Ab Initio Investigation of Electronic and Optical Properties of Cu-Doped As2S3

The density functional theory with generalized gradient approximation is used to investigate the structural, electronic, and optical properties of Cu0.125As2S3 and Cu0.25As2S3 configurations with copper impurity at c-face center interstitial site. The As -S bond lengths remain nearly the same but Cu -S bond lengths decrease with the increase in copper concentration. Both the configurations show n-type conductivity and strong p-d hybridization in valence and conduction bands. The density of copper d states in the valence band increases with the increase in Cu content. The calculated optical constants are strongly anisotropic up to 10 eV; however, at higher energies the anisotropy diminishes. The broad peaks in the optical constants along E-?||b(?)and c(?)axes are found in the vicinity of 2 eV. However, the peak heights increase and shift toward lower energy with the increase in copper content. Further, the static dielectric constant, refractive index, and reflectivity increase and the optical bandgap decreases with the increase in copper concentration. The comparison of optical constants shows that Cu(0.2)5As(2)S(3) may be as good choice as Ag0.25As2S3 for optical applications.