Investigation of structural, optical and electrical properties of Cu doped β-In₂S₃ thin films

β-In₂S₃ thin films with different concentrations of Cu incorporation have been grown on glass substrates using vacuum thermal evaporation method. The influences of the Cu incorporation on the structural, optical and electrical properties of In₂S₃ thin films have been investigated. X-ray photoelectron spectroscopy study suggests the incorporated Cu will exist as Cu⁺ or Cu⁰. XRD analyses reveal that Cu doping will neither change the structure of In₂S₃ nor lead to any formation of new crystalline compounds. Scanning electron microscope views show that the surfaces of the films are flat and dense, and that the grain size increases after Cu doping. The refractive index n of the In₂S₃ thin films which is extracted from spectroscopic ellipsometry measurements shows a slight reduction in the long-wavelength region and a little enhancement in the short-wavelength region after Cu doping. It is also found that the band gap of the thin films is indirect and slightly increases from 1.90 to about 2.02 eV after Cu doping. Electrical measurements indicate that the incorporation of Cu will lead to n-type doping and a decrease of resistivity of the thin films.