Effect of Cu incorporation on the physical properties of CdS thin films deposited by using the thermal evaporation technique

CdS thin films with different Cu concentrations were grown on glass substrates at room temperature by using the resistive thermal evaporation technique. The effect of Cu doping on the structural, optical and vibrational properties of CdS thin films was investigated. The structural, optical and vibrational analysis was completed using an X-ray diffractrometer and a Raman and a UV-VIS-NIR spectrophotometer. X-ray diffraction data revealed that incorporation of Cu ions improved the crystalline structure but did not change the cubic phase of the CdS thin film with a preferential orientation along the (111) direction. Various optical parameters, like the refractive index, extinction co-efficient, absorption co-efficient, urbach tail energy E_e and optical band gap, were determined by using transmission data at different copper concentrations. The Raman peaks appearing at 299 cm^‑1 and 592 cm^‑1 for CdS were attributed to the 1LO and 2LO phonons of cubic CdS, and a shift towards low wavenumber region was observed with increasing Cu concentration.