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

The cluster-expansion method was used to perform first principles phase diagram calculations for the wurtzite-structure quasibinary systems (SiC)1 X(AlN)X, (SiC)1 X (GaN)X and (SiC)1 X(InN)X; and to model variations of band gaps as functions of bulk compositions and temperature. In SiC-AlN, plane wave pseudopotential formation-energy calculations predict low-energy metastable states with formation energies, DEf . 0.004 eV/mole (mol1⁄4 one cationþ one anion). The crystal structures of these states are all of the form (SiC)m(AlN)n(SiC)o(AlN)p ... (m,n,o,p integers), where (SiC)m indicates m SiC-diatomic-layers ? to the hexagonal c-axis (cHex) and similarly for (AlN)n, (SiC)o and (AlN)p. The presence of low-energy layer-structure metastable states helps to explain why one can synthesize (SiC)1 X(AlN)X films, or single crystals with any value of X, in spite of the apparently strong tendency toward immiscibility. In SiC-GaN, ordered structures are predicted at X1⁄4 1/4, 1/2, and 3/4 (Pm, Pmn21 and Pm, respectively). In SiC-InN, one Cmc21 ordered phase is predicted at X1⁄4 1/2. VC 2011 American Institute of Physics. [doi:10.1063/1.3602149]