Splitting of the states derived from the bulk X minima in GaAs-AlAs superlattices

Abstract

We have carried out full-scale pseudopotential calculations on (GaAs)n-(AlAs)n superlattices (n>2) to determine the relative alignment of the superlattice conduction states derived from the secondary bulk X minima. These are states characterized by contributions from the bulk minima oriented along the growth axis 001 (Xz) and states characterized by the bulk (010) (Xy) and (100) (Xx) minima that lie in the plane of the interfaces. We present the splitting in energy of Xz and Xx,Xy levels for 2<n<15 and report that the lowest superlattice state is related to Xz. We discuss the origin of this splitting, determine the oscillator strengths of optical transitions to the valence band, and compare with experimental data. We argue that the position of the Xx,Xy levels may be used to assess the quality of the interface at the microscopic level. © 1989 The American Physical Society.