Electronic, optical and thermoelectric properties of SnGa2GeX6 (XÂ =Â S, Se) compounds

Electronic, optical and thermo-electric properties of two quaternary chalcogenides SnGa2GeX6 (X = S, Se) have been studied by using density functional theory. Modified Becke-Johnson exchange potential (mBJ-GGA) was used to calculate the band gaps of these compounds. Both compounds show pseudo direct band gap of 1.74 and 1.24 eV for SnGa2GeS6 and SnGa2GeSe6, respectively. The band gap decreases when replacing the X cations from S to Se. The optical properties such as dielectric function, energy loss function, extension coefficient, refractive index, and reflectivity of these compounds are discussed in details. The thermo-electric properties are studied using Boltzmann statistics through BoltzTrap code. High absorption peaks and figure of merits (ZT) for both compounds reveal that they are good candidates for the optoelectronics and thermo-electric devices.