBE [4]. However, the presence of twins might be a limiting feature for subsequent growth of high quality GaN films.

In this study, thin ScN films were grown by plasma-assisted molecular beam epitaxy with a thickness ranging from 8 to 19 nm on Si (111) oriented substrates. The structural quality of the epi-layers has been investigated as a function of the thickness by XRD (X-ray diffraction), TEM (Transmission electron microscopy) and AFM (Atomic force microscopy). XRD in specular configuration confirms that the ScN epi-layers are (111) oriented and ϕ-scans show true single-crystallinity for the samples

with thicknesses in the range from 8 to 17 nm. Cross-sectional TEM studies confirm the type-A oriented ScN films with respect to the substrate (Figure 1). Despite the single-crystalline nature and the lack of twin inclusions, ω rocking curves and ϕ-scans reveal tilt and twist, respectively. The morphology of the surface has been visualized by AFM showing a flat and smooth ScN surface up to 19nm thickness.

First attempts to grow GaN by PA-MBE on ScN(111)/Si(111) resulted in a single-crystalline epitaxial film which is confirmed by specular ω-2θ and azimuthal ϕ-scans determining the epitaxial relationship: GaN(0001)/ScN(111)/Si(111) and GaN[10-10] ‖ScN[1-10]‖Si[1-10] .

[1] M.A. Moram et al., Applied Surface Science 252 8385-8387 (2006) [2] Kappers et al, Physica B 401-402, 296-301 (2007) [3] Lupina et al, Appl. Phys. Lett. 107, 201907 (2015) [4] M.A. Moram et al., J. Appl. Phys. 100, 023514 (2006) *Contact: [email protected]

Si(111)

IF

ScN(111)[-111]

[-111]

Figure 1: HRTEM image of ScN 8nm thick. The normal directions to the (-111) planes are indicated by white arrows.


B4

Molecular beam epitaxy of GaN nanowires on flexible metal foils: challenges and

G. Calabrese 1,*, C. Pfüller

A. Trampert1, J. K. Grepstad

1 Paul-Drude-Institut f

2 Department of Electronic Systems, NTNU

The integration of electronic and

optoelectronic devices on flexible substrates is motivated by the promise of novel and/or economically relevant applications. In this context, inorganic semiconductor nanowires have recently emerged as promising candidates for flexible electronics and optoelectronics. Metal foils represent a particularly interesting type of substrate for nanowire growth because they are not only flexible but also exhibit excellent electrical and thermal conductivities as well as a high optical reflectance. In addition, the use of polycrystalline and large area metal foils as substrates might also lead to an increased throughput and a significant cost reduction

In this work, we discusschallenges towards the integration of GaN nanowires (GaN being the material of choice for solid-state lighting and high power electronics) on bare Ti foils as well as on Ni foils covered with a multilayer graphene film. We demonstrateoptimized growth conditions GaN nanowires on Ti foils have structural and optical properties that are comparable to those of GaN nanowires grown on conventional substrates like Si. We also show that material system is stable against substrate bending1.

Randomly oriented, uniformly tilted, and vertically aligned GaN nanowires can be grown on Ti foils depending on the crystallinity of the native oxide as well as on the in-situ treatments of the foil surface before nanowire growth (cf. Fig. 1)growth of vertically oriented GaN on polycrystalline Ti foils is found to require the presence of an amorphous surfaceoxide layer, which is effective in interrupting the epitaxial relation between the grains in the foil and the nanowires. An alternative

Molecular beam epitaxy of GaN nanowires on flexible metal foils: challenges and prospects

C. Pfüller1, P. Corfdir1, S. V. Pettersen2, G. Gao1,

, J. K. Grepstad2, O. Brandt1, L. Geelhaar1, S. Fern

Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin,Germany

Department of Electronic Systems, NTNU—Norwegian University of Science andTechnology, Trondheim 7491, Norway

The integration of electronic and optoelectronic devices on flexible substrates

of novel and/or economically relevant applications. In this context, inorganic semiconductor nanowires have recently emerged as promising

for flexible electronics and Metal foils represent a

particularly interesting type of substrate for nanowire growth because they are not only

but also exhibit excellent electrical and thermal conductivities as well as a high optical reflectance. In addition, the use of

ystalline and large area metal foils as substrates might also lead to an increased throughput and a significant cost reduction.

discuss the main challenges towards the integration of GaN nanowires (GaN being the material of

state lighting and high bare Ti foils as well as

on Ni foils covered with a multilayer demonstrate that under

optimized growth conditions GaN nanowires on Ti foils have structural and optical

omparable to those of conventional rigid

show that this material system is stable against substrate

andomly oriented, uniformly tilted, and vertically aligned GaN nanowires can be

on Ti foils depending on the crystallinity of the native oxide as well as on

of the foil surface (cf. Fig. 1). The

GaN nanowires on polycrystalline Ti foils is found to require

an amorphous surface , which is effective in interrupting

the epitaxial relation between the grains in the foil and the nanowires. An alternative

approach for the achievement of nearly vertically oriented GaN nanowires on a flexible and polycrystalline metal foilconsists in the introduction of a multilayer graphene film at the Multilayer graphene is found to efficiently interrupt the epitaxial relation between the growing GaN nanowires and the grains in the foils without the detrimental insulating amorphous oxide layer. Obtained results represent a first important step towards the fabrication of flexible GaN-nanowire based devices on metal foils.

Fig. 1: Scanning electron micrographs showing self-assembled GaN nanowires on a Ti foil covered by a crystalline (a)

amorphous native oxide (c)

growth, respectively.

[1] G. Calabrese, P. Corfdir, G.Trampert, O. Brandt, L. GeelhaarGarrido, Appl. Phys. Lett. 108 202101 *Contact: [email protected]

Molecular beam epitaxy of GaN nanowires on flexible metal foils:

, M. Ramsteiner1,

, S. Fernández-Garrido1

7, 10117 Berlin,

Norwegian University of Science and

approach for the achievement of nearly vertically oriented GaN nanowires on a

stalline metal foil the introduction of a multilayer

the substrate surface. Multilayer graphene is found to efficiently interrupt the epitaxial relation between the growing GaN nanowires and the grains in the foils without the introduction of a detrimental insulating amorphous oxide

. Obtained results represent a first important step towards the fabrication of

nanowire based devices on

Fig. 1: Scanning electron micrographs showing assembled GaN nanowires on a Ti foil

covered by a crystalline (a)–(b) and an

amorphous native oxide (c)–(d) before nanowire

G. Gao, C. Pfüller, A. L. Geelhaar and S. Fernández-

202101 (2016)

berlin.de


B5

Integrated Photoconductive THz Emitters and Detectors made of Fe-doped InGaAs

Steffen Breuer ¹*, Björn Globisch¹, Robert B. Kohlhaas¹, Martin Schell¹,

Mykhaylo P. Semtsiv², W. Ted Masselink²

¹ Fraunhofer Heinrich Hertz Institute for Telecommunications HHI, Einsteinufer 37, 10587 Berlin ² Humboldt University Berlin, Department of Physics, Newtonstrasse 15, 12489 Berlin

In non-destructive testing and industrial process monitoring, reflection geometry is commonly preferred over transmission, because only one-side access to the sample is possible. State-of-the-art terahertz (THz) time domain spectroscopy (TDS) systems hitherto use different emitter and detector devices [2-4], such that either an angled THz beam path or a beam splitter is required to enable reflection measurements. This leads to rather bulky and complex setups. An integrated THz device, combining the emitter and detector on a single chip, would significantly facilitate reflection measurements. Thus, the ideal photoconductive material for competitive integrated devices is compatible to the excitation with 1550 nm femtosecond pulses and can be used as THz emitter and THz receiver (i.e. detector) at the same time.

Here, we show that Fe-doped InGaAs grown at temperatures around 400 °C by gas-source molecular beam epitaxy (GSMBE) combines all these properties [1]. Due to the relatively low growth temperature during Fe doping, concentrations up to 5×1020 cm-3 can be obtained. In addition, the material features an electron lifetime of 300 fs, a resistivity above 2 kΩ cm and an electron mobility higher than 900 cm²/Vs. Thus, InGaAs:Fe combines the sub-picosecond lifetime required for broadband photoconductive receivers with the high resistivity and the high mobility needed for efficient THz emitters.

We fabricated THz emitter and receiver antennas from Fe-doped InGaAs and compared the THz performance to the respective state-of-the-art photoconductors [2-4]. The InGaAs:Fe emitter reaches an output power of 75 µW for a bias voltage of 150 V, which is comparable to the standard device [3]. In Fig. 1 the power spectrum detected by an antenna made of Be-doped

low-temperature-grown InGaAs/InAlAs [4] (blue) is compared with an InGaAs:Fe standard receiver. The measurements were performed with the same photoconductive emitter in a THz-TDS setup based on commercially available components [2]. Both receivers show 6 THz bandwidth with a peak dynamic range above 90 dB. Hence, MBE-grown InGaAs:Fe is a promising material for integrated THz devices, thus allowing lower system prices. [1] B. Globisch, R.J.B. Dietz, R.B. Kohlhaas, T. Göbel, M. Schell, D. Alcer, M. Semtsiv, W.T. Masselink, Iron doped InGaAs: Competitive THz emitters and detectors fabricated from the same photoconductor, J. Appl. Phys., 121, 053102 (2017). [2] N. Vieweg, F. Rettich, A. Deninger, H. Roehle, R. Dietz, T. Göbel, M. Schell, Terahertz-time domain spectrometer with 90 dB peak dynamic range, J. Infrared Millim. Terahz Waves 35, 823 (2014). [3] B. Globisch, R.J.B. Dietz, T. Göbel, M. Schell, W. Bohmeyer, R. Müller, A.Steiger, Absolute terahertz power measurement of a time-domain spectroscopy system, Opt. Lett. 40, 3544 (2015). [4] R.J.B. Dietz, B. Globisch, H. Roehle, D. Stanze, T. Göbel, M. Schell, Influence and adjustment of carrier lifetimes in InGaAs/InAlAs photoconductive pulsed terahertz detectors Opt. Express, 22, 19411 (2014). *Contact: [email protected]

Fig. 1: Power spectrum of an InGaAs:Fe receiver (black) [1] and a standard receiver (blue) [4] detected in a standard THz-TDS system with the same photoconductive emitter.


B6

Epitaxial Growth and Band Structure of Lead Tin Chalcogenide Topological Crystalline Insulators

V. V. Volobuev1,2, P.S. Mandal3, O. Caha4, D. Marchenko3, J. Sanchez-Barriga3,

E. Golias3, A. Varykhalov3, O. Rader3, G. Bauer1 and G. Springholz1 1Institut for Semiconductor and Solid State Physics, JKU, Altenbergerstr. 69, 4040 Linz, Austria

2National Technical University "KhPI", Frunze Str. 21, 61002 Kharkiv, Ukraine 3Helmholtz-Zentrum Berlin, BESSY II, Albert Einstein Str. 15, D-12489 Berlin, Germany

4Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic

Topological crystalline insulators (TCI), where topological surface states (TSS) are protected by crystal symmetry, have been recently theoretically predicted [1] and experimentally realized for (001) cleaved bulk samples of SnTe and solid solutions of Pb1-xSnxTe and Pb1-xSnxSe [2-4]. TSS have been indeed observed by angle resolved photoemission spectroscopy (ARPES). Existence of TSS and studies of topological nature of other surfaces are certainly of interest but the growth of bulk single crystals in other orientations remains challenging [5]. Moreover simultaneous observation of conduction and valence band surface states by ARPES in TCIs based on SnTe is difficult due to highly p-type doping nature of these materials.

In this work, molecular beam epitaxy (MBE) of (111) oriented Pb1-xSnxTe and Pb1-

xSnxSe heteroepitaxial layers grown on BaF2 substrates is demonstrated and their structural and electronic properties investigated. By control of the growth conditions, high quality epilayers with different Sn concentration were obtained. The carrier concentration and thus, the position of the Fermi level is controlled by Bi-doping. Hall effect measurements performed at low temperatures confirmed excellent quality of the samples and mobility of order of 10000 cm2V-1s-1 was achieved that makes further investigations of transport and magneto-optical properties of the samples very perspective.

ARPES studies were performed at the PGM-1 synchortron beameline at BESSY II. Temperature and Sn content dependent E (k//) maps recorded around the -point. For certain temperatures and Sn concentrations, formation of TSS and band gap closing were observed. In addition, a

giant Rashba splitting is observed for Pb1-

xSnxTe samples which can be controlled by Bi doping. The value of Rashba parameter

as large as αR=3.5 eVÅ can be achieved for our samples, which comparable to the values reported for other giant Rashba splitted systems.

[1] T.H. Hsieh, et al., Nature Comm., 3, 982 (2012). [2] S.-Y. Xu, et al., Nature Comm., 3, 1192 (2012). [3] Y. Tanaka, et al., Nature Phys., 8, 800 (2012). [4] P. Dziawa, et al., Nature Mater., 11, 1023 (2012). [5] Y. Tanaka, et al., Phys. Rev. B, 88, 235126 (2013). [6] V. V. Volobuev et al., Advanced Materials, 29, 1604185 (2017). *Contact: [email protected], [email protected]

Fig. 1: (a) XRD pattern, (b) reciprocal space map around the asymmetric (513) reflection, (c) RHEED pattern, (e) AFM image with (d) line profile and (f) ARPES spectrum for (111) Pb1-

xSnxTe epilayer with xSn= 0.46.



C1

GaAs-based core/shell nanowires with extremely large lattice mismatch grown on Si substrates

L. Balaghi1,2, R. Hübner1, G. Bussone3, R. Grifone3, J. Grenzer1, M. Ghorbani

Asl1, A. Krasheninnikov1, G. Hlawacek1, H. Schneider1 , M. Helm1,2 and E. Dimakis1*

1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf,

Dresden, Germany 2 Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, Dresden,

Germany 3 PETRA III, Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany

The geometry and high surface-to-

volume ratio of nanowires offer unique possibilities for strain engineering in epitaxial semiconductor heterostructures with large lattice mismatch. In addition, the possibility to grow nanowires of high crystal quality epitaxially on Si substrates adds to their technological significance. In this work, we have investigated the growth of free-standing GaAs/InxGa1-xAs and GaAs/InxAl1-

xAs core/shell nanowires on Si(111) substrates by molecular beam epitaxy, the accommodation of the lattice mismatch therein, and its effect on the nanowire properties.

Very thin GaAs core nanowires (20-25 nm in diameter) were grown in the self-catalyzed mode with a sufficiently low number density (to avoid beam shadowing effects) on SiOx/Si(111) substrates, after an in situ treatment of the latter with Ga droplets. This resulted in zinc blende nanowires with their axis along the [111] crystallographic direction and six 1-10 sidewalls. Subsequently, conformal overgrowth of the InxGa1-xAs or InxAl1-xAs shell was obtained only under kinetically limited growth conditions that suppressed mismatch-induced bending phenomena.

The strain in the core and the shell was studied systematically as a function of the shell composition and thickness. To that end, we used Raman scattering spectroscopy, transmission electron microscopy and synchrotron X-ray diffraction, and compared the results with theoretical predictions based on continuum elasticity and density functional theories. Our results demonstrate that highly mismatched core/shell nanowires with

defect-free interface can be obtained beyond what is possible in thin film heterostructures.

More interestingly, nanowires with strain-free shell and fully strained core can be grown under certain conditions. The large strain in the GaAs core is expected to have a strong effect on its fundamental properties. Here, we demonstrate a large shrinkage of the band gap, which can be as high as 35 % depending on the composition of the shell.


Fig. 2: Photoluminescence from GaAs/In0.44Al0.56As core/shell nanowires showing the large band gap shrinkage of the tensely strained GaAs core.

Fig. 1: Color coded elemental map showing the radial distribution of In and Ga in GaAs/In0.20Ga0.80As core/shell nanowires as measured by energy-dispersive X-ray spectroscopy.


