Physical Properties of Nanostructured Zinc Sulfide Thin Films Deposited by the PLD Method for Gas Sensing

Abstract

The pulsed laser deposition (PLD) technique created nanostructured semiconducting zinc sulfide (ZnS) thin films onto a quartz substrate. A gas sensing static unit, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD) were used to analyze the structural, surface morphology, and gas sensing properties of the as-deposited thin films. After the ZnS thin films were formed, they were heated to evaluate the effects of annealing on the characteristics of the ZnS film. XRD analysis reveals that the ZnS thin films exhibit a structure similar to zinc blend cubes, with a preference for the (111) orientation. The X-ray diffraction (XRD) patterns that emerge during annealing show that ZnS thin films become more crystalline. Grain size increases as the annealing temperature rises. Images captured by field emission scanning electron microscopy (FESEM) revealed a grain-like sphere for each of the annealed thin films, confirming the growth of grains. The UV-Vis spectra showed that the ZnS samples' transmittance boosts after annealing because their crystalline quality is improved. The transmittance is measured within the 400 ̶ 900 nm band, and the optical band gap is direct at 3.72 eV, decreasing to 3.51 eV at 350 °C during annealing. Annealing significantly improves the physical properties of ZnS thin films, according to all presented data. NO₂ and CO₂ gas were used to obtain the I-V values ​​of the samples. The ability of ZnS thin films formed at different annealing temperatures was tested using NO₂ gas. The sensors were fabricated and tested at different operating temperatures and NO₂ gas concentrations of 100, 300, 400, 500, and 700 ppm.