Violet luminescence emitted from ZnO films deposited on Si substrate by rf magnetron sputtering

Highly orientated polycrystalline ZnO films have been deposited on Si substrate at room temperature (RT) by rf magnetron sputtering. A strong violet photoluminescence (PL) located at 402 nm and a weak ultraviolet (UV), PL located at 384 nm are observed when excited with 300 nm light. The former PL originated from the electron transition from conduction band tail states to valence band tail states and the latter is produced due to electron transition from conduction band to valence band. With an increase in intensity of the excitation light, the violet emission peak increases super-linearly and the UV emission increases linearly. After high temperature annealing in air, the crystallinity of obtained films is improved, the violet emission becomes weak and the UV emission gets strong.