Photoluminescence of as-grown and annealed ZnO films on Ti-buffered Si (111) substrates

ZnO thin films with strong c-axis preferred orientation have been deposited on Ti buffered Si (111) substrate by reactive ratio-frequency magnetron sputtering. With X-ray diffraction analysis and photoluminescence (PL) measurement, the structure, residual stress and PL emission properties of Ti-buffered ZnO films are studied and effects of Ti-layer thickness and annealing temperature are discussed. It is found that the PL properties of the films are improved after the introduction of Ti buffer layer and an optimized thickness of Ti buffer layer is given. Annealing treatment can improve the properties of Si(111)/Ti-buffer/ZnO films further. The residual stress is found to be an important factor influencing the emission properties of ultraviolet light. It is helpful for the emission of ultraviolet light if the films have a small residual stress. The residual stress can also change the transition energy of excitons. With the increase of annealing temperature, the increase of tension strain in films reduces the band gap of ZnO, hence results in the shift of the excitonic peak to lower energy.