Characterization of Enhanced Crystalline Structures of CdS Thin Films Deposited by Chemical Bath Deposition Caused by Doping with (Cu²⁺, Ag⁺, Au⁺) Transition Metal Ions

Abstract

In this work, the optical and structural properties of the modified crystalline structures of the nanostructured cadmium sulphide (CdS) semiconductor caused by doping with (Cu2+, Ag+, Au+) transition metal ions are studied. Using the chemical bath deposition technique, thin CdS films of good crystalline quality were deposited, which were doped in synthesis without the need for additional steps, obtaining thicknesses of around 100 nm. The chemical binding energies and their interactions of the CdS semiconductor compound with the different transition metal ions were determined by X-ray photoelectron spectroscopy. The crystalline and quality phase of the CBD-CdS thin films were determined by X-ray diffraction that were confirmed by Raman scattering, obtaining that the dominant crystalline phase is zinc blende in the (1 1 1) crystalline direction. A change in crystalline quality from monocrystalline to polycrystalline was observed by XRD in the CdS thin films doped with transition metal ions, keeping the crystalline direction (1 1 1) of the zinc blende phase of CdS as the dominant one; this crystalline behaviour was confirmed by HRTEM micrographs, in addition to the different levels of quantum confinement favoured by each transition metal incorporated into the CdS. By Raman scattering measurements, the crystalline zinc blende phase of CdS was confirmed and also allowed the analysis of the phononic interactions of the binary compound, where Raman shifts provided information on the structural quality and also confirm the effects of quantum confinement. UV-visible optical spectroscopy describes the effects of the crystalline structural modifications with blue shifts on the optical band gap energies of the evaluated CdS samples, related with the different levels of quantum confinement given by the (Cu2+, Ag+, Au+) transition metal dopants.