Effect of deposition time on chemical bath deposited CdS thin films properties

In this work, cadmium sulphide (CdS) thin films are prepared by a simple and inexpensive chemical bath method. The effect of deposition time is investigated. The synthesized film's properties were characterized by X-ray diffraction (XRD), optical transmittance and photoluminescence. The XRD analysis reveals the formation of CdS with hexagonal or cubic phases. The crystallite size is deduced from the XRD analysis. We noticed that the crystallite size varies linearly as a function of the deposition time. Scanning electron microscopy images indicated that the CdS films are composed of spherical grains and the surfaces of these films become more homogeneous and dense with deposition time increase. The UV-visible transmittance spectra revealed that the films high-visible transmittance ranged between 60 and 80%. Furthermore, a significant increase in the optical bandgap value from 2.17 to 2.32 eV as a function of deposition time is noticed. The photoluminescence spectrum of each CdS film shows three emission peaks located at 537.32 nm (2.3 eV), 568.45 nm (2.18 eV) and 692.72 nm (1.79 eV) at room temperature, which may be attributed, respectively, to the transition from the valence band to the conduction band, excitonic transitions, i.e., DAP pairs recombination and DL-VB or CB-AL emissions. The excitonic transitions are predominantly due to the cadmium interstitials (I-Cd) or sulphur vacancies (V-S) defects present in these CdS films.