C2

Self-catalyzed grown InAs/GaSb core-shell nanowire arrays

M.I. Lepsa 1,2*, D. Arumugam 1,2, S. Abusuleiman1,2, T. Rieger 1,2, S. Schmult 3,4,T. Mikolajick 3,4 and D. Grützmacher 1,2

1 Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany2 Jülich Aachen Research Alliance for Fundamentals of Future Information Technology (JARA-FIT), Germany3 TU Dresden, Electrical and Computer Engineering, Institute of Semiconductors and Microsystems, Germany

4 NaMLab gGmbH, Germany

InAs and GaSb are almost lattice matched belonging to the so called ’’6.1Å family’’ [1]. When in contact, the structure has a broken gap heterointerface. In a core-shell nanowire (NW) geometry, these particularities make the combination intere-sting for low power electronic devices (TFETs) and the study of new physical properties, i.e. two-dimensional topological isolator behavior [2]. The selective growth in array offer the advantage of easier growth parameter optimization and better uniformityof the core-shell structure. In this paper, we present the growth and morphological and structural analysis of InAs/GaSb core-shell NW arrays. Preliminary results of DC elec-trical measurements are also discussed.

For the InAs/GaSb core-shell NW array growth, Si (111) substrates covered with 20 nm thermal SiO2 were used. Two-dimensional, periodic arrays of nano-sized holes were patterned in the oxide thin filmusing E-beam lithography and dry and wet chemical etching. The core-shell NWs were grown by MBE using for both As and Sb, valved cracker sources. The growth of InAs NW arrays was optimized regarding the yield and morphology, the best growth parameters being substrate temperature(Ts) 480°C, In rate 0.08 µm/h and As beam equivalent pressure (BEP) 4x10-5 mbar. It came out that the substrate preparation is crucial for achieving a high NW yield. Based on previous results [3], the growth of GaSb shell was investigated similarly obtaining optimum growth conditions for Ts 330°C, Ga rate 0.1 µm/h and SbBEP 1.5x10-6 mbar. Fig. 1 shows an SEM image of an InAs/GaSb core-shell NW array.

Fig.1: SEM image of an InAs/GaSb core-shell NW array.

The coherent epitaxial growth was proved by TEM analysis. The low lattice mismatch (0.6%) between InAs and GaSb combined with the one-dimensional geometry results in misfit dislocation free core–shell NWs.

Additionally, the TEM results show that the crystalline structure of the InAs core NWs, with stacking faults and twins, continues into the GaSb NW shell.

[1] H. Kroemer, Phys. E 20, 196 (2004).[2] L.Du et al., Phys. Rev. Lett. 114, 096802 (2015)[3] T. Rieger et al, Nanoscale 7, 7356 (2015).



C3

Selective Area Epitaxy and Doping of Catalyst-Free GaAs Nanowires on Silicon

D. Ruhstorfer 1*, H. Riedl 1, J. J. Finley 1 and G. Koblmüller 1*

1 Walter Schottky Institut & Physics Dept., TU Munich, 85748 Garching, Germany

III-V semiconductor nanowires (NW) have gained a lot of interest for their ability to be integrated on silicon due to their small footprint and therefore efficient strain relaxation mechanism. With molecular beam epitaxy (MBE), a lot of research has been focusing on catalyzed growth of NWs in the vapor-liquid-solid (VLS) growth mode using either metallic, most prominently gold, or group III element droplets.

For the realization of optoelectronic devices like solar cells, LEDs or electrically pumped lasers using NWs, control of the doping profiles is key and directly affects performance when designing the necessary pn- or pin-junctions. Even though aspect ratios for VLS grown NWs are typically superior to NWs grown using selective area epitaxy (SAE), doping these structures directly proofed difficult due to non-uniform incorporation of dopants during growth [1] and the reservoir effect that is caused by the droplet catalyst [2]. Particularly in GaAs, while n-type doping using the amphoteric dopant silicon is well established for growth directly from the vapor phase in planar samples, only p-type material could be realized so far for VLS NWs. Literature from liquid phase epitaxy (LPE) suggests that the preferential incorporation on Ga lattice sites only occurs for temperatures beyond 860°C [3], which are inaccessible in the usual MBE VLS growth.

To date, most investigations of SAE growth of catalyst-free GaAs NW arrays have focused on the nucleation and growth kinetics during chemical, i.e., MOCVD-based processes. In contrast, growth kinetics studies have not yet been performed for physical, i.e., MBE-based processes, where differences in the surface reactivities, incorporation and adsorption/desorption kinetics are expected.

In this contribution, we present our recent advances in establishing the selective area epitaxy of completely catalyst-free GaAs NWs on silicon (fig. 1). We achieve this by applying a special surface treatment to our SiO2 masked nanoscale apertures before growth, which transforms the usual 7x7 silicon surface to a 1x1-As terminated surface reconstruction. We explore the effects of mask opening diameter, pitch, V/III flux ratio and growth temperature with respect to growth rate and morphology. In addition, we probe the microstructure of our nanowires using TEM.

Furthermore, we show preliminary results of the influence of silicon doping on the growth kinetics and morphology.

[1] J. Dufouleur, et. al., “P-doping mechanisms in catalyst-free gallium arsenide nanowires”, Nano Lett. 10(5), 1734–1740 (2010). [2] K. A. Dick, et. al., “Controlling the abruptness of axial heterojunctions in III–V nanowires: beyond the reservoir effect”, Nano Lett. 12(6), 3200–3206 (2012). [3] P. D. Greene, “Growth of GaAs ingots with high free electron concentrations”, J. Crystal Growth 50, 443 (1980). *Contact: [email protected]

[email protected]

Fig. 1: GaAs nanowires with high aspect ratios grown on silicon without a catalyst.


C4

MBE-grown Ge nanowires: The co-effect of atomic hydrogen and catalyst spreading

T. Pejchal 1*, T. Musálek 2, L. Kachtík 1, T. Šikola 1,2 and M. Kolíbal 1,2

1 CEITEC – Central European Institute of Technology, Brno University of Technology, Purkyňova

123, Brno 612 00, Czech Republic 2 Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology,

Technická 2, Brno 61669, Czech Republic

Molecular Beam Epitaxy is a convenient method for the growth of semiconductor nanowires via VLS (vapour-liquid-solid) process. It allows not only superior control over the deposition parameters (e.g. sample temperature, deposition rates, materials’ purity and UHV conditions), but also to introduce different gases during the deposition. This allows us to disentangle the impact of different processes on the nanowire growth (such as diffusion and surface passivation), in contrast to chemical methods of nanowire growth.

In this poster, we present and compare the VLS growth of germanium nanowires from gold catalyst nanoparticles I) under UHV conditions, II) in the presence of atomic hydrogen. The synergic effect of atomic hydrogen passivation and catalyst spreading is described.

Germanium nanowires grown in UHV adopt <110> growth direction exclusively, irrespective of substrate orientation. On the contrary, when atomic hydrogen is present, the nanowires grow preferentially along <111> direction. Furthermore, the overall morphology is changed (see Fig.1).

The explanation is as follows: With atomic hydrogen passivating the nanowires’ sidewalls, the out-diffusion of Au atoms from the catalyst is suppressed, thus there is no preferred sidewall orientation. Therefore, the catalyst droplet adopts the optimal growth geometry leading to <111> growth direction. However, in ultra-high vacuum, 111 sidewalls are energetically preferred due to Au decoration. Therefore, the catalyst droplet is constrained and the growth proceeds in <110> direction with a different morphology.

Fig. 1: a,b) The Ge nanowires grown in ultra-high vacuum (UHV) adopt <110> growth direction irrespective of substrate orientation. Some of the Au catalyst droplets are lost. c,d) When atomic hydrogen is introduced (2·10-3 Pa), the nanowires grow preferentially along <111> direction and the overall morphology is changed. Published in [1].

[1] M. Kolíbal et al., Nano Letters 16, 4880 (2016). *Contact: [email protected]


C5

The role of MBE epitaxial grown Fe/Pt bilayers in optimizing the spin-pumping induced inverse spin Hall voltage and the THz

emission

S. Keller 1, L. Scheuer 1 G. Torosyan2, T. Kehagias3, B. Hillebrands1, R. Beigang 1,2, E. Th. Papaioannou1, *

1Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität

Kaiserslautern, Erwin-Schrödinger-Str. 56, 67663 Kaiserslautern, Germany 2Photonic Center Kaiserslautern, Kaiserslautern, 67663, Germany

3Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

The generation of a spin current via the spin-pumping effect (SP) and its detection through the inverse spin Hall effect (ISHE) is a key topic of research in the spintronics community [1]. A spin current is generated at the interface between a ferromagnetic material (FM) or a ferrimagnetic insulator (for example, YIG) and a nonmagnetic metal (NM) by a precessing magnetization in the magnetic layer. Recently, the decisive role of the ISHE effect on extending the field of spintronics in the terahertz regime was revealed [2,3].

The efficiency of spin-pumping depends on the transparency of the interface quantified by the parameter termed spin mixing conductance [1]. Here, we structurally modify the interface transparency by using molecular beam epitaxy method (MBE) in Fe/Pt based heterostructures [4,5]. We furthermore introduce a tunnelling MgO barrier at the FM/NM interface in order to probe the ISHE [6].

Fe/Pt and Fe/MgO/Pt samples series were prepared with the MBE method with Fe and Pt thicknesses ranging from 0.5 nm to 12 nm and MgO thicknesses from 0.5 to 2 nm. We show that by optimizing the degree of interfacial epitaxy between Fe and Pt large spin Hall angles can be obtained in Pt together with efficient generation of broadband terahertz radiation.

[1] A. Hoffmann, IEEE Trans. Magn. 49, 5172 (2013) [2] T. Seifert et al., Nat Photon 10, 483–488 (2016). [3] T. Kampfrath et al., Nat. Nano 8, 256–260 (2013). [4] A. Conca et al., Phys. Rev. B 93, 134405 (2016). [5] E. T. Papaioannou et al., Appl. Phys. Lett. 103, 162401 (2013). [6] L. Mihalceanu et al. Appl. Phys. Lett. 110, 252406 (2017) *Contact: [email protected]

Fig. 1: High resolution transmission electron microscopy image from an epitaxial grown Fe/Pt bilayer. The 111 MgO, 011Fe, and 111Pt lattice fringes are clearly resolved, along the [011]MgO-Pt//[001] Fe projection direction [4].


Membranbälge und Vakuumkomponente

Straubstrasse 11 CH – 7323 Wangs www.mewasa.ch / [email protected]


C6

Magnetic Properties of Ferromagnet/Semiconductor/Ferromagnet Hybrid Trilayers Grown using Solid-phase Epitaxy

S. Gaucher*, B. Jenichen, U. Jahn, A. Trampert, and J. Herfort

Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany

The combination of ferromagnetic Heusler alloys (FM) with semiconductors (SC) is of great interest for a variety of applications in the field of spintronics. However, the development of new devices is limited by the difficulty of growing epitaxial SC over metals due to large differences in crystallization energies, which cause undesirable interfacial reactions (usually metals are grown over SC substrates). This aspect is problematic because spin-injection requires sharp interfaces with well-defined tunnel barrier.

We developed a solid-phase epitaxy approach and explored its possibilities to create lattice-matched FM/SC/FM thin film stacks while preventing interfacial reactions [1]. Instead of direct MBE growth, a thin amorphous layer of Ge is deposited on Fe3Si and then crystallized slowly by annealing. Capping FM layers such as Fe3Si or Co2FeSi could then be grown on top of this newly crystalline Ge by standard

low-temperature MBE. In this process, a superlattice develops in the Ge film, as seen in Fig. 1, most probably caused by a diffusion of Fe and Si. Nonetheless, XRD, TEM, RHEED and EBSD indicate that the

films are in most cases lattice-matched single crystals with impeccable interfaces.

The magnetic properties of the trilayers were then studied with a SQUID magnetometer. The two FM layers, made of different materials and/or having different

thicknesses, are expected to have different coercive fields. Indeed, as seen in Fig. 2, a switching of the thicker Fe3Si layer occurs first within 5 Oe. The thinner Co2FeSi film then follows at a slightly higher field. The possibility to control individually the magnetization of the films (parallel or anti-parallel) is an important step to realize spintronic devices based on the tunnel magnetoresistance effect.

[1] S. Gaucher et al., Appl. Phys. Lett. 101, 102103 (2017).


Fig. 1: HR TEM of a Fe3Si/Ge/Fe3Si sample with thicknesses of 36/4/12 nm showing fully crystalline layers and Ge(Fe,Si) superlattice. (from [1]).

Fig. 2: Magnetization of a Fe3Si/Ge/Co2FeSi sample with thicknesses of 36/6/12 nm along the [110] direction. As the external magneticfield is swept, the two FM layers switch their orientation independently due to having different coercivities.


D1

New Optical selection rules from GaAs quantum dots via

highly variable uniaxial stress actuators X. Y. Yuan1,2*, F. Weyhausen-Brinkmann3, J. Martín-Sánchez1, V. Křápek4, H. H. Huang1, Y. H. Huo1,2,5,6, G. Piredda7, R. Trotta1, S. Stroj7, J. Edlinger7,

G. Bester3, O. G. Schmidt2, A. Rastelli1*

1 Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstraße 69, 4040, Linz, Austria 2 Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany 3 Institut für Physikalische Chemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany 4 Central European Institute of Technology, Brno University of Technology, Purkynova 123, 61200 Brno, Czech Republic 5 Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, 230026, Hefei, China 6 CAS-Alibaba Quantum Computing Laboratory, USTC Shanghai, 201315, Shanghai, China 7 Forschungszentrum Mikrotechnik, FH Vorarlberg, Hochschulstr. 1, 6850 Dornbirn, Austria A novel micro-machined piezoelectric actuators featuring geometrical strain amplification is developed to explore the optical properties of GaAs quantum dots subject to variable uniaxial tension up to mechanical fracture. First of all, due to the modification of band gap from the stress, the emission energy of an exciton confined in a GaAs "artificial atom" can be continuously shifted by more than 100 meV, as illustrated by scanning it through the D2 and D1 transitions of 87Rb vapors. This strain-induced shift overcompensates the confinement energies, leading to emission well below the bandgap of GaAs, and this is the largest reported so far for piezoelectric-semiconductor devices. Second, valence band mixing leads to dramatic changes in the optical selection rules for excitonic transitions: one light component emitted from the sample

surface becomes fully polarized perpendicular to the pulling direction while initially forbidden vertically polarized transitions become bright. By exploiting hole mixing and a wedge-waveguide geometry we are able to observe the whole transition process of neutral exciton under variable uniaxial stress without resorting to the magnetic field. Under the high tension stress effect, two new bright states displace the old ones, which indicates a new quantization axis should be chosen. These results show a promising route to tailor the polarization properties of single-photons emitted by epitaxial quantum dots and allow us to test the reliability of state-of-the-art methods (k·p and empiricial pseudopotential) under extreme conditions. *Contact: [email protected] or

[email protected]


D2

Novel quantum optical devices based on droplet epitaxial GaAs/AlGaAs quantum dots

Huiying Huang 1*, Saimon Filipe Covre da Silva1, Xueyong Yuan1 and Armando

Rastelli1

1 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Altenbergerstr. 69, A4040, Linz, Austria

Epitaxial growth Semiconductor quantum dots (QDs) are currently popular as promising sources of single and entangled photon pairs in the future application in linear-optical quantum computation and quantum communication. Compared with the commonly studied InGaAs QDs, GaAs QDs have many advantages such as no built-in strain, controllable shape, flexible choice of composition, Fourier-limited emission, nuclear spin of Ga isotopes smaller than In, which make GaAs QD a good choice for quantum-dot entanglement sources in future quantum technologies. [1, 3] However, the absence of strain disables the common strain-driven growth method used for InGaAs QDs. Many new approaches have been developed to overcome this problem. For example, Al-droplet-epitaxy growth method is used here to obtain high quality GaAs/AlGaAs QDs. [2] Another appealing feature of epitaxial QDs is that they can be embedded in various optical and electronic structures like optical cavity and p-i-n doped diode. [3] Combined with the post-grow processing, such as changing surface topography, intergrating the expilayer with other materials , very complex devices can be obtained. As one of the pioneer paper [4] has pointed out, an idea entangle-photon-pair source need to meet four demands: (i) deterministic generation, (ii) high fidelity, (iii) Indistinguishability, and (iv) high collection efficiency. On one of the recent paper, GaAs QD system has already been proved as comparable or even better system than InAs for emitting (ii) high fidelity and (iii) high indistinguishability entangled photon pairs. [1] Profit from the excellent nature of making complex and compact device, GaAs QD system may also achieve the goals of (i) deterministic generation and (iv) high collection efficiency in the very near future.

