Conduction-Band Structures of Wurtzite ZnO Solid Solutions by First Principles Calculations

Abstract

Solid solutions of Zn_1−xCd_xO and Zn_1−xMg_xO (0≤x≤1) with wurtzite structures are systematically investigated by first principles calculations with special interests on the dependence of energetics and electronic structures on the alloy structure. Alloying ZnO with CdO shows a linear increase in the lattice parameters when we choose energetically favorable alloy structures. On the other hand, they do not show such a linear trend when alloyed with MgO. Formation energy with reference to the end-member oxides of wurtzite structures is positive for Zn_1−xCd_xO alloys, whereas it is slightly negative for Zn_1−xMg_xO alloy. They are consistent with the experimental fact that highly concentrated solid solutions are easier to be formed in Zn_1−xMg_xO alloys. The band gap shows a monotonous decrease in Zn_1−xCd_xO and increase in Zn_1−xMg_xO with the solute concentration. In Zn_1−xCd_xO, Cd has an orbital component as large as that of Zn at the bottom of the conduction band. On the other hand, the contribution of Mg is much smaller in Zn_1−xMg_xO. They are consistent with the changes in the band gap with the composition.