First-principles study of the energy-gap composition dependence of Zn_1−xBe_xSe ternary alloys

We report the results of a self-consistent pseudopotential study including structural, optical, and thermodynamic properties of cubic Zn_1−xBe_xSe semiconductor alloy. The system is modeled in various possible configurations using a large 64-atom supercell. The evaluated band-gap bowing is in good agreement with the experimental data. The different roles of structural and chemical effects on the gap bowing and its variation with composition are identified and discussed. It is found that structural effect, i.e., the relaxation of atomic bonds, overwhelms the other contributions to the gap bowing. Lattice parameter fulfills Vegard’s law with a small downward bowing deviation of about 0.04 Å. Our calculated bond lengths appear to be more reliable compared with those obtained from previous theoretical studies using smaller atomic supercell. Besides, a regular-solution model was used to investigate the thermodynamic stability of Zn_1−xBe_xSe, which mainly indicates a wide phase miscibility gap.