Ž .Applied Surface Science 162–163 2000 425–429www.elsevier.nlrlocaterapsusc

Growth and optimization of InAsrGaSb and GaSbrInAsinterfaces

A. Tahraoui b, P. Tomasini a, L. Lassabatere a, J. Bonnet a,)`a ( )Laboratoire d’Analyse des Interfaces et de Nanophysique LAIN UPRESA CNRS 5011, UM II-STL, cc 082, Place E. Bataillon,

34095 Montpellier Cedex 5, Franceb Center for Quantum deÕices, ECE Department, Northwestern UniÕersity, 2145 Sheridan Road, EÕanston, IL 60208, USA

Abstract

In order to optimize the molecular beam epitaxy growth of indium arsenide–gallium antimonide structures, we study theeffects of the stacking sequence of the interfacial monolayer and of the growth temperature. To this end, GaSbrInAs andInAsrGaSb heterojunctions involving ultra-thin epilayers have been fabricated at 3508C, 4008C and 4508C with In–Sb- orGa–As-like interfaces. The structures have been investigated by reflection high-energy electron diffraction, Auger electron

Ž . Ž .microscopy and atomic force microscopy. The best growth condition for InAs 100 as well as GaSb 100 have been obtainedwith a substrate temperature of 4008C and an In–Sb-like InAs–GaSb interface. q 2000 Elsevier Science B.V. All rightsreserved.

PACS: 81.05.Ea; 81.15.HiKeywords: InAs; GaSb; MBE; Epitaxy; Interface; Semiconductor

1. Introduction

Indium arsenide and gallium antimonide arepromising candidates for a variety of device applica-tions including infrared detectors, mid-wave infrared

w xlasers and high-speed electronics 1 . Despite of asignificant progress in device fabrication, the perfor-mances are still below one might expect. Since adevice performance is a function of the structuralquality of the heterojunctions, our contribution to the

Ž .E-mail addresses: tahraoui@ece.nwu.edu A. Tahraoui ,Ž .bonnet@lain.univ-montp2.fr J. Bonnet .

) Corresponding author. Tel.: q33-46-714-3200; fax: q33-46-714-3774.

device improvement focuses on the optimization ofthe GaSb–InAs interface. In this paper, we investi-gate the effects of the nature of the interfacial mono-

Ž .layer In–Sb- or Ga–As-like and of the growthtemperature on the quality of interface heterostruc-tures.

2. Experiments

The samples were grown by solid-source molecu-Ž .lar beam epitaxy MBE as described previously

w x2,3 . The GaSb and InAs substrates were n-typeŽ .100 . The epilayers were grown at 3508C, 4008C

w xand 4508C on a buffer layer 4,5 . The interfacebonds, i.e. In–Sb-like or Ga–As-like were controlled

0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0169-4332 00 00227-0

( )A. Tahraoui et al.rApplied Surface Science 162–163 2000 425–429426

Ž .by migration enhanced epitaxy MEE . The layer-by-layer growth mode was controlled by reflection

Ž .high-energy electron diffraction RHEED . The InAsand GaSb growth rates were 0.3 molecular mono-

Ž .layer per second MLrs and 0.5 MLrs, respec-tively. The epilayer thicknesses are typically 1.5 nm.The room temperature Auger electron spectroscopyŽ .AES analysis involved the Ga1070, In404, As1228

w xand Sb454 peaks 1,6 . Atomic force microscopyŽ .AFM images were scanned at atmospheric pressurein a contact mode.

3. Results

Ž .The deposition of 1 ML of In on a c 2=6Ž . Ž .GaSb 100 surface leads to a 1=3 pattern, while a

Ž .2=3 pattern is seen with 1 ML of Ga. However,Ž .the RHEED pattern changes to a 2=4 when open-

ing the As shutter.4

AES results are summarized in Table 1. TheAsrIn peak ratio ranges from 2.82 to 3.61 dependingon the growth conditions. Our reference is the peakratio of thick InAs epilayers grown by MBE that is

w xfound typically close to 3 1 .AFM views of InAs surfaces are given by Fig.

Ž . Ž . Ž . Ž .1 1 to 6 . The samples 1 to 3 show wavysurfaces with a large density of islands and pitches,

Ž . Ž .while Fig. 1 4 to 6 shows smooth surfaces. Espe-cially, the InAs epilayers grown at 4008C with anIn–Sb-like interface show atomically stepped sur-

Ž . Žfaces with a root mean square RMS of 0.3 nm ;1. Ž Ž ..ML see Fig. 1 5 .

