A voltage driven dual-mode MoSe2 photodetector with graphene as van der Waals contact

Abstract Two-dimensional (2D) molybdenum selenide (MoSe2) is promising for developing photodetectors for harvesting lights from UV to near infrared band, while high responsivity and fast response speed are difficult to be simultaneously realized. Herein, we present a dual-mode MoSe2 photodetector with asymmetric electrodes, in which Graphene and Cr metal are utilized as Ohmic and Schottky contacts, respectively. The photodiode possesses a fabulous Schottky characteristic with rectification ratio of ~250 and low dark current of ~40 pA at -1 V. Under forward bias voltage of 1 V, the photodetector works at photoconductive mode with slow response speed (decay time: ~5 minutes) but high responsivity (632 mA/W). However, at reverse bias voltage, the photodetector plays as a photovoltaic type device owing to the Schottky barrier between Cr and MoSe2. Because of the reinforced built-in electric field, the photodetector driven at -5 V shows much faster response speeds (rise time: 1.96 ms; decay time: 755 µs). The study provides a deep understanding of an asymmetric structure MoSe2 photodetctors operated at two modes, which promotes a forward step toward 2D material optoelectronics.