Abstract:

The effects of annealing temperature on the sol–gel-derived ZnO thin films deposited on n-S〈100〉 substrates by sol–gel spin coating method have been studied in this paper. The structural, optical, and electrical properties of ZnO thin films annealed at 450, 550, and 650 °C in the Ar gas atmosphere have been investigated in a systematic way. The XRD analysis shows a polycrystalline nature of the films at all three annealing temperatures. Further, the crystallite size is observed to be increased with the annealing temperature, whereas the positions of various peaks in the XRD spectra are found to be red-shifted with the temperature. The surface morphology studied through the scanning electron microscopy measurements shows a uniform distribution of ZnO nanoparticles over the entire Si substrates of enhanced grain sizes with the annealing temperature. Optical properties investigated by photoluminescence spectroscopy shows an optical band gap varying in the range of 3.28–3.15 eV as annealing temperature is increased from 450 to 650 °C, respectively. The four-point probe measurement shows a decrease in resistivity from \( 2.1\; \times \;10^{ - 2} \) to \( 8.1\; \times \;10^{ - 4} \) Ω cm with the increased temperature from 450 to 650 °C. The study could be useful for studying the sol–gel-derived ZnO thin film-based devices for various electronic, optoelectronic, and gas sensing applications.

Key words: Nanocrystalline ZnO thin film, Sol–gel, Annealing, Surface morphology, Photoluminescence(PL), Resistivity, Grain size