Origin of the band-edge states in [001] thin superlattices of GaAs/AlAs

Abstract

The self-consistent pseudopotential method is used to investigate the origin of the valence- and conduction-band edge states in thin [001] superlattices of (GaAs)n-(AlAs)n, for n=2, 3, and 4. We find that these superlattices have a staggered band alignment (type II superlattice), with the highest occupied valence-band state (hole) localized in the GaAs region and the lowest unoccupied conduction-band state (electron) localized in the AlAs region. The change in the lowest conduction-band edge states in the GaAs and AlAs region with layer thickness, suggests a transition to a nonstaggered alignment (type I superlattice) at large layer thicknesses. A critical layer thickness is estimated for this transition.