Optical transitions in dilute GaNxAs1-xGaNxAs1-x nitrides: A comparison between ab initio and empirical pseudopotentials

Ab initio   Troullier–Martins and empirically adjusted Hartwigsen–Goedecker–Hutter pseudopotentials have been used, within the density-functional theory (DFT) framework, to study the optical transitions in the dilute nitride, GaNxAs1-xGaNxAs1-x. Composition dependence of the energy gap (E-E-) and the E+E+ optical transitions have been computed with the two pseudopotentials. Band anticrossing (BAC) model parameters have been derived from the composition dependence of the DFT E-E- and E+E+ optical transitions, providing DFT-based analytical expressions for E+(x)E+(x) and E-(x)E-(x). The influence of the N configuration (ordered or randomly distributed in the GaAs host material) has been studied. Random distribution is found to increase the energy gap E-E-, compared to ordered structures, but has relatively little effect on the E+E+ energy. Comparisons with the experimental and tight-binding data are reported.