Studies on ZnO:Al thin films deposited by in-line reactive mid-frequency magnetron sputtering
Al-doped ZnO (ZnO:Al or AZO) films were deposited on glass substrates using an in-line reactive mid-frequency (MF) magnetron sputtering process. The influence of the deposition parameters including oxygen partial pressure and substrate temperature on the surface morphology and electrical, optical and mechanical properties of the films were investigated. The film hardness as determined by a nano-indenter indicate that the crystallinity of the ZnO:Al films was improved with increasing substrate temperature. The films with minimum resistivity could only be deposited under a narrow range of oxygen partial pressure. The carrier concentration, Hall mobility and optical band gap of the ZnO:Al films increased when the substrate temperature was raised from room temperature to 150 °C, and then decreased when the temperature was higher than 150 °C. The film prepared at the substrate temperature of 150 °C exhibited columnar structure with a RMS roughness of 4.4 nm and a lowest resistivity of 4.6×10-4 cm. The transmittance and reflectance spectra with the ellipsometric data were analyzed by using a Drude-Lorentz-Gauss model.