Effect of direct current power to Ti-target on the composition, structure and characterization of the Ti (0-2.36 at. %), Al codoped ZnO sputtering thin films

Transparent conductive Ti, Al codoped ZnO (TAZO) films were prepared on glass substrate by three-target magnetron sputtering system in this work. The glass substrate was heated to 200 °C, and the working pressure in the chamber was at 5 × 10^-2 Torr. In the process of sputtering, pure Ti target was bombarded by direct current varying in the power at 0, 20, 30, and 40 W; however, the pure Al target and pure ZnO target were bombarded by radio frequency power fixed at 100 W. After sputtering for 150 min, the thickness of the films was measured to be about 700nm varying in Ti-content. The surface morphology and cross section of the films were examined by using field emission scanning electron microscope (FE-SEM) and their composition was analyzed with attached energy dispersive spectroscopy (EDS). The Ti-content of the films was found to increase with increasing the DC power in the order: 0 at.% (0W) < 0.59 at.% (20 W) < 1.35 at.% (30 W) < 2.36 at.% (40 W). Analysis of X-ray diffraction (XRD) indicated that all the films belong to wurtzite structure textured on (0002). Through examination by atomic force microscopy (AFM), the films revealed their average surface roughness (R _a) decreased from 10.74 to 5.40nm with increasing the Ti-content. Surface composition and depth profile of the films were examined by X-ray photoelectron spectroscopy (XPS). The electrical resistivity of the films, determined by four-point probe, was in the range from 0:93 × 10 ^-3 Ωcm (with 0.59 at.% Ti) to 8.34 × 10^-3 Ωcm (with 2.36 at.% Ti). The average optical transmittance of the films analyzed by UV-vis light was higher than 85% in visible spectra.