Energy gaps and refractive index of lattice-matched and mismatched InxAl1−xAsySb1−y quaternaries

The electronic band structure and optical properties of InxAl1-xAsySb1-y quaternaries under conditions of lattice mismatching and lattice matching to InP substrate have been investigated using a pseudopotential approach under the virtual crystal approximation. The extent of the indirect (Г-X)-to-direct (Г-Г) band gap transition in InxAl1-xAsySb1-y/InP is found to occur at x = 0.38 which agrees reasonably with the data reported in the literature. The lattice mismatch percentage in the range −5%-0% is found to have no effect on the nature of the fundamental band-gap in In0.50Al0.50AsySb1−y which remains a direct (Г-Г) band-gap semiconductor. Trends in bonding and ionicity are discussed in terms of the antisymmetric gap and valence band width. The dependence of the refractive index on both indium concentration x in InxAl1−xAsySb1−y/InP and lattice mismatch percentage in In0.50Al0.50AsySb1-y has been examined. Our results showed that more opportunities can be provided for all features of interest by a proper choice of the concentrations x and y (0 ≤ x ≤ 0.52, 0.56 ≤ y ≤ 1) and/or the lattice mismatch percentage.