Low-Dark-Current TiO2 MSM UV Photodetectors With Pt Schottky Contacts

We report on the fabrication and characterization of very low-dark-current TiO2 metal-semiconductor-metal ultraviolet (UV) photodetectors (PDs) with Pt Schottky contacts. The dark current of the PDs is merely 1.28 pA at a 5-V bias, which is much better than the previously reported data. The photoconductive gain is less than one for a bias of less than 10 V. The remarkable reduction of the dark current and the gain can be attributed to the combined effect of the large Schottky barrier height produced at the Pt/TiO2 contacts and the high quality of the sputtered TiO2 films, such as low intrinsic carrier concentration, large grain size, and absence of oxygen vacancies. The PDs also display a high quantum efficiency and a large UV-to-visible rejection ratio of about three orders of magnitude.