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

Abstract

Using reflection high-energy electron diffraction (RHEED), we monitored in situ the appearing of 2× n reconstruction with different Ge compositions of GeSi alloys deposition, at growth temperature 600°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-state 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× n reconstruction begins to appear to release the accumulated misfit strain. For a GeSi alloy with very low Ge composition, such as Ge 0.05Si 0.95 alloy, there is no 2× 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.