Effects of atomic short-range order on the electronic and optical properties of GaAsN, GaInN, and GaInAs alloys

Using large (≈500--1000atoms) pseudopotential supercell calculations, we have investigated the effects of atomic short-range order (SRO) on the electronic and optical properties of dilute and concentrated GaAsN, GaInN, and GaInAs alloys. We find that in concentrated alloys the clustering of like atoms in the first neighbor fcc shell (e.g., N-N in GaAsN alloys) leads to a large decrease of both the band-gap and the valence-to-conduction dipole transition-matrix element in GaAsN and in GaInN. On the other hand, the optical properties of GaInAs depend only weakly on the atomic SRO. The reason that the nitride alloys are affected strongly by SRO while GaInAs is affected to a much lesser extent is that in the former case there are band-edge wave-function localizations around specific atoms in the concentrated random alloys. The property for such localization is already evident at the (dilute) isolated impurity and impurity-pair limits.