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 [1]. Precise control of Sb vapor pressure during TC process is very important in order not to form either Sb hillocks or rough surfaces [1].

    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 [2]. 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.

Reference

[1] R. M. Biefeld., Mat. Sci. Eng., R 36, 105 (2002)

[2] M. C. Lavine, A. J. Rosenberg and H. C. Gatos., J. Appl. Phys., 29, 1131 (1958)

[3] R. L. Schwoebel., J. Appl. Phys., 40, 614 (1969): R. L. Schwoebel and E. J. Shipsey., J. Appl. Phys., 37, 3682 (1966)

1. PRESENTATION: Effects of TMSb overpressure on InSb surface morphologies during a thermal cleaning process by metal organic chemical vapor deposition, Microsoft Office Document, 0.1MB

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