Characterization of degenerate Zn-doped CdO thin films for optoelectronic devices

Thin films of pure and zinc-doped cadmium oxide (CdO) were fabricated utilizing the spray pyrolysis method on glass substrates. An extensive analysis was conducted encompassing structural, morphological, compositional, optical, and electrical aspects of these films. Powdered X-ray diffraction (XRD) analysis unveiled that the deposited thin films possessed face-centered cubic structures characteristic of monteponite CdO. Scanning electron microscope (SEM) images depicted distinct crystalline morphologies among the nanoscale thin films, varying with the dopant concentration. Energy-dispersive X-ray spectroscopy (EDS) spectra confirmed the presence of Cadmium (Cd), Zinc (Zn), and Oxygen (O) in the samples. Optical absorption spectra indicated an escalating absorption trend with increasing Zn⁺² doping. Moreover, the optical band gap was higher for Zn-doped CdO thin films, reaching 2.71 eV for 1-wt% Zn, compared to 2.58 eV for pure CdO. Refractive index and photoconductivity properties exhibited significant dependency on the doping concentration. Electrical characteristics, evaluated via Van der Pauw Hall effect measurements, revealed a notable decline in electrical resistivity with escalating zinc doping levels. Consequently, the films exhibited advantageous degenerate semiconductor properties. PL spectra displayed an enhanced visible emission at 470, 575, and 630 nm with Zn²⁺ doping, which interprets the defect density in CdO by occupying Cd²⁺ vacancies with Zn²⁺ ions.