In this work, I will introduce several devices based on GaAs/AlGaAs QDs aimed at achieving bright emission and electrical control. [5]

Reference [1] Huber D., et al., Nature Communications 8,

15506 (2017) [2] Huo Y., et al., Appl. Phys. Lett. 102 (15),

152105(2013) [3] Rastelli A, et al. Phys. Rev. Lett. 92 166104 [4] Lu C. et al. Nature Photonics 8, 174–176 (2014) [5] Huang H., et al., ACS Photonics 4 , 868-872

(2017).



D3

Fig. 1: a Exciton emission wavelength distribution for two different samples tailored for coupling to the D1 and D2 atomic transitions of Rubidium. b Real and imaginary part of the two-photon density matrix c Entanglement fidelity of GaAs/AlGaAs QDs as a function of fine structure splitting S

Solid-state ensemble of highly entangled photon sources at rubidium atomic transitions

R. Keil1*, M. Zopf1, Y. Chen1, B. Höfer1, J. Zhang1, F. Ding1,2 and O. G. Schmidt1,3

1Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden, Germany 2Institut für Festkörperphysik, Leibniz Universität Hannover, 30167 Hannover, Germany 3Material Systems for Nanoelectronics, TU Chemnitz, 09107 Chemnitz, Germany

Polarization-entangled photon pairs play

a key role in scalable quantum communication applications. They enable secure quantum key distribution [1], robust qubit transfer via teleportation [2] and can be used to distribute entanglement between separated computation nodes, rendering even a “quantum internet” possible [3].

However, deterministic sources of highly entangled photon pairs challenge the community for already more than two decades. Semiconductor quantum dots are among the leading candidates for this task, offering pure single photon pair emission with high internal quantum efficiency, outperforming probabilistic sources based on spontaneous parametric down-conversion.

Despite various investigated structures and material systems [4,5,6,7], most quantum dot species still suffer from drawbacks such as extremely low yield, low degree of entanglement and poor wavelength control, blocking the way for scalable applications.

Here, we show that with an emerging family of GaAs/AlGaAs quantum dots grown by droplet etching and nanohole infilling, it is possible to obtain a large solid-state emitter ensemble of highly entangled photons pairs on a wafer - without any post-growth tuning [8]. Under pulsed resonant two-photon excitation, all measured quantum dots emit single pairs of entangled photons with ultra-high purity, high degree of entanglement and ultra-narrow wavelength distribution at rubidium transitions. Therefore, this material system is an attractive candidate for the realization of a solid-state quantum repeater - among many other key enabling quantum photonic elements.

[1] A. K. Ekert, Phys. Rev. Lett. 67, 661 (1991) [2] C.H. Bennett et al., Phys. Rev. Lett. 70, 1895 (1993) [3] H. J. Kimble, Nature 453, 1023-1030 (2008) [4] G. Juska et al., Nat. Photonics 7, 527 (2013) [5] M. Müller et al., Nat. Photonics 8, 224-228 (2014) [6] M. A. Versteegh et al., Nat. Commun. 5, 6298 (2014) [7] T. Kuroda et al., Phys. Rev. B 88, 031306 (2013) [8] R. Keil et al., Nat. Commun. 8, 15501 (2017)


D4

Phase separation in metastable Ge1-xSnx epilayers induced by free running Sn precipitates

H. Groiss1,2,3, M. Glaser1, M. Schatzl1, M. Brehm1, D. Gerthsen3 and F. Schäffler1

1 Semiconductor Division, Johannes Kepler University Linz, Austria

2 Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Austria 3 Laboratory for Electron Microscopy, Karlsruhe Institute of Technology, Germany

Recently, optical gain was demonstrated

in Ge1-xSnx alloys [1], which are the only known group-IV materials that assume a direct band gap for compositions x > 10%. However, Ge and Sn are immiscible over >98% of the composition range, which renders direct-gap Ge1-xSnx epilayers inherently metastable.

Here, we address the temperature stability of pseudomorphic Ge0.9Sn0.1 films grown by MBE on Ge(001) substrates [2]. In particular, we studied by in-vivo scanning electron microscopy (SEM) the influence of post-growth annealing steps. Decomposi-tion of the metastable epilayers was found to set in above 230°C, the melting point of Sn.

Video sequences taken during the annealing experiments reveal the crucial role of liquid Sn precipitates in the phase separation process (Fig. 1). Driven by a gradient of the chemical potential, the Sn droplets move on the surface along <110> or <100> directions, thereby taking up Sn and Ge from the intact Ge1-xSnx layer. Whereas Sn-uptake increases the volume of the melt, dissolved Ge becomes re-deposited as a single-crystalline Ge trail by liquid-phase epitaxy (LPE). Secondary droplets launched from the Ge trails into adjacent GeSn regions lead to an avalanche-like transformation front between the GeSn film and re-deposited Ge (Fig. 1(c)).

This peculiar decomposition process was confirmed by cross sectional TEM and EDX analyses along the trajectories of Sn droplets. In front of the moving Sn droplet the GeSn film remains in the as-deposited strain and composition state, whereas the trail consists of almost pure, single crystalline Ge which exposes low energy surface facets (Fig. 1(b)). The Sn droplets extend all the way down to the Ge substrate

and were found to take up a supersaturated Ge concentration of about 10%.

Overall, each of the free-running Sn droplets behaves like a microscopic LPE reactor: The strained and metastable GeSn film on the one side acts as a feeding medium, whereas the opposite side leads to epitaxial deposition of the Ge trail. This process propels the droplets making phase separation in these metastable GeSn alloys particularly efficient already at rather low temperatures.

Fig. 1: SEM images taken from real-time video sequences of the precipitate-induced phase separation process in GeSn epifilms. The Sn droplets in (a) and (b) appear bright, the corrugate trails consist of single-crystalline Ge. (a) and (b) were recorded in-vivo at 250°C, (c) at 350°C.

[1] S. Wirths et al., Nature Photonics 9, 88 (2015) [2] H. Groiss et al., arXiv 1705.05156 correspondence to: [email protected]


D5

Initial growth of tin on silicon and germanium surfaces

N. Braud, Th. Schmidt, and J. Falta*

Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28357 Bremen, Germany

The integration of Sn into Si and SiGetechnology offers a great potential for futureapplications. With increasing Sn content inGeSn alloys, the carrier mobility isenhanced [1]. Moreover, Sn may offer aprecise control of the electronic bandstructure for Si photonics [2], and GeSnfilms are very promising as stressors for thefabrication of tensile strained Ge layers.

We have investigated the adsorption andinitial growth of Sn on Si(001), on Ge(001),and on compressively strained pseudo-morphic Ge layers grown on Si(001). Theevolution of surface reconstruction andmorphology during Sn deposition wasmonitored in situ with low-energy electrondiffraction (LEED) and microscopy (LEEM).Room-temperature (RT) Sn deposition,followed by annealing between 570°C and680°C, is compared to Sn growth atelevated temperatures.

On Si(001) substrates, RT deposition ofSn leads to different surface reconstructionsafter annealing. Depending on Sn coverage,c(4×4), (1×n), (2×n), c(8×4), and finally a(5×1) reconstructions were observed in therange of up to 1.5 monolayers (ML) Sn.Many of these reconstructions undergo areversible phase transition at about 535°C,either into a (2×1) or into a (1×1) structure.The surface phase diagram is depicted inFig. 1. It is in good agreement with earlierwork by Ueda et al. [3]. Unlike theseauthors, however, we do not observe a(2×6) reconstruction near 0.4 ML. Instead,we found a varying n in the range from 4 to5. The situation is different, when Sn isgrown on Si(001) at elevated temperatures.In the investigated range from 470°C to580°C, (1×n) and (2×n) periodicities withvery large n evolve immediately after thestart of the deposition. With increasingcoverage, n is reduced continuously downto n=5. This points to a missing-rowarrangement of Sn-Si and, progressively,Sn-Sn dimers. Upon further Sn growth, allLEED superstructure spots vanish and,finally, the high-coverage (5×1) phase

evolves. For Sn deposits in excess of 1.5ML, the growth of pyramidal islands isobserved with LEEM. A three-dimensionalreciprocal-space analysis with LEEDreveals the 113 orientation of the sidefacets of these Stranski-Krastanov islands,in agreement with earlier STM work [4].

On strained pseudomorphic Ge films onSi(001), the structural evolution upon Sndeposition is very similar. The only notabledifference is that at low coverage a (2×n)periodicity prevails from the beginning,which originates from the Ge wetting layer[5].

For Sn on bulk Ge(001) substrates, thedevelopment of the surface reconstruction isalso similar to that on Si(001). However,though we observe a (1×n) periodicity, ourdata does not provide clear evidence forother reconstructions, such as c(8×4).Nevertheless, n shows the same trend withcoverage as for Sn/Si(001): it starts at verylarge values and is reduced continuously ton=6.4. Compared to the larger-lattice-mismatch systems Sn/Si(001) andSn/Ge/Si(001), where finally n=5 is reached,this finding points to strain as driving forcefor these reconstructions.

[1] K.L. Low et al., J. Appl. Phys. 112, 103715 (2016).[2] S. Wirths et al., Nature Photonics 9, 88 (2015).[3] K. Ueda et al., Surf. Sci. 145, 261 (1984).[4] A.A. Baski et al., Phys. Rev. B 44, 11167 (1991).[5] T.U. Schülli, Semic. Sci. Techn. 26, 064003 (2011).

*Contact: falta @ ifp.uni-bremen.de

Fig. 1: Phase diagram for Sn/Si(001).


D6

Carbon-mediated epitaxy of SiGe virtual substrates on Si(001)

J.Schmidt 1*, D.Tetzlaff 1, and H.J. Osten 1,2

1 Institute of Electronic Materials and Devices, Leibniz Universität Hannover, Schneiderberg 32, 30167 Hannover, Germany

2 Laboratory of Nano and Quantum Engineering, Leibniz Universität Hannover, Schneiderberg 39, 30167 Hannover, Germany

We report on the effect of carbon

submonolayer deposition on the growth of thin Si1-xGex (SiGe) layers on Si(001) substrates for ultra-thin virtual substrate (VS) applications.

SiGe VS are of interest for various applications in semiconductor technology. However, conventional methods like graded buffer layers [1] have limitations regarding layer thickness. Alternative methods, as low temperature growth [2] or the use of surfactants [3], can greatly reduce the VS layer thickness but come with other difficulties concerning defect densities. It was shown for Ge epitaxy on Si(001) that the low-temperature deposition of Ge in combination with a submonolayer of Carbon and subsequent annealing can successfully suppress island formation and lead to a smooth, relaxed layer at arbitrary thick-nesses.[4] We adapted this process flow to evaluate the usability for SiGe layer growth. The process we used consists of several growth steps: During an initial deposition step at a low temperature, a thin SiGe layer is deposited onto the substrate. This is followed by deposition of a sub-monolayer of C and subsequent annealing to enable further crystallization and relaxation of the SiGe layer. A subsequent SiGe growth step at elevated temperature yields a carbon-free surface and the desired layer thickness.

We investigated several growth para-meters, such as the initial growth tempera-ture, the Ge fraction of the layer, the annealing ramp and the carbon amount. The growth took place in a DCA S1000 MBE cluster system. Si and Ge were evaporated from electron gun evaporators, a sublimation cell was used for C depo-sition. The growth was in situ monitored with RHEED and ex situ characterized with XRD, XRR, SEM and TEM.

From in situ RHEED measurements during all stages of the growth process, we

observe that the layer shows crystalline and amorphous parts throughout the first SiGe deposition step. The streaky RHEED pattern during annealing and throughout the second growth step indicates a smooth layer. Transmission electron microscopy investi-gations in cross-section confirm the layer thickness of 30 - 70 nm and the low surface roughness of the layers. The defect structure analysis is subject of ongoing investigations.

The SiGe layers show a Ge fraction between 0.44 - 0.81, which was obtained from reciprocal space maps around the 113+ reflection, as can be seen in Fig. 1.

Fig. 1: reciprocal space map around the 113+ reflection for a CME-SiGe sample with a layer thickness of 70 nm.

The samples with Ge fractions at x = 0.75 – 0.80 are almost fully relaxed (R = 93%), whereas the the layers with x = 0.44 – 0.5 show a degree of relaxation around R =75%

In summary, we propose that carbon-mediated epitaxy is a promising candidate for the growth of ultra-thin, smooth SiGe layers with high degrees of relaxation.

References [1] Fitzgerald et al., Appl. Phys. Lett. 59, 811 (1991). [2] Bauer et al., Thin Solid Films, 369, 152 (2000). [3] Wietler et al., Thin Solid Films, 557, 27 (2014). [4] Tetzlaff et al., Appl. Phys. Lett. 100, 12108 (1991). *Contact: [email protected]



Poster Presentations

Abstracts


P1

Growth of Si, Ge, and SiGe Nanowires

F. Lange*, R. Bansen, Th. Teubner, and T. Boeck

Leibniz Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin, Germany

Nanowires (NWs) are one-dimensional

crystalline objects with specific physical properties due to their reduced dimensionality. The integration of Si and particularly Ge NWs in sophisticated Si electronics would be desirable, but the realization will remain on the level of research and development for years to successfully implement in the industry, as the growth and handling of NWs is a challenging task.

We focus on the controlled growth of Si, Ge, and SiGe NWs on (111)Si substrates by MBE. Hereby, solid sources of the elements, Au, Si and Ge were used. Au serves as catalyst, where the NW growth is located and take place via the VLS mechanism. Our work is targeted on arrays of doped SiGe NWs for thermoelectric devices applicable to high temperatures. NWs could be helpful to improve the figure of merit of such devices by reducing the thermal conductivity due to phonon scattering on the sidewalls and at composition changes inside the NWs.

The precise placement of gold droplets as starting points of NW growth is carried out by coordination of the Au evaporation rate and of the substrate temperature.

The distribution and movement of gold on Si and Ge surfaces varies. When cooling down the substrate, we observe small Au particles on the Si surface, beside the Au droplets. On Ge surfaces these particles are missing. We explain this behavior by a stronger Au wetting behavior, and by inhibited movement of Au atoms on Si surfaces. Moreover, residual silicon suboxide, which is more stable than germanium suboxide, serves as pinning points for Au.

The growth direction of Si and Ge NWs differs, too. Si NWs grow preferably into [111] direction forming alternating (111) and (113) micro-facets at the NWs’ side walls,

whereas Ge NWs grow into [110] direction with microscopically flat (111) side facets [1].

During growth, material is supplied to the Si NWs by diffusion from surface areas between the NWs and from the NWs’ sidewalls. With increasing length of the NWs this process tends to be ineffective, leading to the accumulation of Si or Ge on the substrate surface outside the NWs. To protect the substrate surface from epitaxial growth during NW formation, a temporary in situ oxidation of the surface is applied.

This attempt was preceded by oxidation experiments of the as-prepared Si substrate. RHEED investigation showed that under prevailing MBE conditions a stable Si oxide is only formed when oxygen and silicon are co-deposited.

