Investigation of the Annealing and Cu Doping Effect on Structural and Optical Properties of CdZnS Nanomaterial Deposited by Ultrasonic Spray Pyrolysis

This study investigates doped CdZnS thin films synthesized through the ultrasonic spray pyrolysis technique, followed by annealing at temperatures of 400 and 500 °C. X-ray diffraction analysis demonstrated that both undoped CdZnS and Cu-doped CdZnS thin films exhibit cubic crystal structures, with a preferred orientation along the (111) plane. Scanning electron microscopy (SEM) measurements indicated that the CdZnS thin film has a smooth surface, whereas the Cu-doped CdZnS film shows clustered particles, attributed to the effect of copper doping acting as an activator metal ion. Electron dispersive scanning (EDS) analysis confirmed that the Cd, Zn, and S elements are present in acceptable chemical stoichiometry (Cd + Zn/S = 1:1), with a ratio of 3:1, consistent with the molar amounts used in the precursor solutions. The band gap of the CdZnS thin film decreased from 3.12 to 2.56 eV after annealing at 500 °C, attributed to an increase in crystal size. In contrast, the band gap of the Cu-doped CdZnS thin film decreased from 2.51 to 2.22 eV, lower than that of pure CdZnS, due to the formation of additional phases such as zinc oxide and copper oxide within the CdZnS host structure during annealing.