Effects of surface self-assembled NH4+ on the performance of TiO2-based ultraviolet photodetectors

In this letter, a metal–semiconductor–metal ultraviolet photodetector based on NH4+ modified TiO2 film was fabricated. The barrier height between TiO2 and Au electrode was lowered due to the self-assembled NH4+ on TiO2 surface, leading to a significant improvement in the device performance. At 5 V bias, a photocurrent of 84.93 μA and a responsivity of 361.07 A/W were obtained under the irradiation of 300 nm UV light. The dark current was merely 88.8 pA, two orders of magnitude lower than that of the TiO2 device (2.85 nA). The rise time was sharply shortened from 2.735 s to 366.9 ms. The ratio of photocurrent to dark current was nearly 6 orders of magnitude.