Critical Ge concentration for 2xn reconstruction appearing on GeSi covered Si(100)

Using reflection high-energy electron diffraction (RHEED), we monitored in situ the appearing of 2 x n reconstruction with different Ge compositions of GeSi alloys deposition, at growth temperature 600 degrees C. A relation between the thickness and Ge composition has been determined. To understand the relation, we perform a Ge segregation simulation 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 composition, such as Ge0.05Si0.95 alloy, there is no 2 x n reconstruction shown even when the deposited GeSi alloy film thickness exceeds its critical 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 rights reserved.