Annealing effect on the microstructure and optical characterization of Zn₂SiO₄ thin film sputtered on quartz glass

A thin ZnO film (approximately 500nm in thickness) was deposited on quartz glass by sputtering a ZnO target (purity of 99.995%) using a radio frequency (RF) power source in the magnetron sputter. Annealing of the specimen at elevated temperatures (i.e., 1000, 1100, and 1200 °C) was conducted to clarify the effects of annealing on the microstructure and optical characteristics of the film. It was found that silicon ions diffused faster than zinc and oxygen ions in the system containing the oxide film and quartz glass substrate Zn₂SiO₄ whose thickness depended on the annealing temperature and duration. The surface and cross-sectional morphologies of the as-sputtered film and films annealed at various temperatures were examined by field emission scanning electron microscopy (FE-SEM) and in more detail by high-resolution transmission electron microscopy (HRTEM). Line scans obtained by scanning transmission electron microscopy (STEM) showed that the composition (wt %) of the film annealed at 1200 °C was Zn (70%), Si (20%), and O (10%). These findings indicated that ZnO completely transferred into the Zn₂SiO₄ film to act as a luminescence center in the case of postannealing at 1200 °C for 2 h. The amounts of ZnO transferred to Zn₂SiO₄ were 38.5% at 1000 °C and 31.1% at 1100 °C for the same duration. The specimens annealed at 1000, 1100, and 1200 °C showed no photoluminescence (PL) emission as determined by measurement.