Effects of Annealing Temperature on the Structural, Optical, and Electrical Properties of ZnO Thin Films Grown on n-Sih100i Substrates by the Sol–Gel Spin Coating Method Aniruddh Bahadur Yadav • Amritanshu Pandey • S. Jit Received: 6 October 2013 / Revised: 21 November 2013 / Published online: 11 July 2014 Ó The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg 2014 Abstract The effects of annealing temperature on the sol–gel-derived ZnO thin films deposited on n-Sh100i 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  10 2 to 8:1  10 4 X 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 1 Introduction The environment-friendly low-cost ZnO material with direct wide band gap energy of *3.37 eV and large exciton binding energy of *60 meV at room temperature has drawn considerable attention in recent years for developing thin film-based nanoscaled devices for elec- tronic [1], gas sensing [2], bio-sensing [3], piezoelectric [4], and optoelectronic [5] applications. The commonly used techniques for fabricating ZnO thin films include sputtering [6], molecular beam epitaxy [7], metal organic chemical vapor deposition (CVD) [8], spray pyrolysis [9], thermal evaporation [10], pulsed laser deposition [11], and sol–gel [12] methods. Among all the above mentioned techniques, the sol–gel is perhaps the simplest and most inexpensive synthesis technique for depositing ZnO thin films of uniform thickness over a large area of the sub- strates [12]. However, the sol–gel-derived ZnO films are often required to process for post-deposition heat treatment for improving the structural, optical, and electrical prop- erties of the films. The effect of post-deposition heat treatment temperature on various structural, optical, and electrical properties of the ZnO thin films prepared by various techniques other than the sol–gel method have been extensively studied in Available online at http://link.springer.com/journal/40195 A. B. Yadav  A. Pandey  S. Jit (&) Department of Electronics Engineering, Centre for Research in Microelectronics, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India e-mail: sjit.ece@iitbhu.ac.in 123 Acta Metall. Sin. (Engl. Lett.), 2014, 27(4), 682–688 DOI 10.1007/s40195-014-0097-4