Synthesis and characterization of zinc cobalt sulphide nanofilms for optoelectronic applications

Zinc-cobalt sulphide (${\text{Zn}}_x{\text{Co}}_{1-x}S$) thin films were fabricated on glass substrates using the chemical bath deposition (CBD) technique. In this study, the films were grown employing solutions of zinc acetate, cobalt sulphate, and thioacetamide as the respective sources of zinc, cobalt, and sulphur. The synthesized films were investigated for their potential use in optoelectronic device applications. Optical characterization revealed that the films exhibited a direct transition with an energy gap ranging from 3.350 to 3.360 ​eV. As the zinc concentrations were changing, the absorbance of the films were decreasing uniformly along the wavelength spectra. The films exhibit a low extinction coefficient (0.0–0.23) that may be due to the internal reflections within the material as concentrations changes. Variations in the thickness, reflectance and refractive index with zinc concentrations were also discussed. The electrical resistivity was found to decrease from $7.12\times {10}^8$ to $5.94\times {10}^8$ (Ω.cm) with zinc concentrations. According to the crystallography spectrum, ${\text{Zn}}_x{\text{Co}}_{1-x}S$ has a polycrystalline structure with various distinct peaks at different orientations. Scanning electron microscopy shows that surface morphology of ${\text{Zn}}_x{\text{Co}}_{1-x}S$ films has a well-defined nanoparticles of different shapes and sizes which are uniformly distributed and are significantly transformed as a function of concentrations. The results demonstrate that the chemically deposited thin films can be engineered for a range of optoelectronic applications.