Effect of post deposition annealing on sputtered zinc oxide film

High quality crystalline c-axis oriented zinc oxide (ZnO) film has been deposited on various substrates by rf sputtering in pure argon ambient. The effect of post deposition annealing (300 K to 1073 K) on the structural and optical properties of sputtered ZnO thin film have been investigated. It is found from the XRD pattern that the intensity and the grain size increases with annealing temperature and becomes maximum for 1063 K. Also the asymmetric factor approaches to the value of one. The lattice constant and stress as a function of annealing temperature shows that up to 673 K, their is a state of stress relief and above 673 K, it goes in a state of compression. The SEM photograph also demonstrate that the grain size increases with annealing temperature, however, cracks are observed on the surface of the films annealed at 873 K. The optical band gap of the film is found to be a minimum (3.23 eV) for the films annealed at 673 K, whereas refractive index and packing density is at a maximum