Properties of transparent conductive ZnO:Al films prepared by co-sputtering

Al-doped ZnO (ZnO:Al) thin films were grown on glass substrates by co-sputtering at room temperature to explore a possibility of low-cost processing for transparent electrodes. The Al content was controlled by varying Al RF power and the effect of Al contents on the properties of ZnO:Al films was investigated. In X-ray diffraction (XRD), only the (0 0 2) peaks were detected indicating that Al doping did not cause structural degradation of wurtzite ZnO. Atomic force microscopy (AFM) showed that the surfaces of the films became rough with increasing Al contents. The lowest resistivity of 6×10 ^-3 Ω cm and the highest carrier concentration of 2×10²⁰ cm^-3 were obtained with the Al content of 2.07 wt% while the average transmittance of the visible light was above 90%. Absorption edges of the films initially blueshifted with increasing Al content and then redshifted, which has good correlation with the measured electrical properties. This work demonstrates a potential that transparent electrodes can be produced using a simple low-cost technique.