Low dark current metal-semiconductor-metal ultraviolet photodetectors based on sol-gel-derived TiO_2 films

摘要

The titanium dioxide (TiO_2) films prepared by sol-gel processing were used to fabricate metal-semiconductor-metal ultraviolet photodetectors. A very low dark current of 5.38 pA (current density of 3.84 nA/cm2) at 5 V bias is obtained, which is ascribed to the high effective Schottky barrier between Au and TiO_2 films. The x-ray photoelectron spectroscopy analysis demonstrates that the concentration of oxygen vacancies is very low in the surface of the TiO_2 films, which is responsible for the high effective Schottky barrier. The devices exhibit a cutoff wavelength at about 380 nm and a large UV-to-visible rejection ratio (340 versus 400 nm) of three orders of magnitude. The peak responsivity of the devices is 17.5 AAV at 5 V bias, indicating the presence of internal photoconductive gain induced by desorption of oxygen on the TiO_2 surface.