Structure, optical properties, and electrical properties of low copper-doped cadmium oxide thin films for optoelectronic applications

Abstract

This study utilized spray pyrolysis to fabricate CdO films, both undoped and doped with varying concentrations of Cu (0%, 1%, 2%, 3%, 4%, and 5%). The polycrystalline cubic nature of the materials was confirmed through XRD examination. Rietveld refinement was employed to determine the lattice constant. Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy, and X-ray spectroscopy (XRS) were employed to elucidate the chemical composition of the materials. The structure, morphology, optical, and electrical properties of the films were comprehensively investigated using XRD, scanning electron microscopy (SEM), UV–visible spectrophotometry, and Hall effect measurements. A comparison is made between the calculated absorption edge ($E_{d}^{opt}$) obtained from the peak of absorbance derivative spectra and from the absorption coefficient derived from Tauc relationship (at α = 10⁴ cm⁻¹). It was found that the absorption edge does not significantly differ between the two calculating methods. The optical band gap was calculated in terms of Kubelka–Munk function and the Tauc relationship. It can be observed that there is a negligible difference between the two methods. The optical band gaps ($E_{d}^{opt}$) of the CdO: Cu films were observed to decrease with increasing Cu doping levels. Additionally, effective Cu doping was found to enhance the electrical characteristics of CdO, as evidenced by the film's 3% resistivity. The carrier concentration was approximately 5 × 10²⁰, compared to 2.25 × 10²⁰ for the undoped film, while the level of Cu doping was approximately ten times that of the CdO film. Cu-CdO films exhibit the potential to be utilized as Transparent Conducting Oxide (TCO) materials, offering improved optical and electrical properties for various optoelectronic device applications.