Electronic structure and optical properties of the quaternary alloy Ga1 − xAlxAsySb1 − y

A method for calculating the electronic structure of the quaternary alloy GaAlAsSb is presented. We have used the empirical pseudopotential method coupled with the virtual crystal approximation (VCA), which incorporates the compositional disorder as an effective potential. The electronic structures are studied for GaAlAsSb (x = 0.5, y = 0.6) and GaAlAsSb lattice matched to GaSb as well as InAs. In the case of GaSb lattice matched quaternary alloy, the bowing parameter for the Γ point gap is in good agreement with experimental results. In addition, a method for calculating the refractive indices at energies below the direct band edge is presented. The photon energies dependence of the refractive index is calculated with the model of dielectric constants of semiconductors based on simplified models of the interband transitions. Also the composition dependence of the refractive index is discussed, the result indicates that the refractive index increases with alloying for the quaternary alloy GaAlAsSb lattice matched to GaSb.