Ab initio investigations of zinc chalcogenides semiconductor alloys

The present work performs self-consistent ab initio full potential-linearized augmented plane wave method to study the structural, electronic and thermodynamic properties of ZnSxSe1−x, ZnSxTe1−x and ZnSexTe1−x semiconductor alloys. The ground-state properties were determined for the bulk materials (ZnS, ZnSe, and ZnTe) and for their alloys in cubic phase at various concentrations (x=0.25, 0.5 and 0.75). A marginal deviation of the lattice parameter from Vegard's law was observed for ZnSxSe1−x and ZnSexTe1−x alloys, while the lattice bowing of ZnSxTe1−x alloy was found to be significant. This is mainly because of the large mismatch of the lattice parameters of the binary compounds ZnS and ZnTe. A large deviation of the bulk modulus from linear concentration dependence was observed for all the three alloys. We have also investigated the effect of composition on bonding properties and correlated it to the charge-exchange effect in the optical bowing. Using the approach of Zunger et al. [21], the microscopic origins of the gap bowing were explained. The disorder parameter (gap bowing) for the alloys of interest was found to be mainly caused by the structural relaxation contributions. The charge-exchange contributions for all the three alloys were also found to be significant. The calculated phase diagram showed a broad miscibility gap for all the alloys of interest with a high critical temperature.