Electronic and optical properties of Mg_xZn_1-xO and Cd_xZn_1-xO from ab initio calculations

Isostructural and heterostructural pseudobinary Mg_xZn _1-xO and Cd_xZn_1-xO alloys are studied by combining the wurtzite and the rocksalt polymorphs within a cluster expansion. The computationally demanding calculation of the quasiparticle electronic structure has been achieved for all cluster cells of the expansion using the recently developed HSE03 + G₀W₀scheme. These results are used to compute the configurational averages for the fundamental band gaps and the densities of states. A strongly nonlinear behavior of the band gaps is observed and it is quantified by means of the corresponding bowing parameters for both material systems. In order to calculate the macroscopic dielectric functions, including excitonic and local-field effects for iso- and heterostructural Mg_xZn_1-xO alloys as well as wurtzite (wz) Cd_xZn_1-xO, the Bethe-Salpeter equation has been solved for each of the corresponding clusters. The respective configurational averages indicate that the composition-dependent variation in the exciton peaks allows conclusions on the alloy composition and preparation conditions.