Localization and anticrossing of electron levels in GaAs1-xNx alloys

The electronic structure in nitrogen-poor GaAs1-xNx alloys is investigated using a plane-wave pseudopotential method and large supercells. Our calcula tions give a detailed description of the complex perturbation of the lowest conduction band states induced by nitrogen substitution in GaAs. The two p rincipal physical effects are (i) a resonant impurity state a(1)(N) above t he a(1)(Gamma(1c)) conduction band minimum (important at "impurity" concent rations, x similar to 10(17) cm(-3)) and (ii) the creation of a(1)(L-1c), a nd a(1)(X-1c) states due to the splitting of the degenerate L-1c and X-1c G aAs levels (important at alloy concentrations, x similar to 1% or similar t o 10(21) cm(-3)). We show how the interaction of a(1)(N), a(1)(Gamma(1c)), a(1)(L-1c), and a(1)(X-1c) provides a microscopic explanation for the origi n of the experimentally observed anomalous alloy phenomena. [S0163-1829(99) 50440-2].