ELECTRONIC STRUCTURE AND OPTICAL PROPERTIES OF QUATERNARY CHALCOGENIDES AgIn0.5Ga0.5Se2 AND CuIn0.5Ga0.5Se2 BY FIRST-PRINCIPLES CALCULATIONS

In this work, by performing first principles calculations within generalized gradient approximation (GGA) based on Density Functional Theory (DFT), the band structure and optical-related properties of quaternary metal chalcogenides AgIn0.5Ga0.5Se2 and CuIn0.5Ga0.5Se2 are presented. The energy gap is found to be direct of 0.177 and 0.011 eV for the two materials, respectively. The differences of the complex dielectric functions, the absorption spectra and the reflectivity coefficients of AgIn0.5Ga0.5Se2 and CuIn0.5Ga0.5Se2 are discussed. It follows that the electronic configurations of monovalent X (X = Ag, Cu) cations are responsible for the different electronic and optical properties of XIn0.5Ga0.5Se2.