Microstructures and optical absorption of Ti-doped ZnO films

Undoped and Ti-doped ZnO films were deposited using radio frequency reactive magnetron sputtering at various sputtering powers. The crystal structures, surface morphology, chemical state of titanium, zinc, and oxygen and optical properties in Ti-doped ZnO films were systematically investigated via X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ultraviolet visible (UV-Vis)spectrophotometer. ZnO films showed a stronger preferred orientation toward c-axis and became smoother after Ti doping. The intensity of Ti-doped ZnO (002) peak further increased and surface showed more lattice defects as sputtering power increased from 100 W to 150 W. The XPS spectrum confirmed that Zn exists only in the oxidized state and the sample is a mixture of ZnO and TiO₂. In addition, the UV absorption edge of ZnO films shifted to a longer wavelength as sputtering power increased.