Deep levels in strained Si/Ge superlattices

Abstract

The deep levels associated with vacancies and substitutional impurity atoms in (Si) n/(Ge) m strained-layer superlattices (SLSLs) grown on Si 1-xGe x substrates are investigated theoretically. The band structures of the SLSLs are calculated using the empirical tight-binding method. The atomic geometries of the SLSLs are determined by valence-force-field calculations. The defect levels are computed using the Green's function method. We find that the energies of defect levels are influenced largely by the strains, the positions of the impurity atoms, and the thicknesses n and m of the Si and Ge layers. The splittings of the three-fold degenerate p-like defect levels are especially large at interface sites. Under certain conditions, some deep levels that lie in the band gap for bulk hosts may become resonant in SLSLs.