[1] J. Schmidtbauer, R. Bansen, R. Heimburger, Th. Teubner, T. Boeck; J. Cryst. Growth, 406, 36 (2014) *Contact: [email protected]

Fig. 1: RHEED images show the surface structure of a (111)Si substrate when exposed to oxygen only (left), and when silicon and oxygen are deposited simultaneously (right). The duration of both experiments was 30 min.


P2

Manipulating the Wavefunction of High-Quality 2DEGs in GaAs/AlGaAs using Advanced Gating Techniques

C. Reichl1*, M. Berl 1, J. Scharnetzky1, W. Dietsche1, K. Ensslin1 and W. Wegscheider 1

1 Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland

Our technique of fabricating high-quality 2DEGs in GaAs/AlGaAs above patterned back gates (detailed in abstract “Patterned Back Gates for Ultra-High Quality GaAs/AlGaAs Heterostructure Epitaxy”) allows for a wide range of approaches to probe the physical properties of 2DEGs.

For instance, we are able to tune the

electron density n while keeping the electronic wave function centered in the quantum well. Likewise, the wave function can be shifted towards each of the quantum well’s interfaces with constant n. This allows to study for example the fragile fractional Quantum Hall state at n = 5/2 with respect to electron-electron screening and interface roughness (IR) scattering individually. This provides a significant advantage over earlier investigations, where n and IR scattering could not be varied separately.

In a preliminary study we tuned n from 0.9 to 4.8·1011 cm-2 with a centered wave

function. Characterizing electron mobilities, we measured up to 39.8·106 cm2/Vs, which is the highest value reported so far. Also, we demonstrate a significant dependency of μ on gate configuration (with constant n), reflecting the impact of increased interface roughness scattering (see Fig. 1).

In an effort to utilize the patterned

backgate technique for nanoscale applications, we reduced the distance between patterned back gate and 2DEG to about 100nm while maintaining a high quality of the 2DEG. Usually, the spacing between 2DEG and the impurity-rich surface of the growth substrates is larger by an order of magnitude to minimize the impact of the impurities on the 2DEG quality. Nevertheless, by applying elaborated cleaning procedures we managed to obtain electron mobilities of 5·106 cm2/Vs in such a structure. Based on these results, we will be capable to fabricate nanoscale constrictions, e.g for quantum point contacts, by use of patterned back gates.

Additionally, we investigated a single-

sided doped heterostructure with a wide quantum well (200 nm width) with both top and back gate. It was possible to induce a second 2DEG by accumulation of electrons using the back gate. This way, a 2DEG is created without having a layer of ionized dopants in close vicinity. The density of the lower 2DEG could be tuned between 1 to 4 1010 cm-2. Using the top gate the density in the upper 2DEG can be tuned separately. When controlling the tunneling coupling of the two 2DEGs this would provide a playground to examine exotic quantum liquid states. *contact: [email protected]

Fig. 1: Mapping of top- and back gate voltage with resulting electron mobility (colour coded). The dotted lines represent gate configurations with constant electron density.


P3

Patterned Back Gates suitable for Ultra-High Quality GaAs/AlGaAs Heterostructure Epitaxy

J. Scharnetzky 1*, M. Berl 1, C. Reichl 1, W. Dietsche 1 and W. Wegscheider 1

1 Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland

Gate patterning is mandatory for meso- and nanoscopic scale devices such as quantum point contacts. While patterned top gates can be realized with relative ease, the implementation of patterned back gates is very demanding. Ideally, the patterned back gate needs to be buried between substrate and heterostructure to attain sufficiently low distance between back gate and 2DEG. Moreover, the quality of the heterostructure epitaxy should not be limited by a patterned substrate. We developed a reliable technique to implement patterned back gates for ultra-high quality 2DEGs suitable for nanoscopic devices.

We found a way [1] to overcome the

limitation of prior approaches and define back gate patterns directly on the epitaxial surface of the GaAs substrate using oxygen implantation on silicon doped GaAs substrates to electrically insulate regions (passively written gates). Recently we realized actively written gates by implanting silicon directly on GaAs substrates and subsequent annealing for dopants activation.

The sample fabrication (see Fig. 1) is

efficient, reliable and scalable. It starts with standard photolithography on a GaAs wafer

using photo resist as a selective absorber for the silicon ion implantation, followed by an “epiready” cleaning process as well as dopants activation in a MOCVD system (optional step depending on the growth temperature in the MBE). The samples then are overgrown with the desired heterostructure. Subsequently, mesa-structures with inherently separated contacts for 2DEG and back gate can be defined. The implantation parameters were optimized to achieve reliable gating as well as a minimal impact of the implantation to the surface quality of the substrate.

Our new patterned back gate technology

is especially promising in the following fields (for details on current measurements we refer to abstract “Manipulating the Wavefunction of High-Quality 2DEGs in GaAs/AlGaAs using Advanced Gating Techniques”):

1) Reliable contacting of 2DES and back

gate with a wide gate tuning range without risking electrical shorts.

2) Nanoscopic gating via closely spaced 2DES and back gate (~100nm) while retaining high quality heterostructures

3) Extremely high quality 2DEG accessible by pushing the density limits with patterned top and back gates, reaching world record mobilities

4) Sophisticated gating of double layer 2DEG and/or 2DHG systems which must be tuned independently through a top and a back gate.

[1] M.Berl, L.Tiemann, W. Dietsche, H. Karl, and W. Wegscheider, Appl. Phys. Lett. 108, 132102 (2016)


Fig. 1: The five steps to fabricate heterostructures with patterned back gates. Details are given in the text.


P4

Preparation of bimetallic catalysts for nanowire growth

T. Musálek 1*, T. Pejchal 2, M. Kolíbal 1,2 and T. Šikola 1,2

1 Institution of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2, Brno 616 69, Czech Republic)

2 CEITEC – Central European Institute of Technology, Brno University of Technology, Purkyňova 123, Brno 612 00, Czech Republic

One-dimensional growth is usually, yet not always, performed using metal seed, which

acts as a catalyst for growth itself. It has been shown, that incorporation of impurities from catalyst particle during the growth of nanowires from vapour phase changes their basic properties.

The most frequently used catalyst particle is made from gold. However, gold is responsible for so-called reservoir effect and is known to create deep traps in the band gap decreasing the carrier mobility which renders the nanowires incompatible with the CMOS technology.

In view of this, usage of other suitable materials, or their combinations as catalysts, can suppress unwanted effects or introduce advanced properties which open progressive possibilities for further applications. For example aluminium catalyst particle can lead to massive p-type doping [1], while alloyed gold-gallium catalysts are demonstrated to weaken reservoir effect, which can be used to grow sharp Si/Ge interfaces within the nanowire [2].

In our contribution we will describe preparation process for bimetallic particles with emphasis on gold or silver particle combined with other group III or group V element. Further on, we will demonstrate the results with germanium nanowires grown from these catalysts and discuss their effect on resulting properties.

[1] Moutanabbir, Oussama, et al. Nature 496.7443 (2013): 78-82. [2] Gamalski, Andrew D., et al. ACS nano 7.9 (2013): 7689-7697. *Contact: [email protected]


P5

Site-controlled Ga droplet epitaxy by deposition through shadow masks

V. Zolatanosha and D. Reuter*

Department of Physics, University of Paderborn, Warburger Str. 100, 33098 Paderborn, Germany

Semiconductor quantum dots (QDs) have been an area of intensive research in the past [1, 2, 3, 4].Very high quality QDs can be produced by self-assembly either by the Stranski-Krastanov (S-K) growth mode or via droplet epitaxy [5, 6]. One big disadvantage of self-assembled growth is the random nucleation of QDs on the surface. There are a few approaches which allow controlling the exact position of a single QD for strain-mediated S-K grown InAs QDs quite well [3, 7]. In contrast, for droplet epitaxy, just two groups have reported some degree of site control [8, 9].

In this contribution, we propose selective

area epitaxy (SAE) by employing a movable shadow mask to achieve site-controlled QDs via droplet epitaxy. In SAE the material is deposited locally through apertures in the mask. In our approach, from these local deposits, droplets are formed via self-assembly, ideally one droplet per aperture. Our removable robust shadow mask is based on a nano-patterned 100 nm Si3N4-membrane on a 1 mm thick Si(100) support wafer. The circular apertures have diameters from 5 µm down to 100 nm. The smallest openings are intended for single droplet formation. A crystallization step under As flux would transform the site-controlled droplets into QDs. A GaAs layer, which is deposited on the mask, results in a fresh mask surface, allows for an in-situ hole size reduction and can be re-evaporated without damaging the mask, i.e. the mask can be used many times.

Deposition experiments of Ga through the mask show that one has to minimize the gap between substrate and mask as well as that the diffusion has to be suppressed to obtain a localized deposition governed by the hole size. Therefore, we employ close contact between mask and substrate and deposit the Ga at 100° C substrate temperature. After removing the mask, we

employ an annealing step to form the droplets.

Fig. 1: SEM image of an array of single Ga droplets. By optimizing the Ga amount deposited and the in-situ annealing parameters we were able to induce a single Ga droplet for each aperture with high probability (see Fig. 1). Subsequent crystallization under As flux results in an array of GaAs QDs. [1] D. Bimberg, M. Grundmann, N. N. Ledentsov, Quantum Dot Heterostructures, John Wiley and Sons (1999) [2] P. Michler (Ed.), Single Quantum Dots, Springer (2003) [3] O. G. Schmidt (Ed.), Lateral Alignment of Epitaxial Quantum Dots, Springer (2007) [4] Z. M. Wang (Ed.), Self-Assembled Quantum dots, Springer (2008) [5] J. Wu, Z. M. Wang, J. Phys. D, 47, 173001 (2014) [6] S. Bietti, J. Bocquel, S. Adorno, T. Mano, J. G. Keizer, P. M. Koenraad, S. Sanguinetti, Phys. Rev. B, 92, 075425 (2015) [7] H. B. Lan, Y. C. Ding, Nano Today 7, 94 (2012) [8] J. S. Kim, S. M. Kawabe, N. Koguchi, Appl. Phys. Lett., 88, 072107 (2006) [9] E. M. Sala, M.Bollani, S. Bietti, A. Fedorov, L. Esposito, S. Sanguinetti, J. Vac. Sci. Technol. B, 32,061206 (2014) *Contact: [email protected]

800 nm


P6

Growth and characterization of unstrained GaAs/AlGaAs quantum dots

S.F.C. da Silva 1*, Huiying Huang 1, Xueyong Yuan1 and A.Rastelli1

1 Institute of Semiconductor and Solid State Physics,Johannes Kepler University,Altenbergerstr.

69,A4040, Linz, Austria

Epitaxial semiconductor quantum dots are attracting much interest for their potential use in emerging quantum technologies. These fascinating structures can be created by different approaches, such as the Stranski-Krastanow growth mode, the overgrowth of patterned pits1 or self-assembled nanoholes2 with an optically active AlGaAs/GaAs heterostructure. In turn, nanoholes can be obtained by using Al droplets to locally etch AlGaAs3. This has the versatility of being fully performed in a III-V molecular beam epitaxy system and does not require any kind of ex-situ process. These dots can grow with a highly symmetric shape, resulting exciton emission with a small fine structure splitting4 that could be applied for entangled photon generation5. However some unknown slow relaxation mechanism5resulting in a time-jitter in the photon emission for these dots when exctied non-resonantly. We present here results on the growth of GaAs/AlGaAs dots and the correlation between decay dynamics and dot size. The latter is controlled systematically by changing the amount of GaAs used to fill the AlGaAs nanoholes. (1) Hartmann, A.; Ducommun, Y.; Loubies,

L.; Leifer, K.; Kapon, E. Structure and Photoluminescence of Single AlGaAs/GaAs Quantum Dots Grown in Inverted Tetrahedral Pyramids. Appl. Phys. Lett. 1998, 73, 2322–2324.

(2) Rastelli, A.; Stufler, S.; Schliwa, A.; Songmuang, R.; Manzano, C.; Costantini, G.; Kern, K.; Zrenner, A.; Bimberg, D.; Schmidt, O. G. Hierarchical Self-Assembly of GaAs/AlGaAs Quantum Dots. Phys. Rev. Lett. 2004, 92, 166104.

(3) Heyn, C.; Schnüll, S.; Hansen, W. Scaling of the Structural Characteristics of Nanoholes Created by Local Droplet Etching. J. Appl. Phys. 2014, 115, 24309.

(4) Huo, Y. H.; Rastelli, A.; Schmidt, O. G. Ultra-Small Excitonic Fine Structure Splitting in Highly Symmetric Quantum Dots on GaAs (001) Substrate. Appl. Phys. Lett. 2013, 102, 152105.

(5) Jahn, J.-P.; Munsch, M.; Béguin, L.; Kuhlmann, A. V.; Renggli, M.; Huo, Y.; Ding, F.; Trotta, R.; Reindl, M.; Schmidt, O. G.; et al. An Artificial Rb Atom in a Semiconductor with Lifetime-Limited Linewidth. Phys. Rev. B 2015, 92, 245439.

Contact: [email protected]


P7

Growth control with RAS of highly ordered Ga(As)Sb quantum dots grown on pre-structured GaAs

J. Straßner1*, T.H. Löber2, S. Wolff2, and H. Fouckhardt1

1 Research Group Integrated Optoelectronics and Microoptics, Physics Department,

University of Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern, Germany 2 Nano Structuring Center and State Research Center OPTIMAS, Physics Department,

University of Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern, Germany

Ga(As)Sb quantum dots (QD) are usually grown by self-organization in the Stranski-Krastanov growth mode on a plane GaAs surface. In different publications we have shown that we are able to change the diameter, the height, and the density of the QD as well as their emission wavelength (from 876 nm up to 1309 nm) by variation of the growth parameters [1-3].

Here we report on the opportunity to achieve highly ordered QD on a pre-struc-tured GaAs substrate. An array of holes/de-pressions is milled into the GaAs substrate/ buffer with a gallium focused ion beam (FIB) machine. It is possible to control the density, the depth, and the diameter of the holes. By overgrowth of these structures for optimum growth parameters the QD can be forced to form exactly at the positions of the holes.

During FIB milling surface contamina-tions can occur. Also the samples have a vacuum brake during the transfer from the FIB to the MBE and a native oxide layer is formed on the sample surface. An over-growth of the pre-structured substrate/buffer can only be successful, if these contamina-tions are removed.

Several approaches have been pursued with dry and wet etching outside the MBE chamber. Different heat ramps in the MBE chamber and overgrowth parameters have also been tested. The best results are achieved with a hydrochloric acid etching step before the sample is overgrown with a 50 nm thick GaAs layer.

To control and verify the crystalline struc-ture of the structured surface reflection an-isotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) are used in-situ during the epitaxial process. The recorded RAS spectra are compared with those of unstructured samples.

The QD will grow in the holes, if the

diameter of the dots fits almost the diameter of the holes. The distance from hole to hole is 200 nm.

[1] T.H. Loeber, D. Hoffmann and H. Fouckhardt, Proc. SPIE 79470N (2011) [2] J. Strassner, J. Richter, T.H. Loeber and H. Fouckhardt, Proc. SPIE 92880F (2014) [3] H. Fouckhardt et al., J. Cryst. Growth, 404, 48-53 (2014) *Contact: [email protected]

Fig. 1: a) Scanning electron microscope (SEM) images of highly ordered QDs. The dots grow in the milled holes. b) SEM image of the edge of the array of holes. On the left side the QDs grow randomly on the plane part of the buffer layer. On the right hand side they grow highly ordered in the holes on the pre-structured GaAs buffer layer.


