Bandgap characters in GaAs-based ternary alloys

The existence and origins of the bowing character in the bandgap variation of GaAs-based ternary alloys are theoretically investigated based on two different computational methods. Within the framework of the virtual crystal approximation (VCA), both the empirical sp³s* tight-binding (TB) method with, and without, the inclusion of the spin-orbit coupling effects, and the first-principle full-potential linear augmented plane wave (FP-LAPW) technique are applied on both the common-cation GaSb_xAs_1-x and the common-anion Ga_1-xm_xAs alloys. These methods are used to calculate the bandgap energy, the partial and total densities of states and the constituent charge ionicity versus the composition x. The results show that the bowing behavior exists in the case of common-cation alloys (GaSb _xAs_1-x) as a manifestation of a competition between the anion atoms (As and Sb) in trapping the made-available-cationic charges. The bowing parameter is found to be proportional to the electronegativity characters of the competing anions ((anion). Consistent with this in the case of common-anion alloys (Ga_1-xIn_xAs), as due to the lack of anion competition, the bowing is just absent and the variation of bandgap energy is found to be rather linear. The excellent agreement between our theoretical results and recent photoluminescence data has corroborated our claim.