Violet and blue-green luminescence from Ti-doped ZnO films deposited by RF reactive magnetron sputtering

Pure and Ti-doped zinc oxide (TZO) films are deposited using radio frequency (RF) reactive magnetron sputtering at different RF powers. Micro-structural and optical properties in doped ZnO films are systematically investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electronic microscopy (SEM), and a fluorescence spectrophotometer. The results indicate that ZnO films show stronger preferred orientation toward the c$c$-axis and smoother surface roughness after Ti doping. As for TZO films, the full width at half maxima (FWHM) of (002) diffraction peaks decreased first and then increased, reaching a minimum of about 0.92° at 150 W, while the residual compressive stress of the TZO film prepared at 150 W became the largest. The photoluminescent (PL) spectra measured at room temperature reveal a violet, a blue and two green emissions. Intense violet and blue-green luminescence is obtained for the sample deposited at higher RF power. The origin of these emissions is discussed.