Electronic structure of intentionally disordered AlAs/GaAs superlattices.

We use realistic pseudopotentials and a plane-wave basis to study the electronic structure of nonperiodic, three-dimensional, 2000-atom (AlAs){sub {ital n}}/(GaAs){sub {ital m}} (001) superlattices, where the individual layer thicknesses {ital n},{ital m}{element_of}{l_brace}1,2,3{r_brace} are randomly selected. We find that while the band gap of the equivalent ({ital n}={ital m}=2) {ital ordered} superlattice is indirect, random fluctuations in layer thicknesses lead to a {ital 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.