Optical second harmonic generation studies of epitaxial growth of Si and SiGe

Optical second harmonic generation (SHG) from Si surfaces has the advantage of surface sensitivity and can be applied in-situ during epitaxial growth process such as gas source molecular beam epitaxy (GSMBE) or chemical vapou r depositions (CVD). This enables a number of processes occurring on the su rface during epitaxial growth to be investigated in real time. Two processe s are of particular interest in the epitxial growth of Si and SiGe structur es: (1) oscillatory processes on the surface due to layer-by-layer growth f or growth rate measurements and (2) surface segregation of Ge during format ion of Si/SiGe heterojunctions. In this paper, we report on the oscillatory SHG response from the Si(0 0 1) surface during homo-epitaxy of Si and vari ations of SHG response across the SiGe/Si heterojunction during GSMBE growt h, The oscillatory response is attributed to the domain coverage variation during layer-by-layer growth analogous to the origin of reflectance anisotr opy oscillations. The changes in SHG during formation of SiGe/Si heterojunc tion is attributed to the gradual variation of surface Ge concentration due to segregation of Ge. The contribution from buried interfaces is shown to be negligible at the photon energy used. (C) 2000 Elsevier Science B.V. All rights reserved.