Low resistivity and high transparent ITO, RuOx (1≤×≤2) and TiW ohmic contacts to ZnO film was achieved by RF sputter system and annealing treatment. The transmittance of 450°C-annealing ITO, 650°C-annealing Ru and 200°C-annealing TiW were measured to be 94, 68 and 61%, with wavelength of 400 nm, respectively. Moreover, the specific contact resistance of 450°C-annealing ITO, 650°C-annealing Ru and 200°C-annealing TiW on ZnO films was estimated to be 2.15×10 -4, 2.72×10-4 and 2.56×10-4 Ω-cm2 by circular transmission line model (CTLM) method, respectively. In the study of ZnO-based photodiodes, high quality and vertical well-aligned ZnO nanowires were selectively grown on ZnO:Ga/glass templates by vapor-liquid-solid method. Ultraviolet (UV) photodetectors using these vertical ZnO nanowires were also fabricated by spin-on-glass technology. With 2 V applied bias, it was found that dark current density of the fabricated device was only 3.8 × 10-9 A/cm2. It was also found that UV-to-visible rejection ratio and quantum efficiency of the fabricated ZnO nanowire photodetectors were more than 1000 and 12.6%, respectively.