Effect of the oxygen partial pressure on the properties of ZnO thin films grown by metalorganic vapor phase epitaxy

ZnO thin films were grown on c-plane sapphire substrate at 600°C by metalorganic vapor phase epitaxy (MOVPE). The effect of one of the main deposition parameters, the oxygen partial pressure, on the properties of the ZnO thin films was investigated by means of X-ray diffraction (XRD), photoluminescence (PL) spectrum, atomic force microscopy (AFM) and Hall measurements. Increasing the oxygen partial pressure up to 65 Pa was found to degrade the crystallinity of the ZnO thin films because of the formation of the oxygen-induced defects, but the UV emission in PL spectra was enhanced and deep level emission was weakened. It might be attributed to the reduction of the oxygen vacancies concentration. So the UV emission might be more dependent on the stoichiometry than the microstructural quality of the ZnO thin films. At the same time, Hall measurements showed that the electrical resistivity of the ZnO thin films increased with the oxygen pressure and the electron mobility decreased. The origin of n-type character in undoped ZnO films was the oxygen vacancies.