Strain Adjustment in Si/Sige Superlattices

Abstract

ABSTRACTThe performance of future microelectronic circuits will be strongly enhanced by the monolithic integration of superlattice devices with convenventional integrated circuits ontop of a silicon substrate. With this material concept the mismatch between the superlattice materials and the silicon substrate has to be accommodated. SiGe/Si is a model system for the study of mismatch effects because of similar chemistry and well pronounced strain effects.Growth of SiGe/Si strained layer superlattices (SLS) by molecular beam epitaxy is reported. Adjustment of strain within the superlattice influences strongly the stability and band ordering of the SLS. SiGe/Si superlattices with strain symmetrization exhibit good thermodynamic stability and band ordering of type II. The concept of strain symmetrization by a thin homogeneous buffer layer is explained. Design rules for a virtual substrate consisting of the actual substrate with the thin buffer layer on it are given.