Electronic Structure of Intentionally Disordered AlAs/GaAs Superlattices

Abstract

We use realistic pseudopotentials and a plane-wave basis to study the electronic structure of nonperiodic, three-dimensional, 2000-atom (AlAs${)}_{\mathit{n}}$/(GaAs${)}_{\mathit{m}}$ (001) superlattices, where the individual layer thicknesses $n,m\ensuremath{\in}{1,2,3}$ are randomly selected. We find that while the band gap of the equivalent ( $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$) ordered superlattice is indirect, random fluctuations in layer thicknesses lead to a direct gap in the planar Brillouin zone, strong wave function localization along the growth direction, short radiative lifetimes, and a significant band-gap reduction, in agreement with experiments on such intentionally grown disordered superlattices.