Photoluminescence properties of high-quality ZnO thin films prepared by an RF-magnetron sputtering method

We have investigated photoluminescence (PL) properties of high-quality ZnO thin films prepared by an RF-magnetron sputtering method. The X-ray-diffraction patterns indicate that the crystalline thin film is preferentially oriented along the [0 0 0 1] crystal axis. By introducing a low-temperature buffer layer and by growing thin films at a high temperature of 600 °C, the crystal quality of ZnO thin films is markedly improved. In addition, we have found that ambience during a cooling process to room temperature after the deposition is another important factor to improve the PL properties; namely, the defect-related PL disappears and the free exciton PL with a sharp width is observed by cooling thin films in the presence of oxygen. Furthermore, under high-density excitation conditions, a PL band due to an exciton–exciton scattering process, the so-called P emission, is observed.