To acquire high mobilty device and control the bandgap, it is needed that $Si_{1-x}Ge_x$ thin film should be grown with Ge composition control, which can be realized using Molecular Beam Epitaxy. But there is a lattice mismatch between Si substrate and $Si_{1-x}Ge_x$ thin film, so the thicker the film thickness or higher the Ge composition, the more the mifit dislocation and strain relaxation are derived.
Before growing $Si_{1-x}Ge_x$ thin film which will be used as high mobilty device, we must grow buffer layer film which prevent defects from transferring upper device. So, surface morphology of buffer layer must be clean. The strain relaxation is controlled by growth temperature and heat treatment temperature and substrate bias when Ge composition and film thickness are fixed. Although the buffer layer is widely used there had been few work related quantitative study of strain relaxation as temperature and bias are varied.
The aim of this work is to investigate the effect of growth temperature and heat treatment temperature and substrate bias on strain relaxation in the critical thickness. And this work can give good information of acquiring a good quality buffer layer.
