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

Abstract

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, ΔEf <~ 0.004 eV/mole (mol = one cation + 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 X = 1/4, 1/2, and 3/4 (Pm, Pmn21 and Pm, respectively). In SiC-InN, one Cmc21 ordered phase is predicted at X = 1/2.