Influence of oxygen argon ratio on the structural, electrical, optical and thermoelectrical properties of Al-doped ZnO thin films

In this study, high quality of Al-doped ZnO (AZO) thin films were deposited at different oxygen argon ratio by direct current (DC) reactive magnetron sputtering using a Zn target (99.99%) containing Al of 1.5%. The obtained films were characterized and analyzed by X-ray diffraction (XRD) and ultraviolet–visible and infrared light spectrophotometer. The electrical properties had been investigated by van der Pauw method. It was also found that oxygen argon (O2/Ar) ratio had great influence on the properties. The results show that AZO thin films are polycrystalline with a preferred (0 0 2) orientation. The film stress increases with increasing O2/Ar ratio. The lowest resistivity of 1.306×10−3 Ω cm was obtained for the AZO thin films prepared at O2/Ar ratio of 0.3/27. Hall mobility decreases with increasing the O2/Ar ratio. With increasing O2/Ar ratio, the transmittance of the AZO thin films has no evident changes. There is a strong absorption in the ultraviolet region. The optical absorption edge is found to shift to the longer wavelength with the increase of O2/Ar ratio. The measurements show that there is a striking Seebeck effect in the AZO thin films, and their thermoelectromotive force is linearly increased with increasing temperature difference (ΔT). With increasing O2/Ar ratio and resistance of samples, thermoelectric power (TEP) decreases.