Electronegativity effects on the bandgap bowing characters in compound-semiconductor ternary alloys

We present a theoretical investigation of the existence and origins of the bandgap bowing character in compound semiconductor alloys based on both the sp³s*-tight-binding (TB) method, which includes the spinorbit coupling, and the first-principle Full-Potential Linear Augmented Plane Wave (FP-LAPW) technique. First, we compare the bandgap variation versus composition in the III-V direct-bandgap-GaAs-based ternary alloys, namely between the common-cation GaSb_xAs_1-x and the common-anion Ga _1-xIn_xAs ternary alloys. The results show that the bowing behavior exists only in the common-cation (i.e., GaSbAs) alloys as a result of an existing competition between the anion atoms (Sb and As) in trapping the electronic charge. The bowing parameter is found to be proportional to the electronegativity characters of the competing anions (i.e., χ ^anion). The lack of such competition, in the case of common-anion alloys (i.e., GaInAs), makes the bowing be just absent and the variation of the bandgap become close to linear. Second, we have made a clear contrast in the bowing characters between the common-cation III-V and the common-anion II-V ternary alloys by assessing the effect of anion electronegativity (as example, we consider the GaSb_xAs_1-x and CdSe_xTe _1-x ternary alloys). The results show that the bowing character in the II-VI alloys is stronger than the one of III-V alloys as to be simultaneously proportional to the electronegativity of anions (χ^anion_ave) and to the electronegativity mismatch between them (Δχ ^anion/χ^anion _ave). Finally, the excellent agreement between our theoretical results and recent photoluminescence data has further corroborated our claims.