Ultraviolet Photodetectors Based on Anodic TiO2 Nanotube Arrays

Anodic TiO2 nanotube arrays prepared by electrochemical anodization were used to fabricate ultraviolet (UV) photodetectors. The devices annealed at 450 degrees C exhibit the highest UV-sensitive photoconductance due to the pure anatase phase of the TiO2. The large surface area and one-dimensional nanostructure of the TiO2 nanotubes lead to great photosensitivity (more than 4 orders of magnitude) and fast response with rise time and decay time of 0.5 and 0.7 s, respectively. High responsivity of 13 A/W is found under 1.06 mW/cm(2) UV (lambda = 312 nm) illumination at 2.5 V bias, which is much higher than those of commercial UV photodetectors. The high responsivity mainly comes from the internal gain induced by the desorption of oxygen from the nanotube surfaces and the reduction of the Schottky barrier at TiO2/Ag contact under UV illumination. The devices are promising for large-area UV photodetctor applications.