Influence of the oxygen partial pressure and post-deposition annealing on the structure and optical properties of ZnO films grown by dc magnetron sputtering at room temperature

A systematic study for the optimization of the deposition process of ZnO thin films grown by dc magnetron sputtering at room temperature was carried out using different oxygen partial pressures and deposition times. We have established a correlation between the oxygen partial pressure, the chemical composition and the crystalline structure of the films. Stoichiometric and highly oriented ZnO thin films along the (0 0 2) crystal plane with very good optical performance were obtained for a relative oxygen gas flow of 20% in the gas mixture. Higher O-2 concentrations resulted in non-stoichiometric ZnO with an excess of oxygen, which exhibited a lower degree of crystallinity and slightly higher band-gap energy. X-ray absorption near edge structure (XANES) analysis indicated that this excess of oxygen was incorporated in molecular form inducing a reduction in the crystallinity of the material. Post-deposition annealing treatments up to 500 degrees C significantly improved their crystallinity as confirmed by x-ray diffraction and XANES. Therefore, it has been found that it is possible to grow ZnO at room temperature with high crystal quality and good optical response by controlling the growth conditions.