Theoretical study of phase separation in wurtzite InGaN

Phase separation in wurtzite InxGa1−x  N is investigated theoretically by ab initio calculations. The calculated mixing free energies are positive with a maximum at composition x=0.4375x=0.4375 and the spinodal decomposition will occur while the lattice is in equilibrium and uniformity. The mixing free energies turn into negative and have three retuse minima at compositions of 0.3125, 0.5000, and 0.6875 if strain is introduced by replacing the GaN or InN lattice constant with the equilibrium lattice constants. Detailed comparisons among the clustered, phase-separated, and uniform atomic configurations show that InN cluster is favourable in energy if the lattice is further fully relaxed, but uniform distribution is kept on under the strained lattices. The results indicate that the phase separation can be suppressed under either the compressive or tensile stress field.