Influence of nitrogen doping on the properties of ZnO films prepared by radio-frequency magnetron sputtering

In this study, zinc oxide thin films were prepared through magnetron sputtering on alkali-free borosilicate glass substrates, with a direct current plasma system adopted to increase the degree of dissociation of N2 gas. The N2/(Ar + N2) flow ratio was varied from 0 to 0.7 during the preparation process to investigate its influence on the properties of the ZnO films. All of the ZnO thin films grew along the preferential (002) crystal plane, with the diffraction intensity of the (103) plane increasing upon increasing the N2/(Ar + N2) flow ratio. The transmittance, as well as the optical band gap, in the wavelength range of visible light (400-700 nm) decreased upon increasing the N2/(Ar + N2) flow ratio. By doping nitrogen at a N2/(Ar + N2) flow ratio of greater than 0.2, the conduction behavior effectively became p-type; nevertheless, the resistivity increased upon increasing the N2/(Ar + N2) flow ratio, due to the increasing Vo concentration and the decreasing grain size of the ZnO films. Among the ZnO films, the film grown at a N2/(Ar + N2) flow ratio of 0.3 exhibited the optimal performance for application as a transparent conducting oxide.