Effects of thermal annealing on ZnO films grown by plasma enhanced chemical vapour deposition from Zn(C₂H₅)₂ and CO₂ gas mixtures

To improve ZnO thin film quality, the ZnO thin films grown on silicon (100) by plasma enhanced chemical vapour deposition from Zn(C₂H₅)₂ and CO₂ gas mixtures at a low temperature of 120°C are annealed in an oxygen ambient at temperature ranging from 600°C to 1000°C. X-ray diffraction spectra indicate that ZnO films possess a polycrystalline hexagonal wurtzite structure. Atomic force microscopy results show an increase of ZnO grain size with the increase of annealing temperature. The photoluminescence is closely related to the annealing temperature. The free exciton binding energy deduced from the temperature-dependent PL spectra is about 59 meV for the ZnO film annealed at 900°C, suggesting that the film quality can be improved by annealing process.