Using reflection high-energy electron diffraction (RHEED), we monitore
d in situ the appearing of 2 x n reconstruction with different Ge comp
ositions of GeSi alloys deposition, at growth temperature 600 degrees
C. A relation between the thickness and Ge composition has been determ
ined. To understand the relation, we perform a Ge segregation simulati
on using the two-stale exchange kinetic model. As the Ge concentration
in the top layer reaches about 0.8 for all Ge compositions. due to Ge
segregation, the 2 x n reconstruction begins to appear to release the
accumulated misfit strain. For a GeSi alloy with very low Ge composit
ion, such as Ge0.05Si0.95 alloy, there is no 2 x n reconstruction show
n even when the deposited GeSi alloy film thickness exceeds its critic
al thickness, because the saturated Ge concentration of the top layer
in such alloys is lower than 0.8. (C) 1998 Elsevier Science B.V. All r
ights reserved.