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

7 A systematic study for the optimization of the deposition process of ZnO thin films grown by 8 DC magnetron sputtering at room temperature was carried out using different oxygen partial 9 pressures and deposition times. We have established a correlation between the oxygen partial 10 pressure, the chemical composition and the crystalline structure of the films. 11 Stoichiometric and highly oriented ZnO thin films along the (002) crystal plane with very good 12 optical performance were obtained for a relative oxygen gas flow of 20% in the gas mixture. 13 Higher O2 concentrations resulted in non-stoichiometric ZnO with an excess of oxygen, which 14 exhibited a lower degree of crystallinity and slightly higher band-gap energy. 15 X-ray Absorption Near Edge Structure (XANES) analysis indicated that this excess of oxygen 16 was incorporated in a molecular form inducing the reduction in the crystallinity of the material. 17 Post-deposition annealing treatments up to 500 o C significantly improved their crystallinity as 18 confirmed by XRay Diffraction (XRD) and XANES. Therefore, it has been found that it is 19 possible to grow ZnO at room temperature with high crystal quality and good optical response 20 by controlling the growth conditions. 21