Al-doping effect on structural, transport and optical properties of ZnO films by simultaneous RF and DC magnetron sputtering

Transparent and conductive Al-doped ZnO films have been prepared by simultaneous RF and DC magnetron sputtering. In order to study the properties of the Al-doped ZnO films, we performed X-ray diffraction, X-ray absorption spectroscopy, temperature dependence of electrical resistance and Hall measurements, as well as optical transmission spectroscopy. The results revealed that all the samples were polycrystalline with a strong preferential c-axis orientation. A minimum resistivity of 7.13×10−3Ωcm was obtained, and a metallic-type conducting behavior was observed for the film at 50 W. Our present work suggests that the electrical transport property of the Al-doped ZnO films is closely related to the crystallinity. A large number of defects due to poor crystallinity and the induced stress field are able to immobilize the free carrier thereby reducing the conductivity.