Nitrogen-electronegativity-induced bowing character in ternary zincblende Ga_1-xIn_xN alloys

The origins of the bandgap bowing character in the common-anion ternary cubic Ga_1-xIn_xN alloys are investigated using the sp ³s^* tight-binding (TB) method, including the spin-orbit coupling effects within the virtual-crystal approximation (VCA) framework. The method is used to calculate the band structure, density of states and charge ionization versus composition and valence-band offsets (VBO). The results are used to model some recently available experimental optical absorption (Abs) and photoluminescence (PL) data. Two unusual characteristics are discussed: (i) unlike the common-anion "direct-bandgap- based" ternary alloys, the GaInN alloys possess a clearly large bowing character. This behavior is found to be mainly caused by the electronegativity of nitrogen atoms, whose effects can induce a competition between the cation (Ga and In) atoms to establish a compromised ionization with the increasing indium content; (ii) a single composition-independent bowing parameter cannot describe the bandgap behavior. The decrease of bowing parameter with the increasing In content is found to be almost linear and likely to be caused by the composition fluctuation due to the large lattice relaxation. The results also show that the VBO between the two constituents is small (VBO < 0.38 eV), consistent with the predictions of the common-anion rule and the state-of-the-art ab initio methods.