Excellent Optoelectronic Properties and Low Contact Resistance of Graphene/MoS2 Heterostructure Optoelectronic Devices: First- Principles Calculation and Experimental Verification

Two-dimensional (2D) materials have enormous applications and are widely studied in the field of electronics and optoelectronic devices. The electrical contacts between the 2D materials and the electrodes seriously affect the performance of the 2D material optoelectronic devices. Exploring the electronic structure and transport behavior at the interface between 2D materials and electrodes and the underlying physical causes will contribute to the development of 2D material integrated circuits and optoelectronic fields. In this study, the charge transport barriers at the Au/MoS2 and graphene/MoS2 interfaces were investigated from both the Schottky and tunneling barriers through theoretical calculations, which demonstrated that the graphene/MoS2 interface has not only a very low Schottky barrier but also a low tunneling barrier compared to the Au/MoS2 interface. Then, three types of optoelectronic devices, Au/MoS2/Au, graphene/ MoS2/graphene, and graphene/MoS2/Au field-effect transistors (FETs), were fabricated. Compared with the Au/MoS2/Au device, the graphene/MoS2/graphene device shows an excellent optical response (R = 654 mA W-1 at 532 nm laser with a power density of 4.8 mW cm-2) and ultrafast response time (rise time 9.8 ms, 12.8 ms fall time). The graphene/MoS2/Au device exhibits excellent rectification behavior and optoelectronic response, with almost no current and photocurrent gain and cutoff state under reverse bias, excellent optoelectronic response under positive bias (responsivity R = 293.4 mA W-1 at a power density of 4.8 mW cm-2 for a 532 nm wavelength laser), and excellent response time (rise time 12.55 ms, fall time 15.44 ms). Our studies are expected to bring opportunities for highly sensitive, high-speed, and energy-efficient photodetectors for comprehensive applications.