Disorder effects on the density of states of the II-VI semiconductor alloys ${\mathrm{Hg}}_{0.5}$${\mathrm{Cd}}_{0.5}$Te, ${\mathrm{Cd}}_{0.5}$${\mathrm{Zn}}_{0.5}$Te, and ${\mathrm{Hg}}_{0.5}$${\mathrm{Zn}}_{0.5}$Te

The electronic structure of substitutionally random ${\mathit{A}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{B}}_{\mathit{x}}$C alloys of zinc-blende semiconductors AC and BC departs from what a virtual-crystal approximation would grant both because of (i) a chemical perturbation, associated with an electronicmismatch between atoms A and B, and because of (ii) a structural perturbation (positional relaxation) induced by a size mismatch between A and B. Both effects on the electronic density of states are studied here for ${\mathrm{Hg}}_{0.5}$ ${\mathrm{Cd}}_{0.5}$Te, ${\mathrm{Cd}}_{0.5}$ ${\mathrm{Zn}}_{0.5}$Te, and ${\mathrm{Hg}}_{0.5}$ ${\mathrm{Zn}}_{0.5}$Te in the context of first-principles self-consistent supercell models. We use our recently developed ‘‘special quasirandom structures’’ [A. Zunger, S.-H. Wei, L. G. Ferreira, and J. E. Bernard, Phys. Rev. Lett. 65, 353 (1990)] concept whereby lattice sites of a periodic structure are occupied by A and B atoms so as to closely reproduce the structural correlation functions of an infinite, perfectly random alloy. Total-energy minimization provides then the relaxed atomic positions while application of the local-density formalism, as implemented by the linearized augmented-plane-wave method, describes self-consistently the consequences of chemical and structural perturbations. We show how these perturbations lead both to (i) distinct A-like and B-like features in the density of states and the electronic charge densities, and even to (ii) different C-like features associated with fluctuations in the local environments around the common sublattice.