First-principles calculations of the thermodynamic and structural properties of strained ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ and ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloys

We present first-principles calculations of the thermodynamic and structural properties of cubic ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ and ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloys. They are based on the generalized quasichemical approach to disorder and composition effects and a pseudopotential-plane-wave approximation for the total energy. The cluster treatment is generalized to study the influence of biaxial strain. We find a remarkable suppression of phase separation in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}.$