THE ELECTRONIC BAND STRUCTURE AND DIELECTRIC RESPONSE FUNCTION OF ZnGa2S4 and ZnGa2Se4

ZnGa2S4 and ZnGa2Se4 have the vacancy defect stannite structure, belonging to the II-III2-VI4 family of compounds. These materials have been investigated via density functional theory (DFT). The electronic band structure, total and partial density and of states were computed using the LDA+U technique while the dielectric function calculations were performed using norm-conserving pseudopotentials. The band structure calculation showed the materials have indirect band gap of 2.65 eV and 1.82 eV for ZnGa2S4 and ZnGa2Se4 respectively. It was found that the top valence sub band for both compound have comparable energy width 0f 5.9 eV and 6.0 eV forZnGa2S4 and ZnGa2Se4 respectively. The partial density of states calculations showed the top valence band for ZnGa2Se4 to be predominantly of Se-4p states, while the bottom of the conduction band is dominated by Ga-4s state. For ZnGa2S4, the top of the valence sub band is made up of mostly S-3p states, and the conduction band minimum is mainly of Ga-3d and Ga-4s states. The calculated The calculated Ԑ1(0) for ZnGa2S4 and ZnGa2Se4 is 19 and 9 respectively.