P8

Beating 1/r²: cylindrical crucibles for large working distances

Wolfgang Braun *

ivac UG (haftungsbeschränkt), Weingartweg 12, 74321 Bietigheim-Bissingen, Germany

Due to the straightforward physics ofMBE (low working pressures, large meanfree paths), the flux distribution of effusionsources can be calculated with highaccuracy and reasonable effort using MonteCarlo algorithms [1] that are based on twoassumptions: i) no interaction of theparticles in the gas phase, ii) cosine lawreemission from hot surfaces (cruciblewalls).

I use such calculations to study thedeposition characteristics of long, cylindricalcrucibles. The example shown in the figureshows the flux distribution (layer thicknessin the substrate plane) of such a crucible asa function of its filling level, from full (top) toalmost empty (bottom). The chosengeometry corresponds to a 160 mm longcrucible with 14 mm inner diameter and aworking distance of 240 mm at an angle of21°.

The results show a strong variation of theflux distribution with a dramatic focusingeffect for low filling levels. The best materialutilization is achieved for the largestdistance from the melt to the substrate,suggesting a pathway to optimize thesource geometry for MBE systems withsmall sample sizes. Choosing a cruciblewith a constant cross section similar to thesample size, large working distances allowfor a large number of effusion sources at asmall angle to the substrate normal, leadingto excellent flux uniformity. Long crucibleswith a low filling level focus the material thatwould otherwise spread into a wide coneonto the sample, with excellent materialutilization of the expensive source materialsand low parasitic coverage of the chamberwalls. This translates into extendedcampaign times.

The longer crucibles of such designsrequire longer heaters in the effusionsources. However, as the power dissipation

of effusion sources, at least at elevatedtemperatures, is dominated by the radiationlosses through the crucible orifice, theoverall power budget of such an MBEsystem is not dramatically affected.

On the other hand, smaller source anglesto the substrate normal allow the design ofchambers with smaller outer diameter andtherefore smaller footprint, in addition totheir smaller volume and inner surface andtherefore better vacuum with the samepumping system.

[1] Z.R. Wasilewski, G.C. Aers, A.J. SpringThorpe, C.J. Miner, J. Vac. Sci. Technol. B 9, 120 (1991).


Fig. 1: Flux distributions in the sample plane asa function of crucible length vs. diameter, orfilling level, for a long, cylindrical crucible


P9

CVD growth of atomically thin MoS2 films for digital electronics

D. K. Polyushkin 1*, S. Wachter 1, O. Bethge2, and T. Mueller 1

1 Vienna University of Technology, Institute of Photonics, Gusshausstrasse 27-29, 1040 Vienna, Austria

2Vienna University of Technology, Institute of Solid State Electronics, Floragasse 7,1040 Vienna, Austria

Two-dimensional (2D) materials receive

a great interest because of their unique properties. Molybdenum disulfide (MoS2) is probably the most prominent member of the large group of transition metal dichalcogenides (TMDs) belonging to even larger family of 2D materials. Due to immunity to short-channel effects, mechanical flexibility and improved electrostatic gate control, 2D MoS2 is a promising candidate for modern electronics [1], [2].

To achieve fabrication of complex electronic circuits on 2D materials one has to synthesize uniform films on a large scale. One of the well-established techniques is chemical vapor deposition (CVD). In this work, we utilize CVD growth to synthesize cm2 scale single- and few-layer continuous MoS2 films with high uniformity. The growth recipe is adopted from [3]. The films are grown from MoO3 and sulphur precursors in tube CVD furnace at 700oС in argon environment at atmospheric pressure on c-plane sapphire substrates.

We used our films to fabricate logic building blocks and logic circuits from single- and few-layer MoS2 transistors. One of the recent circuitry we fabricated is a 1-bit implementation of a microprocessor [4]. Our processor consists of 115 transistors and is based on the NMOS logic family. It incorporates a program counter to facilitate program flow, several registers used to store I/O-data, an arithmetic logic unit performing the actual operations and a control unit coordinating the function of the other subunits. It is able to run simple, user defined programs that consist of logical operations and are stored in an external memory. By varying the W/L ratios of the FETs we were able to fabricate logic gates that are easily cascadable into larger, more complex circuits.

Fig. 1: Schematic of the CVD tube furnace

with AFM image of the bare sapphire substrate and the optical microscope images of the grown films on the wafer. On the edge of the grown film triangular shape grains are formed, which then coalesce into continuous film towards the center of the wafer. On the bottom, optical microscope image shows 1-bit microprocessor, consisting of 115 transistors.

A short program of 10 instructions was

executed, confirming the correct rail-to-rail operation of our processor. It constitutes the most complex logic device using 2D-semiconductors fabricated to date [5] and is readily scalable to multi-bit data.

[1] B. Radisavljevic, et al. ACS Nano, vol. 5, no. 12,

pp. 9934–9938, 2011. [2] G. Fiori et al., Nat. Nanotechnol., vol. 9, no. 10, pp.

768–779, 2014. [3] D. Dumcenco et al., ACS Nano, vol. 9, no. 4, pp.

4611–20, Apr. 2015. [4] S. Wachter, et al. Nat. Commun., vol. 8, p. 14948,

Apr. 2017. [5] L. Yu et al., Nano Lett., pp. 6349–6356, 2016. *Contact: [email protected]


P10

Ring Quantum Cascade Lasers: Versatile Light Emission and Applications in Spectroscopic Sensing

R. Szedlak*, M. Holzbauer, A. Harrer, B. Schwarz, D. MacFarland, T. Zederbauer,

H. Detz, A. M. Andrews, W. Schrenk and G. Strasser

Institute of Solid State Electronics & Center for Micro- and Nanostructures, TU Wien

Quantum cascade lasers (QCLs) are compact and versatile light sources emitting in the mid-infrared and terahertz spectral range. Therefore, QCLs are popular light sources for spectroscopy and chemical fingerprinting.

Ring QCLs [1] consist of a ring-shaped waveguide with a second order distributed feedback (DFB) grating on top. The latter selects the lasing mode and provides vertical light emission. Due to the relatively large emitting area, these lasers provide a strongly collimated emission beam.

We present several techniques for efficient light extraction from these ring QCLs including integrated phase shifts [2]and metamaterial-induced manipulation of the substrate-emitted light [3] as shown in Fig. 1 and 2, respectively.

Fig. 1: Scanning electron microscope (SEM) image of a ring QCL with a dual grating forming a continuous π-phase shift grating. [2]

Fig. 2: SEM image of a gradient-index meta-material fabricated on the substrate side of a ring QCL for on-chip light collimation. [3]

In the last years, these lasers have proven to be mature and reliable light sources, suitable for spectroscopic applications. In combination with bi-functional quantum cascade hetero-structures [4], ring QCLDs are utilized for compact on-chip gas sensor systems [5,6]as shown in Fig. 3.

Fig. 3: Sketch and SEM image (inset) of an on-chip ring QCLD gas sensing system. [6]

This sensor concept combines surface-emitting and –detecting elements on asingle-chip and paves the way for compact hand-held quantum cascade gas sensors.

[1] E. Mujagic et al., Appl. Phys. Lett. 93, 011108 (2008).[2] R. Szedlak et al., Sci. Rep. 5, 16668 (2015).[3] R. Szedlak et al., Appl. Phys. Lett. 104, 151105 (2014).[4] B. Schwarz et al., Appl. Phys. Lett. 101, 191109 (2012).[5] A. Harrer et al., Sci. Rep. 6, 21795 (2016).[6] R. Szedlak et al., ACS Photonics 3, 1794 (2016).



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P11

Influence of boron incorporation in GaAs nanowires grown by self-catalysed MBE

Suzanne Lancaster 1*, Heiko Groiss 2, Tobias Zederbauer1, Donald MacFarland1,

Aaron Maxwell Andrews1, Werner Schrenk1, Gottfried Strasser1, and Hermann Detz 1,3

1 Center for Micro- and Nanostructures TU Wien, 1040 Vienna, Austria

2 Center of Surface & Nanoanalytics, Johannes Kepler University, 4040 Linz, Austria3 Austrian Academy of Sciences, 1010 Vienna, Austria

Boron arsenide is a relatively little studied semiconductor with a small lattice constant of 4.78Å. This makes the growth of ternaries such as BxGa1-xAs interesting for strain engineering, since no other III-arsenides cover the same range of lattice constants. However, growth with B is a challenge and has been seen to lead to surface segregation [1] and unintentional doping due to antisite defects [2].

To that end, the incorporation of boron in GaAs nanowires (NWs) was investigated via the growth of GaAs/B:GaAs heterostructure nanowires. GaAs NW stems were grown for 18 minutes via a self-catalysed method, followed by 42 minutes of growth where all parameters were kept constant and in addition boron was supplied from a water-cooled high-temperature effusion cell. The source material was powdered boron of 6N purity, and the BAs growth rate was assumed to be proportional to the cell temperature, as we previously found for layer growth [1].

Figure 1 shows the length distributions of nanowires grown at two different cell temperatures. For comparison, the average length of GaAs nanowires grown for the same total length of time (1 hour) is indicated. Although SEM images indicated the nanowires formed well (inset fig. 1), it is clear that axial nanowire growth was suppressed.

Through post-growth transmission electron microscopy (TEM) analysis of the NWs we found that on all NWs the Ga catalyst droplet had been completely consumed, with a characteristic crystal phase switch from the zinc-blende (ZB) crystal structure of the main NW to wurtzite (WZ) (figure 2). This leads us to hypothesise that the observed reduction in axial growth is due to unintentional droplet

consumption leading to sidewall deposition.We propose that this droplet

consumption results from either a reduction in the diffusion length of Ga adatoms in the

presence of B, or to parasitic heating due to the high-temperature B cell, leading to ahigher As4 flux. This has potential implications for the epitaxial MBE growth of all III-V materials containing boron.

[1] H. Detz et al., J. Cryst. Growth (2017)[2] H. Dumont et al, Appl. Phys. Lett. 82, 1830 (2003)


Fig. 1: Histogram of NW lengths for two B:GaAs samples. Average GaAs NW length is indicated for comparison. Inset: SEM image of B:GaAs NWs

Fig. 2: HRTEM image of consumed droplet. Areas of stacking faults (SFs) and WZ crystal structure are indicated.


P12

Bi-functional Quantum Cascade Detectors/Lasers

M. Beiser1*, B. Schwarz 1, A. Harrer 1, M. Holzbauer 1 H. Detz 3, A.M. Andrews1, G. Strasser1, 2

1 Institute for Solid State Electronics and Center for Micro- and Nanostructures, TU Wien,

Floragasse 7, 1040 Wien, Austria2Center for Micro and Nanostructures, TU-Wien, Floragasse 7, 1040 Wien, Austria

3 Austrian Academy of Sciences, Dr. Ignaz Seipel-Platz 2, 1010 Wien, Austria

The recent straightforward implementation of a bi-functional QCLD opened the gate widely for new concepts of on-chip detection in the mid-infrared [1]. The mid-infrared is very interesting as the fundamental absorption lines of molecules like water and carbondioxide lie in there. Also the recent development of an integrated structure with an watt-level output power lever at room temperature increases the attractivity for chemical and biological sensing. An example for such a structure is displayed in figure 1 on the right.Another way to implement the on-chip concept, is the use of a surface emitting ring QCL with an integrated detector [2]. A prototype for this was tested with isopropanol and water and showed a detection limit of 50 ppm.The link to epitaxial growth for Bi-functional devices is the quality of the layers for the QCL. The improvement of the layer quality needs optimization of band-structure and wavefunction modeling and also advanced processing of fabrication and epitaxial regrowth [3], [4].In this contribution it will be displayed, how the recent progress has evolved and how it is connected to improvement of MBE techniques. The possible outlook of thisrecent developments is the implementationof frequency combs on an on-chip device.

[1] B. Schwarz, C.A. Wang, L. Missaggia, T.S. Mansuripur, M.K. Connors, D. McNulty, J. Cederberg, G. Strasser, and F. Capasso, ACS Photonics 2017 4(5), 1225-1231.[2] A. Harrer, R. Szedlak, B. Schwarz, H. Moser, T. Zederbauer, D. MacFarland, H. Detz, A.M. Andrews, Bernhard Lendl, W. Schrenk, and G. Strasser, Sci. Rep., 107, 6:21795 (2016).[3] C.A. Wang, B. Schwarz, D. Siriani, , L. Missaggia, M.K. Connors, T. Mansuripur, D. R. Calawa, D. McNulty, M. Nickerson, J.P. Donnelly, K. Creedon and F. Capasso, IEEE Q. Elec.., 23, No. 6 (2017).[4] C.A. Wang, B. Schwarz, D. Siriani, M. Connors, L. Missaggia, D. Calawa, D. McNulty, A. Akey, M.C. Zheng, J.P. Donnelly, T. Mansuripur, F. Capasso, IEEE J.o. Crystal Regrowth, 464, 215-220 (2016).


Fig. 1: SEM Image of a DFB laser, a DLSPP waveguide and the detector unit building a bi-functional device


P13

The polarization of ring interband cascade lasers

M. Holzbauer 1*, R. Szedlak 1, H. Detz 2 , R. Weih 4, S. Höfling 3,4,

W. Schrenk 1, J. Koeth 4, and G. Strasser 1

1 Institute of Solid State Electronics and Center for Micro- and Nanostructures,

Technische Universität Wien, A-1040 Wien, Austria2 Österreichische Akademie der Wissenschaften, A-1010 Wien, Austria

3 Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, D-97074, Germany

4 nanoplus Nanosystems and Technologies GmbH, D-97218 Gerbrunn, Germany

The interband cascade laser (ICL) [1,2] is a hybrid between conventional photodiodes and quantum cascade lasers. Thus it combines the long carrier lifetimes of bandgap diodes with the carrier recycling scheme utilized in intersubband cascading lasers. Due to the semimetallic interface between InAs and GaSb, electrons and holes are generated internally. Carriers are recycled via interband tunneling from the valence to the conduction band. This allows achieving differential quantum efficiencies greater than one. Or in other words, each injected carrier can emit multiple photons. The low input power required for lasing makes the ICL an ideal candidate [3] for mobile applications with low power consumption.

We present an ICL fabricated into a ring shaped cavity. A second-order distributed feedback grating is used to couple the light out in vertical direction. The grating is etched into the uppermost cladding layers and completely covered by a gold metallization. In this configuration the generated light is diffracted towards the GaSb substrate. For a device with 400µm outer diameter and 10µm waveguide width, we measured a pulsed threshold current density <1kA/cm² at room temperature. The ring ICL emits at a wavelength ~3.7µm. The recombination across the bandgap between states in the conduction band and empty states in the heavy-hole valence band dominate the polarization selection rule for quantum well structures. Therefore the gain in ICLs favors TE polarized light. We expect a different radiation pattern compared to

previous results on ring quantum cascade lasers [4]. Fig.1 (a)-(c) shows the measured nearfields on the substrate-side of the ring ICL. If a polarizer is inserted between the laser and the bolometer camera, the electric field is blocked in the direction parallel to the wire grid. From measurements with different rotation states of the polarizer we conclude that the electric nearfield of the ring ICL has a radial orientation, as shown in Fig.1 (d).

Fig.1: (a) Unpolarized nearfield measured with a bolometer camera. (b) Vertical orientation of the wire grid. (c) Horizontal orientation and (d) resulting polarization of the electric field.

