Effect of annealing temperature on the structural and optical properties of ZnO thin films prepared by RF magnetron sputtering

ZnO thin films were deposited on corning glass substrates by RF magnetron sputtering at room temperature. The dependence of crystal structure, morphology and optical properties on post-deposition annealing was investigated using XRD, AFM and UV–vis Spectrophotometer. The as-deposited films were amorphous in nature. Post-deposition annealing for 1 h in air caused an improvement in crystallinity with preferential orientation along (0 0 2) direction. Better crystallinity was observed at 673 K. Crystallite size increased from 16 to 27 nm as annealing temperature was increased from 473 to 873 K. It is evident from AFM analysis that rms roughness of the film annealed at 673 K is minimum indicating better optical quality. Optical measurements show a decrease in direct band gap from 3.289 (as deposited) to 3.25 eV when the annealing temperature was increased to 673 K. With further increase in temperature, band gap increases.