Electronic structure and phase stability ofGaAs1−xNxalloys

Using first-principle total-energy calculations we investigated the electronic structure and stability for several compositions and for various ordered structures of ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{N}}_{\mathit{x}}$ alloys. Our results show a strong bowing of the band gap which is consistent with recent experimental observations. For certain compositions the alloy may even become metallic; a process which is mainly driven by a strong atomic relaxation. Based on the calculated formation energies and assuming thermodynamic equilibrium a strong miscibility gap between these two structures is found. This is explained in terms of the large mismatch in the lattice constants between GaAs and GaN (more than 20%).