[1] R. Q. Yang, Superlattices Microstruct. 17, 77 (1995)[2] I. Vurgaftman, R. Weih, M. Kamp, J. R. Meyer, C. L. Canedy, C. S. Kim, M. Kim, W. W. Bewley, C. D. Merritt, J. Abell and S. Höfling, J. Phys. D: Appl. Phys.48, 123001 (2015).[3] R. Weih, L. Nähle, S. Höfling, J. Koeth, and M. Kamp, Appl. Phys. Lett. 105, 071111 (2014).[4] R. Szedlak, M. Holzbauer, D. MacFarland, T. Zederbauer, H. Detz, A.M. Andrews, C. Schwarzer, W. Schrenk, and G. Strasser, Sci. Rep. 5, 16668 (2015)



P14

Single Period Quantum Cascade Detector

B. Schwarz 1*, P. Reininger1, A. Harrer 1, D. MacFarland1, H. Detz3, A.M. Andrews1, W. Schrenk2 and G. Strasser1,2

1 Institute of Solid State Electronics, TU-Wien, Floragasse 7, 1040 Wien, Austria

2 Center for Micro and Nanostructures, TU-Wien, Floragasse 7, 1040 Wien, Austria3 Austrian Academy of Sciences, Doktor-Ignaz-Seipel-Platz 2, 1010 Wien, Austria

Quantum cascade detectors (QCD) were under extensive investigation during the past years. Their room temperature operation properties, operation speed and integration to bi-functional quantum cascade laser detector [1] structures results in a variety of promising applications.

Typically a standard quantum cascade detector active region design consists of 20 up to 40 periods. For 45° polished facet mesa geometries, this is a good trade-off between the reachable responsivity and the differential resistance.

With a high resistance active region design, the number of periods can be reduced to increase the responsivity and maintain a high differential resistance of the device. This approach is efficient utilizing absorber structures which compensate for the lower absorption of the active zone as a result of the low number of periods. A straight forward geometry which can be used, is a facet illuminated ridge with the active zone embedded into a dielectric low loss waveguide.

The ridge waveguide offers a long absorption length and thereby high absorption. A highly doped substrate prevents light coupling only to the front facetof the ridge. With a single period active region and the ridge coupling scheme a responsivity as high as 0.86A/W at room temperature with an external quantum efficiency of 25% (without ARC) could be shown. The specific detectivity obtained is 7,2x107Jones at 300K for the operation wavelength at 4.1µm [2].

These results show a significant improvement over previously reported QCD performance and provides a model for the performance limits of QCDs.

[1] B. Schwarz, D. Ristanic, P. Reininger, T. Zerderbauer, D. MacFarland, H. Detz, A.M. Andrews, W. Schrenk and G. Strasser, Appl. Phys. Lett. 107, 071104 (2015)

[2] B. Schwarz, P. Reininger, A. Harrer, D. MacFarland, H. Detz, A.M. Andrews, W. Schrenk and G. Strasser, Appl. Phys. Lett., 111, 061107 (2017).


Fig. 1: Single period active region with a mini gap to prevent carrier losses and a mini band for efficient carrier injection to the ground level.


P15

Asymmetry study for high performance InGaAs/InAlAs terahertz quantum cascade lasers

M. A. Kainz1,3*, C. Deutsch1,3, M. Krall1,3, S. Schönhuber1,3, H. Detz3,4, T. Zederbauer2,3, D. C. MacFarland2,3, A. M. Andrews2,3, W.Schrenk3,

G. Strasser2,3, and K. Unterrainer1,3

1Photonics Institute, TU Wien, Gußhausstraße 27-29, 1040 Vienna, Austria

2Institute of Solid State Electronics, TU Wien, Floragasse 7, 1040 Vienna, Austria 3Center for Micro- and Nanostructures, TU Wien, Floragasse 7, 1040 Vienna, Austria

4Austrian Academy of Sciences, Dr. Ignaz Seipel-Platz 2, 1010 Vienna, Austria

Quantum cascade lasers (QCLs) are powerful sources of coherent radiation covering the frequency range from mid-infrared to terahertz. In the terahertz frequency range the active region is normally realized using a GaAs/AlxGa1-xAs semiconductor heterostructure. This material system enables a variable conduction band offset by changing the Al-content in the barrier layers without introducing a significant lattice mismatch between the barrier and well material. In comparison to the standard GaAs-based material system, active regions based on material systems with a lower effective electron mass are highly beneficial for the design of terahertz QCLs as the optical gain increases for a lower effective electron mass [1]. Promising material systems are based on InGaAs or InAs with an effective electron mass of 0.043 and 0.023, respectively, compared to that of GaAs (0.067) [2, 3].

In this work we present a systematic study of growth related asymmetries for terahertz QCLs based on the InGaAs/InAlAs material system lattice matched on InP [4]. A nominally symmetric active region enables the comparison of the positive and negative bias direction of the very same device. With such bias dependent performance measurements asymmetries like dopant migration and interface roughness, which play a crucial role in this material system, are studied and result in a preferred electron flow in growth direction. A structure based on a three well optical phonon depletion scheme is optimized for this bias direction. Depending on the doping concentration the performance of the QCLs shows a trade-off between maximum

operating temperatures and high output powers. While a peak output power of 151 mW is achieved for a sheet doping density of 7.3 x 1010 cm-2, the highest operation temperature of 155 K is found for 2 x 1010 cm-2. By further attaching a hyperhemispherical GaAs lens to a laser facet, the peak output power could be improved and reaches a record output power for double metal waveguide terahertz QCLs of almost 600 mW.

[1] E. Benveniste, et al., Appl. Phys. Lett. 93, 131108(2008). [2] M. Fischer, et al., J. Cryst. Growth 311, 1939 (2009). [3] M. Brandstetter, et al., Appl. Phys. Lett. 108, 11109 (2016). [4] C. Deutsch, et al., ACS Photonics 4, 957 (2017)


Fig. 1: Bandstructure of the symmetric active region and laser performance for different sheetdoping densities.


P16

High Power THz Quantum Cascade Lasers

Sebastian Schönhuber1, Martin Brandstetter1, Christoph Deutsch1, Michael Krall1, Martin A. Kainz1, Hermann Detz3, Donald C. MacFarland2, Aaron M.

Andrews2, Werner Schrenk2, Gottfried Strasser2, and Karl Unterrainer1

1Photonics Institute, Vienna University of Technology, Gusshausstrasse 25-29, A-1040 Vienna, Austria

2 Institute of Solid State Electronics, Vienna University of Technology, Floragasse 7, A-1040 Vienna, Austria

3 Austrian Academy of Sciences, Dr. Ignaz Seipel-Platz 2, 1010 Vienna, Austria

E-mail address: [email protected]

The terahertz (THz) spectral region is of particular interest for numerous applications relying on the unique properties of many materials at these frequencies. Quantum cascade lasers (QCLs) are compact, electrically driven sources, able to emit coherent radiation in this spectral region. One particular feature of THz QCLs is the high output power, which makes THz QCLs highly interesting candidates for future applications like remote sensing and imaging [1,2]. So far, the maximum operation temperature of these devices is limited to about 200 K, which necessitates cryogenic cooling for operation.

To achieve the highest peak output powers, so-called semi-insulating surface plasmon (SISP) waveguides are commonly used, where the mode is confined between a top metal layer and a semi-transparent, highly doped semiconductor layer on the bottom. One drawback of this technique is acomparably low maximum operation temperature, which can be attributed to the low confinement of the optical mode within the active region. To address this issue, we increased the number of cascades in the active region and thus also the waveguide thickness, which leads to an improved confinement of the optical mode within the active region. Furthermore, more light is generated due to an increased active region volume. Since the growth of the active region is typically performed by molecular beam epitaxy (MBE), fabricating thicker structures would require unreasonable long time. Thus, we make use of a direct wafer bonding technique to stack two equal active regions of regular thickness on top of each other [3].

In Fig. 1 the fabrication of a wafer bonded terahertz QCL with SISP waveguide is illustrated. The upper active region is flipped upside down and bonded on top of the lower one. For an applied bias voltage,

he electrons move in growth direction in one sub-stack, and against it in the other one.

Thus, the active region needs to show the same operation characteristics in

Fig. 1 Illustration of a stacked actrive region with SISP waveguide.both bias directions in terms of threshold current and gain spectrum. Previous experiments showed that a symmetric bandstructure alone would not lead to symmetric transport and performancebehavior [4]. We thus had to compensate for growth-related asymmetries, which are identified to be due to dopant migration in the used GaAs/AlGaAs material system. The fabricated devices show a two-facet peak optical output power of 0.94 W at 5 K, and still more than 0.6 W at 70 K [5]. The device furthermore shows a comparably high maximum operation temperature of 122 K. In principle, even more active regions can be stacked on top of each other, which would further increase the output power, the confinement factor and thus the overall device performance.

[1] A. W. M. Lee, et al., Appl. Phys. Lett. 89, 141125 (2006).[2] M. I. Amanti, et al. (2012).[3] M. Brandstetter, et al., Opt. Express 20, 23832 (2012).[4] C. Deutsch, et al., Appl. Phys. Lett. 102, 201102 (2013).[5] M. Brandstetter, et al., Appl. Phys. Lett. 103, 171113

(2013).


P17

Inverse Bandstructure Engineering of Alternative Barrier Materials for InGaAs-based Terahertz Quantum Cascade Lasers

B. Limbacher1,3,*, M. Krall1,3, M. A. Kainz1,3, M. Brandstetter1,3, C. Deutsch1,3, D.

C. MacFarland2,3, T. Zederbauer2,3, H. Detz2,3, A. M. Andrews2,3, W. Schrenk3, G. Strasser2,3 and K. Unterrainer1,3

1 Photonics Institute, TU Wien, Gusshausstraße 27-29, A-1040 Vienna, Austria

2 Institute of Solid State Electronics, TU Wien, Floragasse 7, A-1040 Vienna, Austria 3 Center for Micro- and Nanostructures, TU Wien, Floragasse 7, A-1040 Vienna, Austria

Quantum cascade lasers (QCLs) are compact and powerful sources that cover a wide spectral range from infrared to terahertz (THz) radiation. The emission characteristics of QCLs depend on design parameters such as layer thickness, material composition and doping. Therefore, the material system has to be chosen accurately. Most commonly used material systems for THz QCLs are GaAs/AlGaAs and InGaAs/InAlAs. The latter requires very thin layers of InAlAs and is therefore difficult to manufacture epitaxially [1]. One solution to overcome this issue, while still making use of the benefits provided by InGaAs, namely lower effective electron mass (m*= 0.043m0) which leads to a higher optical gain, is the usage of different barrier materials such as the ternary GaAsSb [2] and the quaternary InAlGaAs [3]. Crucial for the barrier thickness is the conduction band offset (CBO) of the material system. The common notion is to employ barrier materials having lower CBOs and therefore thicker barriers.

We implemented an inverse quantum engineering algorithm [4] to investigate the influence of the barrier material on the lasing performance and characteristics of THz active regions. Starting from an original design, barrier materials are exchanged while the wave functions are kept constant. A systematic comparison between material systems such as InGaAs/InAlAs, InGaAs/GaAsSb and InGaAs/InAlGaAs was performed with focus on quantum transport and optical gain. Fig. 1 shows the quantum design with the wave functions, the electrical and the optical properties of two InGaAs-based devices, one of which is employs ternary InAlAs barriers, whereas the other device employs quaternary

InAlGaAs barriers. As designed, the algorithm leads to almost identical wave functions for different barrier thickness due to the different CBOs of the investigated materials. We find that thin barrier devices employing ternary barrier materials such as InAlAs show the highest optical gain. Consequently, the InGaAs/InAlAs material system, which is already commonly used for mid-infrared QCLs, is also very well suited for high performance THz QCLs. [1] M. Fischer, G. Scalari, Ch. Walther and J. Faist, J. Cryst. Growth , 311, 1939-1943 (2009). [2] C. Deutsch, H. Detz, T. Zederbauer, M. Krall, M. Brandstetter, A. M. Andrews, P. Klan, W. Schrenk, G. Strasser and K. Unterrainer, J. Infrared Millim. Terahertz Waves, 34, 374-385 (2013) [3] K. Othani, M. Beck, G. Scalari and J. Faist, Appl. Phys. Lett. 103, 041103 (2013) [4] I. Waldmueller, M. C. Wanke, M. Lerttamrab, D. G. Allen and W. W. Chow, IEEE J. Quantum Electron, 46, 1414-1420 (2010) *Contact: [email protected]

Fig. 1: Scaling of a resonant-phonon active region from ternary (a) InAlAs to quaternary (b) InAlGaAs barriers, while the wave functions stay almost identical.

(a)

(b)


P18

Understanding layers, nanowires and nanodots better on a lab multipurpose diffractometer

Z. Bao 1*, M. Gateshki1, L. Grieger1, J. Woitok1

1 PANalytical B.V., Lelyweg 1, 7602EA Almelo, The Netherlands

Investigating the structural property of

the engineered low dimensional materials such like layers, nanowires and nanodots is one of the basic tasks before proceeding for further studies. Conventional characterization techniques such as X-ray reflectivity, X-ray diffraction and reciprocal space mapping, etc., can provide a great deal of information to discriminate the polymorphism, determine composition and strain profiles, quantify thickness, density, surface and interface morphology, understand grain/crystalline size and distribution, estimate residual stress and degree of relaxation, know the preferred orientation for polycrystalline layer or epitaxial relationship for single crystal like high quality epitaxial layer. However, due to certain properties of the grown material, classic investigation methods can meet its limit. For example, analyze the residual stress on a highly-textured layer is often challenged by the accuracy; understanding the surface structural ordering of the nanowires and nanodots needs a new approach. In this work, we present some alternative methods including X-ray reflectivity maps, ultra-fast reciprocal space map, multiple HKL-Chi tilt stress measurement and GISAXS that can tackle these challenges and provide a comprehensive insight towards structural characterizations.


Fig. 1 (a) Stress result of an highly textured ZnO layer. (b)X-ray reflectivity map and GISAXS result of a nanoporous layer. (c) GISAXS image of a Co nanofiber sample.


P19

Fabrication of quasi-Gaussian-shaped nanoholes by MBE local droplet etching

X. Zhang 1*, R. Keil 1, Y. Chen1, Y. Li1, F. Ding1, 2 and O. G. Schmidt 1, 3

1 Institute for Integrative Nanoscience, IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany

2 Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover, Germany 3 Material Systems for Nanoelectronics, Technische Universität Chemnitz, Reichenhainer Str.70, 09107,

Chemnitz, Germany

Nanoholes are of significant importance in the research of current nanotechnologies. For one thing, they are frequently used as the growth templates for quantum dots, nanowires, nanopillars and many other advanced nanoarchtectures [1]; for another, nanohole is an ideal platform for the research of photonic confinement in nanophotonics, and polariton trapping in the condensed-matter physics [2].

Fig. 1: The AFM images of the surface morphology of the MBE local droplet etched sample. a) the AFM image of a 10×10 um2 area; b) the AFM image a single nanohole; c) the depth profile of the single hole measured in Fig. 1(b).

The fabrications of nanoholes are generally achieved by lithographic, dry/wet etching, and focused ion beam (FIB) milling etc. Here we present the fabrication of quasi-Gaussian-shaped nanoholes by in-situ MBE local droplet etching method on the surface of III-V semiconductor wafers. The unique advantage of this technique is the compatibility with subsequent MBE growths.

The process starts with the generation of metallic droplets on the AlGaAs surface in Volmer-Weber growth mode by depositing several monolayer of Al at a temperature between 630 oC and 700 oC without As flux, subsequently an additional annealing step without As flux is followed to transfer Al metal droplet into nanoholes with the help of atomic diffusion [3].

The Atomic Force Microscopy (AFM) measurement shows that the hole density is around 2.3×107 cm-2 and hole depth is around 30 nm at the etching temperature of 630 oC, as shown in Fig 1. These holes have a depth of 30 nm and were surrounded by smooth sidewalls, In addition, these nanoholes have Gaussian-shaped profiles, as depicted in Fig 1(b-c). Highly efficient photon confinement can be achieved [4], if such holes could be introduced into a well-designed microcavity.

[1] Z. M. Wang, B. L. Liang, K. A. Sablon, and G. J. Salamo, Appl Phys Lett 90, 113120 (2007). [2] D. Urbonas, T. Stoferle, F. Scafirimuto, U. Scherf, and R. F. Mahrt, Acs Photonics 3, 1542 (2016). [3] C. Heyn, A. Stemmann, M. Klingbeil, C. Strelow, T. Koppen, S. Mendach, and W. Hansen, J Cryst Growth323, 263 (2011). [4] F. Ding, T. Stoeferle, L. J. Mai, A. Knoll, and R. F. Mahrt, Phys Rev B 87, 161116(R) (2013).



