Heraklion, 2014 Si/SiC Nanowire Growth by using Al Catalyst
Linsheng Liu
Slide 2
Heraklion, 2014 Outline Introduction - Motivation - Nanowire
Growth Mechanism - MBE (general, advantages for NW growth) Plan -
Measure the thickness of Al - Cluster study of Al film - Si
Nanowire Growth study - Si converted to SiC Nanowire -
Characterization
Slide 3
Heraklion, 2014 Problems Occur with Size Reduction 1.Expensive
manufacturing cost --- High defect densities --- Complicated
manufacturing techniques 2. Physical limitation 3. High power
dissipation
Slide 4
Heraklion, 2014 One possible solution: Nanowire FET bb 1.
Ultimate electrostatic control of channel(surround gate) 2.
Potential for lower power dissipation than MOSFET 3. Nanowires
allow the growth of axial heterostructures without the constraints
of lattice mismatch. This provides flexibility to create
heterostructures of a broad range of materials.
Slide 5
Heraklion, 2014 Interest in SiC NW FETs Combination of NWs and
SiC properties High-temperature sensors Field emission displays (as
cathodes) Biosensors High temperature (operating voltage) FETs SiC
NWFETs with increased operation temperature can substantially
increase packing density.
Slide 6
Heraklion, 2014 State of the art in SiC NW FETs (a) Shematic of
a SiC NWFET; (b) I-V characteristic of SiC nanowire FET for
different back gating from -40 to 40V. In the inset of (b) the
ID-VG charateristic is presented. --Rogdakis K et al.IEEE Trans.
Electron Devices, 2008, 55: 1970 Drawback: --The carrier
concentration is too high due to unintentional doping and low
crystalline quality of SiC NW, resulting in very low electron
mobility (16cm 2 V -1 s -1 ). Possible Solution: Use relatively
high cost methods(MBE or high purity CVD)
Slide 7
Heraklion, 2014 Our aim for growing SiC NWs 1.Grow Si NW by
using Al catalyst; 2.Convert to SiC NW; 3.Characterization;
4.Applications: SiC NWFET, high temperature sensor, field-emission
device;
Slide 8
Heraklion, 2014 First Approach : conversion of MBE-grown Si NWs
750C800C850C EDX-STEM EELS-STEM HAADF micrograph of a section of
nanowire of each sample. EDX line-scan is superimposed that
indicates the presence of C and Si together in the perimeter of the
sections. Semi-facetted sidewalls is show in octagonal shape in the
directions (2 0 0) and (1-1 1).. EELS spectra in the core and the
shell of the nanowire of each sample [1] E. Pippel, O.
Lichtenberger and J. Voltersdorf, J. Matt. Sci. Lett., 19, 2059
(2000) [1]
Slide 9
Heraklion, 2014 #A 100 nm #B 100 nm #C First Approach :
conversion of MBE-grown Si NWs-2 750C 800C850C
Slide 10
Heraklion, 2014 First Approach : conversion of MBE-grown Si NWs
750C of temperature seems to be enough to carburize regions of the
Si NW using MBE system. Carburization is demonstrated in a depth of
around 20nm. High temperatures seem to stimulate the generation of
staking faults. Conclusions:
Slide 11
Heraklion, 2014 V80S IESL-FORTH Nanowires growth by using MBE
1) Epitaxial growth under ultra-high vacuum and high pure sources
conditions, it is easy to obtain the clean surfaces, free of an
oxide layer; 2) Reflection high-energy electron diffraction(RHEED)
is a powerful in-situ characterization tool generally used in MBE,
which follows the crystalline evolution of nanowires in real time
during growth;
Slide 12
Heraklion, 2014 deposit Al on the substrate Create Al
cluster(Solid) by heating Supply suitable precursors(Vapor)
Al+precursor (Liquid) Supersaturation=> nanowire growth
alternating precursors => controllable nanowire heterostructures
nanowires can extend more than 20 micrometers in length Nanowire
Growth Process Al Seed Si Substrate SEM images: David Kohen, et al.
Phys. Status Solidi A, 2011(208): 2676-2680.
Slide 13
Heraklion, 2014 Vapor Liquid Solid Growth Model The
supersaturation of the metal-alloy catalyst is the main driving
force for nanowire growth 1 precursors direct impingement 2
desorption from the hut 3 diffusion from the sidewalls 4 desorption
from the sidewalls 5 diffusion from the substrate to the sidewalls,
6 diffusion from the sidewall to the drop 7 surface nucleation
Nucleation-mediated wire growth resulting in the vertical growth
rate V.G. Dubrovskii and N.V. Sibirev, Phys. Rev. B 2008
Slide 14
Heraklion, 2014 Phase Diagram of Al-Si (b)TEM and SAED pattern
--YEWU WANG, VOLKER SCHMIDT, STEPHAN SENZ AND ULRICH GOSELE,
Epitaxial growth of silicon nanowires using an aluminium catalyst,
Nature Nanotechnology, Vol1, December 2006, 186-189. (a) SEM Cross
sectional image; Advantage and Disadvantage: Si NW growth is under
VSS growth condition. The advantage is low Si solubility in Al
catalyst, if we grow Si-Ge heterostructure in this condition, the
interface will be sharp. The disadvantage is the growth rate is
very low.
Slide 15
Heraklion, 2014 Phase Diagram of Al-Si 2.SEM image of
Al-catalysed Si nanowire grown @600C. [1]Joonho Bae, et al, Journal
of Crystal Growth, 2008(310): 4407-4411. [2]David Kohen, et al,
Phys. Status Solidi A, 2011(208): 2676-2680. 1.SEM image of
Al-catalysed Si nanowire grown @950C.
Slide 16
Heraklion, 2014 Outline Introduction - Motivation - Nanowire
Growth Mechanism - MBE (general, advantages for NW growth) Plan -
Measure the thickness of Al - Cluster study of Al film - Si
Nanowire Growth study - Si converted to SiC Nanowire -
Characterization
Slide 17
Heraklion, 2014 Choice of the catalyst Au Advantages: physical
and chemical stability, low Eutectic temperature Drawbacks: act as
a deep level trap decrease carrier mobility, lifetime, diffusion
lengthavoid in standard IC techniques Al Advantages: compatible
with standard IC techniques, better optical properties Drawbacks:
oxidize quickly, need very clean deposition system
Slide 18
Heraklion, 2014 Binary phase diagram of Au-Si alloy and Al-Si
alloy
Slide 19
Heraklion, 2014 Al catalyst thickness Al: 1 to 10nm
Slide 20
Heraklion, 2014 Cluster study of Al Diameter of particles are
less than 20 nm SEM Images of Au Clusters on GaAs
Slide 21
Heraklion, 2014 State of the art of Al mediated Si NW Growth
(a) SEM Cross sectional image; (b)TEM and SAED pattern --YEWU WANG,
VOLKER SCHMIDT, STEPHAN SENZ AND ULRICH GOSELE, Epitaxial growth of
silicon nanowires using an aluminium catalyst, Nature
Nanotechnology, Vol1, December 2006, 186-189. There is very few
experimental result showing Si NWs grown by using Al with very low
density defects. Up to now, there is no group to use MBE grow Al
mediated Si NW. NWs grown under ultra-high vacuum and high pure
sources conditions in MBE will be helpful towards the aim of high
quality NWs.