Optical and structural studies of relaxation in SI_1-xGE_x SI strained-layer superlattices

Asymmetrically and symmetrically strained Si SiGe superlattices were grown on Si(001) by Molecular Beam Epitaxy (MBE) and studied as a function of thermal treatments. X-ray diffraction was used to monitor the extent of interdiffusion with annealing time and temperature and results indicate that initially the interdiffusion is very rapid and non-linear, but later a steady-state regime is attained. Raman spectroscopy has shown that in the very early heating stages, strain relaxation occurs predominantly by interdiffusion, and Ge diffusion can be enhanced by strain. The results also indicate that a significant contribution to the interdiffusion occurs by an interstitial-type mechanism.