Structure and phase stability of ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P solid solutions from computational alchemy

The structural and thermodynamical properties of ${\mathrm{Ga}}_{\mathit{x}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P solid solutions are studied using Monte Carlo simulations based on density-functional perturbation theory. The free-standing alloy displays a model random behavior, with a miscibility gap below ∼820 K. In samples grown on a GaAs (001) substrate, the resulting epitaxial strain stabilizes various ordered phases which give rise to a rich phase diagram below ∼230 K. Among these phases, the chalcopyrite is dominant for x=0.5, and two new, more complex, stable phases have been identified at different concentrations.