Theoretical analysis of disorder effects on electronic and optical properties of the quaternary alloy In_1–xGa_xAs_ySb_1–y epilayer on GaSb and InAs

Abstract

The effects of structural and chemical disorder on electronic and optical properties of In_1–xGa_xAs_ySb_1–y quaternary alloy are studied on the basis of a modified virtual crystal approximation calculated within a simple tight-binding sp³s* theory, which incorporates relaxation parameters and compositional disorder as an effective potential. Using a minimal set of fitting parameters, we show that such an approach provides analytical results for calculating energy gaps and bowing parameters. The electronic structure are studied for In_1–xGa_xAs_ySb_1–y (x = 0.5, y = 0.5) and In_1–xGa_xAs_ySb_1–y lattice matched to GaSb and as well as to InAs. In addition, a method for calculating the refractive indices at energies below the direct band gap edge is presented. The photon energy 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 an In_1–xGa_xAs_ySb_1–y lattice matched to InAs and GaSb. The lattice thermal resistivity has been calculated using interpolation schemes. The result indicates that the thermal resistivity of an In_1–xGa_xAs_ySb_1–y lattice matched to InAs and GaSb for the composition of (0 ≤ x ≤ 1) increases markedly with alloying and exhibits a maximum value of about 41 W^–1 deg cm at an alloying composition of x ≅ 0.45 and about 40 W^–1 deg cm at an alloying composition of x ≅ 0.50 for InGaAsSb on a substrate of GaSb and InAs, respectively.