First-principles calculations of gap bowing in InxGa1-xN and InxAl1-xN alloys:: Relation to structural and thermodynamic properties -: art. no. 075213

First-principles pseudopotential plane-wave calculations are used to investigate the electronic, structural, and thermodynamic properties of cubic nitride alloys InxGa1-xN and InxAl1-xN. The alloys are described within a cluster-expansion method considering configurations in large 64-atom supercells. We find a strong composition-dependent gap bowing for both InGaN and InAlN alloys. The strongest contribution to the gap bowing is due to a structural effect, i.e., the composition-induced disorder in the bond lengths. Charge transfer is found to be important only for InAlN alloys. A small deviation from Vegard's law is found for the lattice parameter variation in InGaN and InAlN alloys, The calculated first- and second-nearest-neighbor distances in InxGa1-xN alloys are in good agreement with the experimental data. The investigation of the thermodynamic stability of InGaN and InAlN alloys shows a significant tendency for spinodal decomposition.