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Notes


P20

Pulsed laser deposition of In2O3 thin films on YSZ(111)

J. Hofinger1*, G. Franceschi1, M. Horký1,2, M. Riva1 M. Wagner1,3, and U. Diebold1

1Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10/E134, 1040 Wien, Austria 2CEITEC, Brno University of Technology, Purkynova 123, Brno 612 00, Czech Republic

3Friedrich Alexander University Erlangen Nürnberg, Egerlandstraße 3, 91058 Erlangen, Germany

In2O3 is a wide band-gap semiconductor and belongs to the class of transparent conductive oxides, which combine high electrical conductivity and optical transparency in the visible re-gion. Undoped In2O3 and especially Sn doped In2O3 find application in optoelectronic devices [1-2], e.g. flat panel displays, solar cells or organic light emitting diodes. Additionally, In2O3 changes its conductivity depending on exposure to oxidizing and reducing gases, which makes it an interesting candidate for gas sensing applications [3-5]. In many applications the interface to a different material, e.g., an organic layer or ambient conditions, plays a key role in the performance. This is characterized by the geometric arrange-ment and electronic properties at the surface, the reactivity towards gaseous species, the band alignment and conductivity within heterostructures. Thus, achieving a better understanding of the atomic-scale surface characteristics by investigating well-defined single-crystal model sys-tems is of paramount importance to optimize the functionality of devices. Recently, In2O3 single crystals were used to investigate with scanning probe techniques the precise atomic-scale structure of In2O3(111) surfaces, as well as its reactivity towards water [6]. Undoped In2O3 single crystals are not commercially available, and synthetically grown ones are usually very small, measuring only 1-2 mm in diameter. While the small size is not critical for scanning probe techniques, area averaging techniques such as TPD and XPS, require larger samples of homogeneous composition for qualitative and quantitative investigations of e.g., the reactivity of the surface and its electronic properties. Thus, larger single crystalline samples would allow the use of a variety of techniques for In2O3. To compensate for the lack of large In2O3 single crystals, we have prepared well-ordered and atomically flat In2O3(111) thin films, with a thickness of few hundreds of nanometers. The films were grown on Y-stabilized zirconia (111) substrates by pulsed laser deposition (PLD). Their structure, chemical composition and morphology were characterized by electron (RHEED, LEED) and x-ray diffraction (XRD), XPS, atomic-force microscopy (AFM), and scanning tun-neling microscopy (STM). By optimizing the growth parameters (temperature and oxygen background pressure) and investigating their effect on the film morphology and structure we could obtain In2O3(111) films exhibiting properties comparable to the best single crystalline samples available. Such films exhibit atomically-flat regions a few hundreds of nanometers wide, separated by hexagonal pit-like structures a few nanometers deep. XRD reveals that the structure of the films is relaxed to the bulk lattice of bixbyite In2O3 in the out-of-plane direction, with typical peak widths comparable to those of single-crystalline samples. These films appear to be promising candidates to be used as an equivalent replacement of In2O3(111) single crystals, allowing combination of atomic-scale surface-science analysis and investigation of the electronic structure of such surfaces via area averaging spectroscopic tech-niques, as well as characterization of their reactivity to different chemical species. [1] C. G. Granqvist, A. Hultåker, Thin Solid Films, 411, 1 (2002). [2] D. S. Ginley, H. Hosono, D. C. Paine (Eds.), Handbook of Transparent Conductors, Springer (2010). [3] H. Yamaura, et al., Sens. Actuators B: Chem., 36, 325 (1996). [4] T. Takada, K. Suzuki, M. Nakane, Sens. Actuators B: Chem., 13, 404. (1993) [5] A. Galdikas, Z. Martunas, A. Setkus, Sens. Actuators B: Chem., 7, 633 (1992). [6] M. Wagner, et al., Adv. Mater. Interfaces, 1, 1400289 (2014).



P21

Characterization of thin Boron layers grown on Silicon utilizing Molecular Beam Epitaxy for ultra-shallow pn-junctions

A. Elsayed 1*, J. Schulze 1,*

1Institute for Semiconductor Engineering, University of Stuttgart, Pfaffenwaldring 47, 70569

Germany

Given its desirable physical and electrical properties, for decades, Boron has been employed in many areas of research and industry [1]. Nowadays, used mainly in the semiconductor industry for the unique characteristics of its compounds and as a p-type dopant species by means of ionic implantation or epitaxy. In this work, the growth of nanometer thick layers of Boron on Sili-con and the use of these films for ultra-shallow pn-junction formation are pre-sented and discussed.

In this work, Molecular Beam Epitaxy is

utilized for the growth of Boron layers with nanometer thicknesses on Silicon (100) epi substrates (highly n-type doped Si (100) substrates with a slightly n-type doped top layer grown by means of chemical vapor deposition with a thickness of 3 µm) targeting the formation of ultra-shallow p+n--junctions.

The growth properties of these films are investigated for growth temperatures ranging from 500 °C to 700 °C as well as for the variation in deposition time and conse-quent layer thicknesses. Resultant layers are then utilized to fabricate p+n-n+-junction diodes for electrical characterization and evaluation. It will be shown, that the layer properties and device characteristics are mainly dependent on the temperature and duration of deposition.

Diodes fabricated with these junctions display very low saturation current densities (~ 10-8 A/cm2) typical for conventional deep-junctions although at a fraction of the thickness. The diodes also display low series resistance as well as high ideality factors (Fig.1). Furthermore, diodes fabricated with these junctions display very high reverse breakdown voltages with characteristic breakdown behavior (Fig.2).

Furthermore, the use of these ultra-

shallow contacts for ultra-thin emitter con-tacts for insulated-gate bipolar transistors (IGBTs) will be discussed.

[1] Golikova, O. A. (1979), Boron and Boron-based semiconductors. phys. stat. sol. (a), 51: 11–40. doi:10.1002/pssa.2210510102M. [2] J. Nishizawa, K. Aoki, and T. Akamine, “Ultrashallow, high doping of boron using molecular layer doping,” Applied Physics Letters, vol. 56, no. 14, pp. 1334–1335, 1990. [3] F. Sarubbi, T. L. M. Scholtes, and L. K. Nanver, “Chemical Vapor Deposition of α-Boron Layers on Silicon for Controlled Nanometer-Deep p+n Junction Formation,” Journal of Electronic Materials, vol. 39, no. 2, pp. 162–173, Feb. 2010. *Contact: [email protected]

-70 -60 -50 -40 -30 -20 -10 01E-15

1E-12

1E-9

1E-6

0.001

Cur

rent

[A]

Voltage Applied [V] Fig. 2: Reverse Breakdown Characteristics

-1.0 -0.5 0.0 0.5 1.01E-15

1E-12

1E-9

1E-6

0.001

Cur

rent

[A]

Voltage Applied [V]

Fig. 1: I-V Characteristics for different sized diodes

Increasing diode area

Ideality Factor


P22

Wetting and dewetting of metals by sputter-deposited zirconia

P. Lackner 1*, J.-I. J. Choi 1,2, U. Diebold 1 and M. Schmid 1

1 Institute of Applied Physics, TU Wien, Wien, Austria

2 Institute of Basic Science, KAIST, Daejeon, Republic of Korea

Zirconia (ZrO2) is a material commonly used as electrolyte in solid oxide fuel cells, in gas sensors or as high-k dielectric, but also as support for metal particles in catalysis. For metal particles supported by oxides, wetting effects can be a serious concern in applications. Under reducing reaction conditions, the oxides form thin films that encapsulate the metal particles. [1,2] This effect (known as strong metal-support interaction (SMSI) in the catalysis community) is usually limited to reducible oxides, where the ultra-thin wetting layer is formed by a substoichiometric oxide. However, zirconia, a material used in solid oxide fuel cells or as high-k dielectric, is considered non-reducible. Nevertheless, the same wetting and dewetting processes can be encountered, although the underlying process was until now unclear.

We have prepared few-layer-thick ZrO2 films on Rh or Pt single crystals. ZrO2 was deposited using a UHV-compatible home-built sputter source [3] (in 7 × 10-8

mbar O2 and 8 × 10-6

mbar Ar), and then post-annealed in O2 to form ZrO2 islands. The sputter source can deposit Zr with high purity and very good reproducibility.

When the ZrO2 films are annealed at high temperatures (> 600°C) in 10-6

mbar oxygen, dewetting is encountered, i.e., oxide islands form and the bare metal surface gets uncovered in between. Annealing in ultrahigh vacuum instead leads to a structure akin to Stranski-Krastanov growth, i.e.,

oxide islands with the metal in between covered by an ultra-thin oxide. XPS shows that the ZrO2 trilayer is stoichiometric [4], as expected for a non-reducible oxide, thus the reason for the observed dewetting must be different from the usual variation of oxide stoichiometry. We propose a new mechanism for this wetting effect, which is alloying between Zr and the metal, modifying the metal-oxide bonding.

[1] S. J. Tauster et al., Science 211, 1121–1125 (1981). [2] O. Dulub et al., Phys. Rev. Lett. 84, 3646 (2000). [3] P.Lackner et al., submitted [4] H. Li et al., J. Phys. Chem. C 119, 2462 (2015). *Contact: [email protected]

Fig. 1: Proposed mechanism of the SMSI effect for the non-reducible oxide ZrO2.


P23

Growth of SixGe1-x-ySny Structures with High Sn Content for Bandgap Investigation

D. Schwarz 1*, I. A. Fischer1, M. Oehme 1 and J. Schulze 1

1 Institute for Semiconductor Engineering, University of Stuttgart, 70569 Stuttgart, Germany

In recent years, there has been a lot of research on the integration of electronic and photonic functionality on one single chip. However, Si as most common semi-conductor is not suitable for photonic device applications due to its indirect bandgap. Therefore, one of the greatest challenges of current Group-IV research is to find a concept to integrate optoelectronic device functionality on chip. In this context, the ternary alloy SixGe1-x-ySny is a particularly interesting material to investigate. On one side it allows the decoupling of bandgap and lattice constant. This fact allows the lattice matched growth of SixGe1-x-ySny on Ge at a certain ratio of Si to Sn. Furthermore, the ternary alloy is predicted to become a direct bandgap semiconductor at specific compositions and strain [1].

A key issue for further research is the

knowledge of the compositional bandgap dependency of SixGe1-x-ySny. A common parameterization of the bandgap includes terms up to quadratic order in compositional parameters [2]. Here, the prefactors of the quadratic terms are the so-called bowing parameters. However, while the bowing parameters for Si1-xGex and Ge1-xSnx are well known, the previous results for the bowing parameter of Si1-xSnx show a huge discrepancy [2].

In our presentation, we will highlight the opportunities and challenges of growing lattice matched SixGe1-x-ySny structures with high Sn content. For this purpose, we grew two series of SixGe1-x-ySny layers with different composition. The layer growth on 4” substrates started with a 50 nm Si buffer, which was then overgrown with a 100 nm thick Ge virtual substrate. In order to fulfill the condition of lattice matching of the SixGe1-x-ySny layers to the Ge VS, we kept the ratio of Si to Sn fixed.

The first series ended with a 100 nm intrinsic SixGe1-x-ySny layer on top. The

MBE-grown layers were analyzed by x-ray diffraction (XRD), see Fig. 1, photo-luminescence spectroscopy (PL) and Rutherford back scattering (RBS) to get detailed information about the compositional dependency of the bandgap and the crystal quality.

For the second series, the intrinsic SixGe1-x-ySny layer was overgrown with 100 nm highly n-doped SixGe1-x-ySny. Afterwards, single mesa diodes were fabricated out of these layers to investigate the electro-optical performance of the diodes containing the SixGe1-x-ySny layers.

We present results of the material characterization as well as electrooptical device characterization results and discuss the impact of layer composition on bandgap parameters.

[1] P. Moontragoon, R. A. Soref and Z. Ikonic, Journal of Applied Physics 112, 073106 (2012); [2] T. Wendav et. al., Appl. Phys. Lett. 108, 242104 (2016); *Contact: [email protected]

Fig. 1: XRD pattern of SixGe1-x-ySny layers with different compostion


P24

Fabrication of ZnO-based Resonant Tunneling Diodes for Quantum Cascade Structures

Borislav Hinkov1,*, Daniela Ristanic1, Werner Schrenk1, Maxime Hugues2, Jean-

Michel Chauveau2 and Gottfried Strasser1

1Institute of Solid State Electronics and Center for Micro- and Nano-Structures, TU Wien, Floragasse 7, 1040 Wien, Austria

2Centre de Recherche sur l’Hétéro-Epitaxie et ses Applications, Centre national de la Recherche Scientifique (CRHEA-CNRS), Rue B. Gregory, F-06560 Valbonne Sophia Antipolis, France

The terahertz (THz) spectral range (λ ~30µm – 300µm) is also known as the “THz-gap” because of the lack of compact semiconductor devices. Various real-world applications would strongly benefit from such sources like trace gas spectroscopy orsecurity screening. A crucial step is the operation of THz-emitting lasers at room temperature.

Current devices, of which GaAs-based quantum cascade lasers (QCLs) are the most promising ones, lack significant improvements within recent years concerning their maximum operating temperature. They are limited by the parasitic, non-optical LO-phonon transitions(36meV in GaAs), being on the same orderas the thermal energy at room temperature (kT = 26meV). Promising candidates tosolve this problem include materials like ZnO with their larger LO-phonon energy(ELO = 72meV). To master the fabrication of ZnO-based QC structures, a high quality epitaxial growth is crucial together with awell-controlled fabrication process including(selective) ZnO/ZnMgO etching, and the deposition of low resistance ohmic contacts.

Our devices are grown on m-plane [10-10] ZnO-substrate by molecular beam epitaxy (MBE) and patterned by reactive ion etching (RIE) in a CH4-based chemistry into 100µm square MESAs. The CH4-process protects the mask by an amorphous carbon-layer, which increases the selectivity of the etching process [1].

Resonant tunneling diode structures are investigated in this geometry and are presented including different barrier- andwell-configurations. We extract contact resistances of 8e-5 cm2 for un-annealed Ti/Au contacts and an electron mobility of above 130cm2/Vs, both in good agreement with literature.

Demonstrating resonant electron tunneling in ZnO/ZnMgO structures is one of the crucial building blocks for a QCL.

[1] S.-W. Na, M. H. Shin, Y. M. Chung, J. G. Han, and N.-E. Lee, “Investigation of process window during dry etching of ZnO”, J. Vac. Sci. Technol. A 23, 898 (2005).


40 µm

SiNZnO

a) b)

Fig. 1: a) Typical ZnO MESA RTD structures after fabrication. B) Exemplary IV-curve of a 100 µm square MESA RTD structure at liquid nitrogen temperatures.


