Ab initio calculations and experimental study of the electronic properties of CdGa$_2$S$_4$ single crystals by spectral ellipsometry

The electronic properties of CdGa$_2$S$_4$ single crystals have been studied experimentally using spectral ellipsometry and theoretically from first principles using density functional theory (DFT). Using ellipsometric studies in the energy range of 0.7–6.5 eV, the imaginary and real parts of the dielectric function along and perpendicular to the optical axis, the dispersion of the refractive, extinction, and absorption coefficients are determined. The width of the direct band gap is estimated. The band structure, the origin of the energy states, the optical functions, and the partial densities of states (PDOS) projected onto the atoms are determined by ab initio calculations. The theoretically calculated results are compared with the experimental data of the present work obtained by the method of spectral ellipsometry and with the experimental results available in the literature.