Electronic band structure of AgCd2GaS4:: theory and experiment

We report theoretical calculations of the band structure of AgCd2GaS4 using the full-potential linear augmented plane wave method and experimental measurements of the valence band x-ray photoelectron spectroscopy. We find that the valence band maximum and the conduction band minimum are located at the Gamma point of the Brillouin zone resulting in a direct energy gap of 1.0 eV compared to our measured experimental value of 2.15 eV. Our analysis of the partial density of states shows that there is a weak covalent interaction between Ag and Ga atoms and between Ag and Cd atoms, and a substantial covalent interaction between Ag and S atoms. Thus the Ga-Ag and Cd-Ag bonds are basically of ionic character, and Ag-S bonds are of covalent character. The theoretical results of the density of states are in agreement with the valence band x-ray photoelectron spectroscopy measurements with respect to spectral peak positions. We have analyzed the calculated density of states and find a strong/weak hybridization between the Ag, Cd, Ga and S states in the valence and conduction bands.