Electronic density of states of semiconductor alloys from lattice-mismatched isovalent binary constituents

Abstract

We present a model of the electronic density of states (DOS) for a wide class of ternary and quaternary semiconductor alloys. Our approach is based on a large-cluster calculation using a semiempirical tight-binding model for the electronic structure. The microscopic lattice configuration is efficiently determined by a Keating potential for the strain energy. The electronic DOS is calculated numerically via the recursion method. Results are presented for ${\mathrm{ZnSe}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Te}}_{\mathit{x}}$. It is shown that the strong band bowing observed for this material is due to pure compositional disorder and bond-angle fluctuations. Bond-length fluctuations are found to be of minor significance. Without any free, adjustable parameters for the alloy, our model is in quantitative agreement with experimental data on the composition dependence of the main energy gap.