The deposition of 1 ML of In or Ga on anŽ . Ž .InAs 100 surface leads to a 4=2 pattern. The

Ž .RHEED pattern changes to a c 2=6 reconstructionwhen growing GaSb.

Table 1 gives the AES SbrGa peak ratio of theGaSb epilayer surfaces. The values span from 0.81to 0.99, while the peak ratio for a GaSb buffer is

w xtypically 1 1 .Ž . Ž .The AFM pictures 7 to 12 show typical GaSb

epilayers surfaces. The samples grown at 4008Cexhibit the best RMS, typically 0.3 nm for the

Ž . Ž .sample 11 and 0.6 nm for the sample 8 .

4. Discussion

The epilayer composition is expected to be closerto the binary composition as the AES peak ratio ofthe epilayers is closer to the bulk one. The AESinvestigation shows that the best InAs epilayers arefabricated at 4008C. It seems at this point that theinterface bonds does not matter too much since thetwo types of interfaces lead to similar AES resultsŽ .see Table 1 . The AFM observations allows us toselect the In–Sb-like interface as definitively leadingto the best InAs epilayers, and therefore, the best

Ž Ž ..InAsrGaSb interface see Fig. 1 5 . A similar anal-ysis applied to the GaSb epilayers observation leadsto a similar conclusion.

The growth optimum for the epitaxy of InAs onGaSb is similar to the one of GaSb on InAs. How-ever, we observe that the flatness of the two epilay-ers is not exactly comparable: molecular steps aremore clearly visible for InAs than GaSb despite

Ž Ž . Ž ..similar RMS values see Fig. 1 5 and 11 . Thefilm topology might be a consequence of the largermobility of the In adatoms comparatively to the Gaones.

Table 1AES measurements of several samples grown at different temperatures with controled interfaces

Ž .Temperature 8C Interface type InAsrGaSb GaSbrInAs

AsrIn ratio RHEED pattern GarSb ratio RHEED pattern

Ž . Ž .350 In–Sb 2.82 sharp 2=4 0.81 sharp c 2=6Ž . Ž .Ga–As 3.56 weak 2=4 0.87 weak c 2=6Ž . Ž .400 In–Sb 2.90 sharp 2=4 0.98 sharp c 2=6Ž . Ž .Ga–As 3.11 weak 2=4 0.96 weak c 2=6Ž . Ž .450 In–Sb 3.61 sharp 2=4 0.91 sharp c 2=6Ž . Ž .Ga–As 3.31 weak 2=4 0.92 weak c 2=6

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Ž . Ž . Ž . Ž .Fig. 1. AFM top view of ultra-thin pseudomorphic epilayers grown at 3508C, 4008C and 4508C, respectively, 1 to 3 InAs with a Ga–As-like interface, 4 to 6 InAs with anŽ . Ž . Ž . Ž .In–Sb-like interface; 7 to 9 GaSb with a Ga–As-like interface, 10 to 12 GaSb with an In–Sb-like interface.

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In addition, this work gives evidence that theGaSb and InAs growth do not depend exactly onsimilar parameters. The AES results show that theInAs stoichiometry depends on the growth tempera-ture and the interface type, while the GaSb onedepends mainly on the growth temperature. How-ever, the AFM results allow a fine-tuning of theanalysis: the pictures of samples with a Ga–As-likeinterface show clearly poorer surfaces and this analy-

Žsis is consistent with the RHEED observations see.Table 1 .

5. Conclusion

To the end to improve experimental device fabri-cation, this study focused on the InAsrGaSb andGaSbrInAs interface growth. The influence of thesubstrate temperature and interface bond type on theepilayers roughness and composition has been inves-tigated by RHEED, AES and AFM. Our results showthat the interface bond play a key role for the growthof high-quality InAs epilayers on GaSb, while theleading parameter for the growth of GaSb epilayerson InAs is the growth temperature. The best InAsand GaSb epilayers are grown with an In–Sb inter-

face at 4008C. An InAsrGaSb heterojunction with aMEE controlled In–Sb-like interface monolayergrown at 4008C allows a layer by layer growthmode. Therefore, an atomically abrupt interface thatshould lead to a device improvement is expected.

Acknowledgements

A. Tahraoui is deeply indebted to Pr. G. Levequefor many valuable discussions on AFM measure-ments and to J. Touret for technical assistance on theMBE machine.

References

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