Effects of Annealing on the Optical and Structural Characterization of Spray-Pyrolysed Semiconductor NixZn1-xS Nanostructure Thin Films for Optoelectronic Applications

Abstract

Nickel-doped Zinc Sulfide (NixZn1-xS) semiconductor materials are widely used in optoelectronic devices; however, the effects of post-annealing temperature on their properties have not been previously reported. This study investigates the impact of annealing temperature on the structural and optical properties of NixZn1-xS nanostructured thin films, synthesized using a cost-effective Chemical Spray Pyrolysis (CSP) technique. NixZn1-xS films with a thickness of 320 nm and a mole ratio of x = 0.08 were deposited on hot glass substrates at 250 °C. The precursor solutions consisted of nickel acetate, zinc acetate, and thiourea. We examined the influence of annealing temperatures of 300 °C, 400 °C, and 500 °C on the films, employing X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Ultraviolet-visible spectroscopy (UV-Vis) for characterization. XRD analysis confirmed that all samples exhibited a cubic structure with a unit cell parameter of a = 5.4090 Å and a density of 4.082 g/cm³. The calculated grain sizes for films annealed at 300 °C, 400 °C, and 500 °C were approximately 4.23 nm, 6.40 nm, and 9.54 nm, respectively. SEM images indicated improved surface homogeneity and crystallinity with increased annealing temperature. Optical characterization revealed direct band gaps of 3.82 eV, 3.6 eV, and 3.04 eV for the respective annealing temperatures, with enhanced optical transmittance and reflectance at 500 °C. The decrease in band gap with increased temperature is attributed to improved crystallinity, indicating that annealing enhances the transmittance and overall quality of the semiconductor thin films, making them suitable for optoelectronic applications.