Defects in SiGe virtual substrates for high mobility electron gas

We have investigated the morphology defects, in particular, pits present in compositionally graded SiGe thick films heteroepitaxially grown on Si(001) surfaces. Besides the pits clearly related to impurities and interface defects, a class of pits intrinsic to the strained-layer growth has been found. Two stable and one metastable pit shapes have been identified that can be related to the alloy film thickness and pit dimension. The influence of the pits on the mobility of the two dimensional electron gas grown on these kinds of substrates has been also investigated.