Localization and anticrossing of electron levels inGaAs1−xNxalloys

The electronic structure in nitrogen-poor ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ 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 $a_1\mathrm{}\left(N\right)\mathrm{}$ above the $a_1\left({\Gamma }_{1c}\right)$ conduction band minimum (important at “impurity” concentrations, $x\sim {10}^{17}\hspace{0.5em}{\mathrm{cm}}^{-3})$ 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, $x\sim 1\%$ or $\sim {10}^{21}\hspace{0.5em}{\mathrm{cm}}^{-3}).\mathrm{}$ We show how the interaction of $a_1\mathrm{}\left(N\right),$ $a_1\left({\Gamma }_{1c}\right),$ $a_1{(L}_{1c}),$ and $a_1{(X}_{1c})$ provides a microscopic explanation for the origin of the experimentally observed anomalous alloy phenomena.