Non-homogeneity of In(x)Ga(1-x)N films is normally explained as spinodal decomposition. This origin does not seem reasonable since the spinodal decomposition descriptions did not take into account the coherency strain energy. As it was shown in [1] due to this energy spinodal decomposition of the wurtzite In(x)Ga(1-x)N is non-profitable in the total composition range at any temperature.

Non-homogeneity of the "conventional"epitaxial III-V alloys is two-dimensional in nature [2] and two-dimensional phase diagrams should describe it. The two-dimensional In(0.5)Ga(0.5)N phase diagram on the (0001)A surface is considered. This surface is the triangular cation lattice. The alloy is described as a regular solution with the interaction parameter between In and Ga equal to 22.7 kJ/mole for this lattice. Such solution is equivalent to the Ising model that has the exact solution (ES) in this case [3]. The strictly regular (SRA), quasichemical (QCA) and cluster variation (CVA) approximations are also applied. The temperatures of the miscibility gap and concentrations of In-Ga pairs at these temperatures, respectively, are given as at ES: T = 822 K, y = 0.1667; at CVA: T = 884 K, y = 0.25; at QCA: T = 1114 K, y = 0.4 and at SRA: T = 1348 K, y = 0.5. There is the great difference not only between the temperatures but between the concentrations as well. ES demonstrates that from the thermodynamics standpoint one-phase In(0.5)Ga(0.5)N is in the stable state and non-homogeneous at its growth temperatures. In fact, ES establishes an existence of the macroscopic phase separation at temperatures higher that the temperature of an occurrence of a miscibility gap.

References

2. T. L. McDevitt, S. Mahajan, D. E. Laughlin, W. A. Bonner, and V. G. Keramidis, Phys. Rev. B 45, 6614 (1992).

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1. Influence of the substrate orientation on the composition of solid solutions grown by LPE and MOCVD
2. Phase transitions in ZnTe doped with Mg and O