A comprehensive study of structural, optical and electrical properties of Cu doped CdS nanocrystalline thin films: for optoelectronic applications

In this work, good quality nanocrystalline cadmium sulphide (CdS) thin films were deposited on the suitably cleaned glass slides with different Cu-doping concentrations using the sol-gel spin-coating technique. The effect of Cu doping on the structural, Raman spectra, optical, electrical, photoluminescence, and photoconductivity properties of the fabricated films was studied. The structural properties of the films were investigated using XRD spectra. The X-ray diffraction results indicated that the crystallite size of Cu-doped nanocrystalline CdS thin films was smaller than that of undoped CdS and the cubic zinc blende structure of the films was observed. Raman scattering was utilized to investigate the optical properties of nanocrystalline CdS thin films and reveal the existence of two main peaks 303 and 604 cm(-1) which are very close to the standard LO frequency. The optical characterization of the films was carried out from optical transmittance and absorption obtained by a double-beam spectrophotometer in the wavelength range from 400 to 800 nm. UV-visible spectroscopy depicts the enhancement of the optical band gap of Cu-doped nanocrystalline CdS thin films compared to the bulk CdS, as a result of the quantum confinement effect. Photoluminescence spectra of the films reveal the occurrence of blue band emission and an increase in emission intensity with Cu-doping concentration. The change of the electrical resistivity and conductivity of the deposited films with temperature was also investigated. A decrease in resistivity and increase in electrical conductivity was detected as increasing Cu-doping in CdS. The dark and photocurrents and photosensitivity of the films were found to be increased linearly with increasing voltage and doping concentration.