P25

Natural Superlattice Structures of Bi-Chalcogenide Topological Insulators grown by MBE and Controlled by Stoichiometry

S. Wimmer1*, J. Stangl1, H. Groiss2, M. Albu3, F. Hofer4, V. Holý5, D. Kriegner5,

O. Caha6, G. Bauer1 and G. Springholz1*

1 Institute of Semiconductor Physics, Johannes Kepler Universität, A-4040 Linz, Austria

2 Center of Surface and Nanoanalytics, Johannes Kepler Universität, A-4040 Linz, Austria3 Center of Electron Microscopy (ZFE), Steyrergasse 17-3, A-8010 Graz, Austria

4 Institute for Electron Microscopy and Nanoanalytics, TU Graz, Steyrergasse 17, A-8010 Graz, Austria5 Department of Condensed Matter Physics, Charles University, 121 16 Prague 2, Czech Republic

6 Department of Condensed Matter Physics, Masaryk University, 61137 Brno, Czech Republic

Bismuth chalcogenide compounds are out-standing materials because of their unique topological properties of their electronic band structure, making them an outstanding representative of topological insulators that exhibit a Dirac-like surface state that is spin polarized and topologically protected by time-reversal symmetry [1]. Moreover they are the best thermoelectric materials for power conversion applications. The bismuth chalcogenides Bi2Se3 and Bi2Te3 and their various alloys exhibit a complicated hexago-nal crystal structure, which basically con-sists of X-Bi-X-Bi-X (X=Se, Te) quintuple layers (QL) van der Waal bonded to each other. Deviation from the 2:3 stoichiometry, however, results in a wide range of homolo-gous superlattice structures, where the QL stacking is interrupted by insertion of Bi-Bi double layers (DL) or even septuple layers.

In this work, we present a systematic study on epitaxial growth and structural properties of various binary and ternary Bi-chalcogenide layers grown by molecular beam epitaxy on BaF2 (111) substrates. This includes Bi2Se3-δ and Bi2Te3-δ with different stoichiometric composition, as well as of ternary alloys were Bi is replaced by mag-netic (Mn) or non-magnetic (In, Sn) dopants.The crystal structure was investigated by high-resolution x-ray diffraction, scanning transmission electron microscopy and EXAFS measurements.

For MBE growth under low excess Se or Te conditions, we observed random incorpo-ration of Bi double layers, leading to a strong modification of the surface mor-phology (see Fig. 1 (a-d)) as well as crystal structure (e). Incorporation of more than 3%Mn induces the formation of X-Bi-X-Mn-X-

Bi-X (X=Se, Te) septuple layers whereas for In incorporation the usual quintuple layer stacking remains. From our data a general structure model is derived that explains the peculiar structure of the epilayers and the consequences on the electronic properties are discussed.

Figure1: (a-d) AFM images of 500 nm Bi2Se3-δlayers with the Se excess value δ determined by XRD. (e) STEM simulations and crystal structure of various BimSen phases in the )1001( plane.[1] X. L. Qi, S. C. Zhang, Rev. Mod. Phys., 83, 1057(2011).




Practical Information


Notes


List of Exhibitors


Aidam R. Fraunhofer-Institut IAF [email protected] Aisenbrey B. Universität Paderborn [email protected] Ames C. AIM Infrarot-Module GmbH [email protected] Andrews A. M. Technische Universität Wien [email protected] Bao Z. Panalytical B.V. [email protected] Beck M. ETH Zürich [email protected] Beiser M. Technische Universität Wien [email protected] Berl M. ETH Zürich [email protected] Birner S. nextnano GmbH [email protected] Boehm G. Technische Universität München, WSI [email protected] Böttcher J. Veeco Instruments GmbH [email protected] Braun W. ivac UG [email protected] Breuer S. Fraunhofer-Institut HHI [email protected] Bruder R. RIBER SA [email protected] Buesing G. VBS Sprl [email protected] Calabrese G. Paul-Drude-Institut für Festkörperelektronik [email protected] Chauveau J.-M. CNRS-CRHEA [email protected] Coomber S. Wafer technology LTD [email protected] Covre da Soçva S. F. Johannes Kepler University [email protected] Delgado C. R. IHP Innovations for high performance

microelectronics [email protected]

Deneke C. Universidade Estadual de Campinas [email protected] Detz H. Technische Universität Wien [email protected] Dimakis E. Helmholtz-Zentrum Dresden-Rossendorf [email protected] Elsayed A. Universität Stuttgart [email protected] Enke H. abcr GmbH [email protected] Falta J. Universität Bremen, Festkörperphysik [email protected] Fischer P. Dr. Gassler Electron Devices [email protected] Gassler G. Dr Gassler Electron Devices [email protected] Gaucher S. Paul-Drude-Institut für Festkörperelektronik [email protected] Geßler J. Veeco Instruments GmbH [email protected] Gornik E. Technische Universität Wien [email protected] Grashei M. Technische Universität München, WSI [email protected] Groiss H. Johannes Kepler Universität [email protected] Harrer A. Technische Universität Wien [email protected] Heiss M. Scienta Omicron GmbH [email protected] Hildebrandt E. Technische Universität Darmstadt [email protected] Hinkov B. Technische Universität Wien [email protected] Hofinger J. Technische Universität Wien [email protected] Holzbauer M. Technische Universität Wien [email protected] Huang H. Johannes Kepler Universität [email protected] Jendrzey A. Dr. Eberl MBE-Komponenten GmbH [email protected] Kainz M. A. Technische Universität Wien [email protected] Keil R. IFW Dresden [email protected] Kozak B. VIDEKO GmbH [email protected] Künzler T. MEWASA AG [email protected] Lackner P. Technische Universität Wien [email protected] Lamare B. AXT [email protected] Lange F. Leibnitz-Institut für Kristallzüchtung im

Forschungsverbund Berlin e.V. [email protected]

Lefebvre D. CNRS-CRHEA [email protected] Lenz R. EpiServe GmbH [email protected]

List of Participants


Lepsa M. I. Forschungszentrum Jülich, PGI-10 [email protected] Limbacher B. Technische Universität Wien [email protected] Lipfert F. Panalytical B.V. [email protected] McFarland D. C. Technische Universität Wien [email protected] Möller S. CreaTec Fischer & Co. GmbH [email protected] Musalek T. Brno University of Technology [email protected] Nicolosi D. SAES Getters S.p.A. [email protected] Nowak J. Veeco Instruments GmbH [email protected] Oehme M. Universität Stuttgart [email protected] Papaioannou E. Technische Universität Kaiserslautern [email protected] Pawlis A. Forschungszentrum Jülich, PGI-9 [email protected] Pejchal T. CEITEC [email protected] Persson T. Scienta Omicron GmbH [email protected] Polyushkin D. Technische Universität Wien [email protected] Prochaska L. Technische Universität Wien [email protected] Ranjbar R. Max-Planck-Institute Chemical Physics of Solids [email protected] Rduch P. Prevac [email protected] Reichl C. ETH Zürich [email protected] Reuter D. Universität Paderborn [email protected] Riedl, H. Technische Universität München, WSI [email protected] Röthlein P. Hiden Analytical/Vacua GmbH [email protected] Rugeramigabo E. P. Leibniz Universität Hannover [email protected] Ruhstorfer D. Technische Universität München, WSI [email protected] Schäffler F. Johannes Kepler Universität [email protected] Scharnetzky J. ETH Zürich [email protected] Schmidt J. Leibniz Universität Hannover [email protected] Schön S. ETH Zürich [email protected] Schönhuber S. Technische Universität Wien [email protected] Schrenk W. Technische Universität Wien [email protected] Schuler H. Dr. Eberl MBE-Komponenten GmbH [email protected] Schwarz D. Universität Stuttgart [email protected] Seifritz J. Mantis Deposition GmbH [email protected] Semtsiv M. Humboldt University Berlin - Physics [email protected] Strasser G. Technische Universität Wien [email protected] Straßner J. Technische Universität Kaiserslautern [email protected] Szedlak R. Technische Universität Wien [email protected] Teubner T. Leibnitz-Institut für Kristallzüchtung im

Forschungsverbund Berlin e.V. [email protected]

Thomson R. k-Space Associates, Inc. [email protected] Tschirky T. ETH Zürich [email protected] Valentin S. R. Ruhr Universität, Angewandte Festkörperphysik [email protected] Vogt A. Universität Freiburg [email protected] Volobuev V. Johannes Kepler Universität [email protected] Weber N.-E. Scienta Omicron GmbH [email protected] Wegscheider W. ETH Zürich [email protected] Wieligor M. Prevac [email protected] Wimmer S. Johannes Kepler Universität [email protected] Yuan X. Y. Johannes Kepler Universität [email protected] Zhang X. IFW Dresden [email protected] Zoer M. Demaco Holland B.V. [email protected]



Workshop VenueDirections to the workshop venueThe subway line U1 (red line), station „Taubstummengasse“ is the nearest station to the venue.

Use the exit „Taubstummengasse“, follow the Favoritenstraße along straight ahead until you the

Gußhausstraße. Then turn right, the entrance is situated a few metres ahead.

Check-In is on the left-hand side of the entrance, the auditorium EI9 (room code: CA EG 17) is on

the right.


Public TransportThe venue - Gußhausstraße 27-29, 1040 Vienna - is situated close to the city center and

is easy to reach by the subway U1 (red line), station „Taubstummengasse“, a few walking

minutes from the station.

It can also be reached through the tram lines 1, 62 and the Badener Bahn, from the stop

Paulanergasse.

General information on public transport in Vienna: www.wienerlinien.at

From the airport to the venue

With the CAT-line directly from the airport to the station Landstraße/Wien Mitte. Then

subway U4 (green line) in the direction of Hütteldorf for 2 stations until Karlsplatz, then 1

station with the U1 (red line) in direction of Oberlaa until Taubstummengasse.

Should you arrive by train at the main railway station, it is just 1 stop away (U1 in direction

of Leopoldau) from Südtiroler Platz/Hauptbahnhof!

Route map of the Vienna subway, trains and CAT-line from the airport:


Workshop DinnerWorkshop Dinner will be held on the 28th of September 2017 at one of the most reknown „Heurigen“ Martin Sepp in the historic quarter of Grinzing, where Vienna meets the Wienerwald. Traditionally, Viennese wine is being enjoyed at the Heuriger. The noble nectar is at the center of a number of events in traditional wine-growing locations in Vienna such as Stammersdorf, Grinzing or Sievering but also the center of town.

There will be a bus transfer from the workshop location to dinner and back.

The buses will leave at the Workshop at 18:30, dinner will begin at 19:00. The first bus back will depart at 21:30, the second at 22:00. The journey is about 30min. depending on traffic.

Address:Heurigenwirt Zum Martin SeppCobenzlgasse 341190 Wien - GrinzingTel. +43 1 320 32 33http://zummartinsepp.at/


Vienna SightsVienna at a glance

With its successful blend of imperial tradition and contemporary creativity, the Austrian capital has established itself as a major player in the global tourism market. Magnificent edifices, predominantly in baroque, historicism (“Ringstrasse”) and art nouveau styles, and the city’s grand scale cause you to forget that this is the capital of the small Republic of Austria with just under 8.5 million inhabitants.

The St. Stephen’s cathedral is the icon and center of Vienna. The locals call it “Steffl” and its walls bear witness to the lives of many famous musicians. The Schönbrunn Palace is a World Cultural Heritage site and Austria‘s most-visited sight. Visitors will find numerous attractions here, from a tour through the authentically furnished residential and ceremonial rooms of the Imperial Family in the palace, to the maze and the labyrinth in the gardens and a separate Children‘s Museum. The banks of the Danube Island are a sensation in Vienna and can be reached by the U1 (Donauinsel), U6 (Neue Donau) and U2 (Donaumarina and Donaustadtbrücke) underground lines.Vienna, City of Music – Traditional and Modern

Experience Vienna, the world’s capital of music, by tracing the footsteps of some of the famous composers who have lived and worked here: Ludwig van Beethoven, Alban Berg, Johannes Brahms, Anton Bruckner, Joseph Haydn, Franz Liszt, Wolfgang Amadeus Mozart, Arnold Schoenberg, Franz Schubert, Johann Strauss senior and junior (the son being a TU Wien alumni!), Richard Strauss, Antonio Vivaldi and many more.

Vienna boasts one of the world’s finest orchestras – the Vienna Philharmonic – as well as the Vienna Symphony Orchestra and several other orchestras and ensembles of note. An institution by the very definition of the word, the Staatsoper offers performances by leading international artists on almost 300 days of the year. Vienna’s second largest opera house, the Volksoper, offers a rich variety of stage performances, from opera to operettas, musicals, ballet, and contemporary dance.

The Musikverein is known to music lovers all over the world as one of the most illustrious concert halls of them all, where only the crème de la crème are invited to perform. The Golden Hall is probably the world’s most famous concert hall thanks to the worldwide broadcast of the Vienna Philharmonic’s annual New Year’s Day Concert. The Vienna Symphony Orchestra, the Vienna Chamber Orchestra and the Klangforum Wien are all resident at the Wiener Konzerthaus. The Vienna Boys’ Choir enchants music lovers the world over. The choir’s new state-of-the-art concert hall, MuTh, located next to the boys’ school and residences in the Augarten park, opened in 2012. A very special way to enjoy music is presented at the House of Music, a unique high-tech voyage of discovery into the phenomenon of music. A further attraction is the Mozarthaus Vienna which opened on Mozart’s 250th birthday – in his former residence at Domgasse.Visit www.oeticket.com for concert tickets.

Vienna, the city of fine arts


Yet it is not only the city’s imperial architecture that renders it a city of beauty. Vienna also boasts world-renowned museums, art collections and works of art. Close to the State Opera House, the Albertina houses the world’s largest collection of graphic art, spanning 60,000 drawings, some million prints and an extensive collection of photographic and architectural material. The Kunsthistorisches Museum Wien (Museum of Fine Arts) houses the world’s largest collection of paintings by Bruegel. Meanwhile numerous works by Gustav Klimt and Egon Schiele are exhibited at the Belvedere and the Leopold Museum. MuseumsQuartier, a cultural attraction of international standing located in the city center close to famous museums, opened in 2001. Key attractions include: the Leopold Museum (mentioned above), the mumok – Museum moderner Kunst Stiftung Ludwig Wien, Architekturzentrum Wien, and Kunsthalle Wien.

The Naschmarkt, Vienna’s multicultural fruit and vegetable market which also features a flea market every Saturday, has witnessed the emergence of an extraordinarily diverse gastronomic scene in its vicinity over the past years. During the summer, Viennese and tourists alike throng to Prater park with the famous Giant Ferris Wheel.

Nightlife

New clubs, bars and contemporary art spaces are springing up all over the Austrian capital – sometimes in the places you would least expect to find them. Although each location has its own distinctive identity they all manage to pull off a typically Viennese blend of tradition and innovation.

Visit www.falter.at for a daily guide to the city’s music and cultural life.

Shopping

The range of shopping options is particularly rich and diverse in Vienna’s historic first district. Here, the main – and most exclusive – shopping streets of Kohlmarkt, Graben and Kärntner Straße form a pedestrianized area, which is known locally as the Golden U. A few buildings down is the equally illustrious Meinl am Graben, with its delectable delicacies. Kärntner Straße is home to one of just a handful of department stores in the city. The nearby Ringstraßen Galerien is a spacious, indoor shopper’s paradise containing 70 shops and restaurants. Mariahilfer Straße, a street linking the historic center with Schönbrunn Palace, has been transformed into the city’s largest shopping street since the completion of the U3 underground line. It is also the city’s newest pedestrianized zone.

Coffee, Cake and Literature: The Viennese Coffeehouse

For visitors to the city it is an attraction, for locals a second home, and for artists and literati an institution: the Viennese Coffeehouse. Viennese coffeehouse culture was officially added to the UNESCO intangible cultural heritage list in 2011. Today, coffeehouses in Vienna are much more than just places to drink coffee – they are a way of life.

According to documentary evidence, the earliest Viennese coffeehouse was opened in the heart of the old town in 1685 at what is now Rotenturmstrasse 14. After the great lull in the coffeehouse tradition in the 1960s and 1970s, many cafés were restored to their former glory in the subsequent 20 years, including such well known establishments as Schwarzenberg at Kärntner Ring and Landtmann. Other old Viennese cafés reinvented themselves as contemporary espresso bars, much to the delight of the young and fashionable. For coffeehouse addresses please consult our homepage.


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Documents

Austrian MBE Workshop 2017 · 2017-09-21 · Austrian MBE Workshop 2017 A1 Thermal influence of interfaces in epitaxially grown superlattices M. Grashei, G. Böhm, R. Meyer and M.-C