Microstructural evolution of sputtered ZnO thin films with rapid thermal annealing

Zinc oxide thin films were deposited on silicon substrates by reactive RF magnetron sputtering technique. Post-deposition rapid thermal annealing of the sputtered thin films was carried out by varying temperatures, annealing duration and oxygen flow rate. The films, annealed at 1000 °C for 150 s in air ambient, have shown highest degree of crystallinity. The surface of the ZnO films, annealed for longer period, was greatly modulated with the evolution of porous surface. The films annealed in oxygen ambient have shown smoother morphology with the reduction in surface roughness. The characteristic absorption band of Zn–O became prominent due to the increase in Zn–O bond density during rapid thermal annealing process. A significant reduction of the deep level emission in the photoluminescence spectra was observed for annealed samples, whereas the near band edge ultraviolet emission was suppressed for the films annealed in oxygen ambient due to the oxygen adsorption at the film surface.