ELECTRONIC-STRUCTURE AND OPTICAL-PROPERTIES OF THE QUATERNARY ALLOY GA1-XALXASYSB1-Y

A method for calculating the electronic structure of the quaternary al loy GaAlAsSb is presented. We have used the empirical pseudopotential method coupled with the virtual crystal approximation (VCA). which inc orporates the compositional disorder as an effective potential. The el ectronic structures are studied for GaAlAsSb (x = 0.5, y = 0.6) and Ga AlAsSb lattice matched tu GaSb as well as InAs. In the case of GaSb la ttice matched quaternary alloy, the bowing parameter for the Gamma poi nt gap is in good agreement with experimental results. In addition, a method for calculating the refractive indices at energies below the di rect band edge is presented. The photon energies dependence of the ref ractive index is calculated with the model of diielectric constants of semiconductors based on simplified models of the interband transition s. Also the composition dependence of the refractive index is discusse d, the result indicates that the refractive index increases with alloy ing for the quaternary alloy GaAlAsSb lattice matched to GaSb.