Theoretical and Experimental Study of the Electronic and Optical Properties of ZnIn2Se4 Crystals

The electronic properties of ZnIn₂Se₄ crystals have been studied experimentally by spectral ellipsometry and theoretically (from the first principles) using the density functional theory (DFT). Ellipsometric studies in the energy range of 0.7–6.5 eV made it possible to determine the imaginary and real parts of the dielectric function and optical conductivity, as well as the dispersion of the refractive indices, extinction coefficients, and absorption coefficients, and to estimate the values of the Urbach energy, plasma frequency, and nonlinear optical characteristics of ZnIn₂Se₄ crystals. The electronic band structure, origin of energy states, optical functions for incident light polarized along the crystal optic axis and perpendicular to it, and partial densities of states projected onto atoms are determined by ab initio calculations. The theoretical results are compared with the experimental data obtained by spectral ellipsometry.