Crystal and band structures of ZnS, MgS, and ZnS-MgS alloys

摘要

ZnS-MgS alloys have great potential applications in ultraviolet optoelectronic devices due to their large bandgaps. The structures of ZnS, MgS, and ZnS-MgS alloys are systematically investigated for different compositions and pressures, using first-principles evolutionary simulations. We successfully found the experimentally known structures (B1, B3, and Cmcm for ZnS and B1 for MgS) and the novel stable structures (P4mm for ZnS and P213 and R3 for MgS). The phase-transition pressures are in good agreement with the experimental results. We also predicted the existence of thermody-namically stable ZnS-MgS alloys at high pressures (P4mm-MgZnS2, P21/m-MgZn_3S_4, Pmm2-MgZn_7S_8, and R3-Mg_8ZnS_9) with unusual bonding and electronic properties. Furthermore, we revealed that the structures of Zn-rich alloys are constructed by the supercells of metal P4mm-ZnS, leading to the abrupt band-gap increase with the increase in Mg concentration, whereas the structures of Mg-rich alloys are based on those of R3-MgS and the bandgap decreases as the Mg concentration further increases.