Ab Initio Calculations and Experimental Spectral Ellipsometry Study of the Electronic Properties of CuInS2 Crystals

The electronic properties of CuInS₂ crystals have been investigated experimentally (by spectral ellipsometry) and theoretically (ab initio, using the density functional theory (DFT)). Based on the ellipsometric study in the energy range of 0.7−6.5 eV, the imaginary and real parts of the dielectric function and optical conductivity, dispersion of the refractive indices, and the extinction and absorption coefficients were determined. The values of the Urbach energy, plasma frequency, and nonlinear optical characteristics of CuInS₂ crystals were estimated. The electronic band structure, the origin of energy states, the optical functions for the incident light polarized along and perpendicular to the optical crystal axis, and the partial densities of states (PDOS) projected onto atoms were determined from ab initio calculations. The theoretically calculated results are compared with the spectral ellipsometry data.