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Effects of TMSb overpressure on InSb surface morphologies during a thermal cleaning process by metal organic chemical vapor deposition
|Sehun Park 1,2, Jinwook Jung 1,2, Sung Hyun Park 1, Chulkyun Seok 1, Keun Wook Shin 1, Yasushi Nanishi 2,3, Euijoon Yoon 1,2,4|
1. Seoul National University (SNU), School of Mat. Sci. Eng., Seoul 151742, Korea, South
In preparation for a high quality epitaxial layer of InSb by metal organic chemical vapor deposition (MOCVD), a substrate cleaning step such as in-situ thermal cleaning (TC), prior to the epitaxial growth, is an important process. This is a crucial step for preparing chemically clean, atomically flat and oxide-free surfaces. In contrary to the TC of III-V arsenic and phosphorus based compound semiconductors such as GaAs and InP etc, TC under Sb overpressure causes a controversial problem due to the low equilibrium vapor pressure of Sb during the growth of Sb-based compound semiconductors . Precise control of Sb vapor pressure during TC process is very important in order not to form either Sb hillocks or rough surfaces .
In this study, InSb substrates were thermally cleaned in either H2 or TMSb ambient to understand how the surface of InSb was affected by TC ambient. From the scanning electron microscope image as shown in Fig. 1-(a), we observed In droplets on the InSb surfaces when thermally treated at 515 oC in H2 ambient. In droplets were generally formed by In oxides decomposition as well as InSb decomposition. The large In droplets with a diameter of about 2.5 μm were found within the rectangular etch pits on the surfaces. It was bounded with <111> sides. The facets in the etch pits were originated from the relative reactivity differences of various crystallographic planes of InSb . Atomic force microscope was used to analyze surface morphology of InSb substrates thermally cleaned at 515 oC under TMSb overpressure. At a TMSb flow rate of 18.1 μmol/min, multi-layered mounds were formed on the InSb substrates as shown in Fig. 1-(b). This was caused by initial substrate morphologies, low Sb lateral diffusion length and Schwoebel potential barrier at the step edges [3, 4]. With increased TMSb flow rate of 126.7 μmol/min, the multi-layered mounds were evolved to a step-flow surface through the coalescence of mounds, as represented in Fig. 1-(c). The same surface evolution was also observed as TC time increases. The variation of TC temperature from 475 to 515 oC did not, however, affect the surface evolution of InSb substrate. The detailed experiment results and discussions about the effects of TMSb overpressure on InSb surfaces morphologies will be addressed.
Fig. 1 InSb surface thermally treated under difference ambient conditions during thermal cleaning process: (a) H2 ambient, (b) TMSb ambient at a flow rate of 18.1 μmol/min, and (c) TMSb ambient at a flow rate of 126. 7 μmol/min.
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Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 9, by Sehun Park
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-04-14 16:02 Revised: 2013-04-14 16:41