DISORDER EFFECTS ON THE DENSITY OF STATES OF THE II-VI SEMICONDUCTOR ALLOYS HG0.5CD0.5TE, CD0.5ZN0.5TE, AND HG0.5ZN0.5TE

The electronic structure of substitutionally random A1-xB(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 electronic mismatch 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 Hg0.5Cd0.5Te, Cd0.5Zn0.5Te, and Hg0.5Zn0.5Te 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.