Electronic Structures and Optical Properties of Cu-based Semiconductors with Chalcopyrite-type Structure

chThe density functional theory(DFT) based on the pseudo-potential plane wave basis was employed to investigate the geometries, electronic structures, linear and second-order nonlinear optical properties of the CuXY2(X= Ga, In; Y=S, Se, Te) crystals with chalcopyrite structure. The results indicate that these compounds are semiconductors with a direct gap and have similar band structures. The static dielectric constants, the refractive indices and the second harmonic generation(SHG) coefficients(d(36)) of these compounds in. crease in the sequence of S -> Se -> Te for the same X atom. Among the occupied bands, those states near the top of the valence band contribute mostly to the SHG effect, which are dominated by the components of Cu-3d orbitals and the valence p orbitals of Y atom. While for the unoccupied bands, the bands mainly derived from valence p orbitals of X atoms have obvious influences on the SHG coefficient. Among these six crystals, CuInSe2 has high photoconductivity and better absorption of sunlight. In addition, CuGaS2 and CuGaSe2 crystal have potential applications in the second-order nonlinear optical fields based on their birefringences and SHG strengths.