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 calculations give a detailed description of the complex perturbation of the lowest conduction band states induced by nitrogen substitution in GaAs. The two principal physical effects are (i) a resonant impurity state a(1)(N) above the a(1)(Gamma(1c)) conduction band minimum (important at "impurity" concentrations, x similar to 10(17) cm(-3)) and (ii) the creation of a(1)(L-1c), and a(1)(X-1c) states due to the splitting of the degenerate L-1c and X-1c GaAs levels (important at alloy concentrations, x similar to 1% or similar to 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 origin of the experimentally observed anomalous alloy phenomena. [S0163-1829(99)50440-2].