IMPACT OF ANNEALING TEMPERATURES ON SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF REACTIVE SPUTTER DEPOSITED NiO FILMS

Abstract

In this work, the reactive radio frequency magnetron sputtering was used to deposit nickel oxide (NiO) thin films on Al₂O₃/glass substrate at 250 °C. Subsequently, the NiO films were subjected to annealing at different temperatures (300 °C, 350 °C, 400 °C, 450 °C, and 600 °C) in ambient air. The influence of temperature annealing on the crystal structure, surface morphology, and optical properties of NiO thin film was investigated using X-ray diffraction, scanning electron microscopy, and UV-Vis spectroscopy, respectively. The X-ray diffraction analysis reveals that the NiO films exhibit a distinct preference for crystal orientations along the (111) and (200) planes. When the temperature is raised over 450 °C during annealing, the (200) peak disappears and a new (220) peak appears. The scanning electron microscopy images clearly indicate a notable enhancement in surface roughness and a significant improvement in grain size. Furthermore, all of the samples exhibit an average transmittance of 65% across the wavelength range of 400 to 800 nm, as determined by UV-vis spectra. The optical band gap was determined to range from 3.467 to 3.658 eV. Hall measurements reveal the high film resistivity of 1.84 ×10³ to 6.15 ×10³ Ω.cm, which increases in accordance with annealing temperature. This outcome establishes a foundation for utilizing NiO thin films in UV-photodetectors.