First principles phase diagram calculations for the wurtzite-structure systems AlN-GaN, GaN-InN, and AlN-InN

First principles phase diagram calculations were performed for the wurtzite-structure quasibinary systems AlN-GaN, GaN-InN, and AlN-InN. Cluster expansion Hamiltonians that excluded, and included, excess vibrational contributions to the free energy, F-vib, were evaluated. Miscibility gaps are predicted for all three quasibinaries, with consolute points, (X-C,T-C), for AlN-GaN, GaN-InN, and AlN-InN equal to (0.50, 305 K), (0.50, 1850 K), and (0.50, 2830 K) without F-vib, and (0.40, 247 K), (0.50, 1620 K), and (0.50, 2600 K) with F-vib, respectively. In spite of the very different ionic radii of Al, Ga, and In, the GaN-InN and AlN-GaN diagrams are predicted to be approximately symmetric. (c) 2006 American Institute of Physics.