Impact of structural defects on the electronic and optical properties of Pb4Ga4Ge(S, Se)12 crystals

The influence of the synthesis process on structure defect and electronic properties were investigated through the analysis of phase diagrams of PbGa2Ge(S)S & iecy;6-Pb4Ga4Ge(S)Se12 systems, temperature band-gap dependence, detailed measurements of the electronic structure using the X-ray photoelectron and emission spectroscopy techniques and employing ab-initio calculations. Theoretical studies of two isostructural non-centrosymmetric crystals Pb4Ga4Ge(Se,S)12 were performed within a density functional theory framework. Electronic structure and optical properties were simulated from the first-principles for perfect and imperfect crystals with vacancytype defects. Band-gap and optical function showing strong dependence on different chalcogen atoms and structural defects. The presented results help to determine the impact of S substitution for Se on the electronic structure and conditions for the formation of defects and also provide better understanding the structureproperty relationship for real crystals, which gives the better opportunities to predict properties of potential crystals that finally result in limiting the experimental attempts only to promising compounds.