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 Cu doped Cu_0.125As₂S₃ and Cu_0.25As₂S₃ configurations with Cu impurity at c‐face centre interstitial site. The As‐S bond lengths remain nearly the same but Cu‐S bond lengths decrease with increase in Cu concentration. Both the configurations are n‐type semiconductors which agree with the experimental observations. The density of Cu d states in the valence band increases with increase in Cu content. There is strong p‐d hybridization in valence and conduction bands in both the configurations. The calculated optical constants are strongly anisotropic upto 10 eV, however at higher energies the anisotropy diminishes. The broad peaks in the optical constants along || and axes are found in the vicinity of 2 eV. However, the peak heights increase and shift towards lower energy with increase in Cu content. Further static dielectric constant, refractive index and reflectivity increase and the optical band gap decreases with increase in Cu concentration. The calculated optical band gap is more close to the experimental value for Cu_0.25As₂S₃ configuration. The comparison of optical constants shows that Cu_0.25As₂S₃ may be as good choice as Ag_0.25As₂S₃ for optical applications.

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