Conductivity enhancement and semiconductor–metal transition in Ti-doped ZnO films

Ti-doped ZnO films were deposited onto Corning 7059 glass substrates by simultaneous RF sputtering of Zn and DC magnetron sputtering of Ti. In this work, X-ray diffraction (XRD), electrical resistivity, X-ray absorption spectroscopy (XAS), optical transmission spectrum, and Hall-effect measurements were utilized in order to study the properties of the Ti-doped ZnO films. The resistivities of the ZnO: Ti films were reduced to a value of 3.82 × 10−3 Ω cm, and a metallic conduction behavior was observed in the ZnO: Ti films with Ti = 1.3%. The enhancement of conductivity and the semiconductor–metal transition are likely attributed to the increase in the free carrier concentration, along with the band-gap shrinkage effects caused by Ti doping.