New Ordering-Induced Optical Transitions in Strained Sige Superlattices

Abstract

ABSTRACTFirst principles total energy and electronic structure calculations for SinGen superlattices grown epitaxially on a Si (001) substrate reveal a nearly direct band gap despite the pronounced indirectness of the Si0.5Ge0.5alloy. While the new direct superlattice transitions have their origin in folded indirect transitions of the random alloy, their transition matrix elements are considerably enhanced by superlattice atomic relaxation and the superlattice ordering potential. For a superlattice grown on a substrate with an lager lattice contant than we predict a nearly direct band gap.