Preferentially oriented ZnO thin films on basal plane sapphire substrates derived from polymeric precursors

Preferentially oriented zinc oxide (ZnO) thin films on basal plane sapphire have been deposited by spin coating polymeric precursors synthesized via Pechini process. The polymeric precursors were synthesized using citric acid as chelating agent and ethylene glycol as reaction medium. The effects of annealing (from 673 K to 1273 K) on surface morphology, crystallinity, and optical properties were examined. XRD results illustrate polycrystalline ZnO thin films with preferred orientation along (0 0 2) plane that increases with an increase in annealing temperature. The textured ZnO films were obtained on annealing for 10 min at 1173 K without the formation of interfacial spinels. Surface morphology of these films changed from spherical to highly faceted grains. Transmission spectra reveal that all films are >70% transparent except for the sample annealed at 1273 K, which has 45% optical transparency in the visible region. Room temperature photoluminescence spectra revealed broad ultraviolet emission centered at 380 nm without deep-level emission, suggesting high quality ZnO thin films.