Revealing a Nonlinear Photocurrent in the Graphene/MoS Heterostructure via Terahertz Emission Spectroscopy.

Heterostructures composed of graphene (Gr) and transition metal dichalcogenides (TMDs) establish a new platform for optoelectronic applications. A substantial amount of research has concentrated on the interfacial charge transfer (CT) within heterostructures, yet investigations into the nonlinear effects occurring within these heterostructures have been relatively scarce. Utilizing terahertz (THz) emission spectroscopy, we demonstrate the synergistic interaction between interfacial CT and nonlinear photocurrent within the Gr/MoS heterostructure. Our study shows that despite the cancellation of photocurrents from CT in the MoS/Gr/MoS sandwich heterostructure, THz emissions are still observable, indicating additional photocurrents from other effects. By conducting experiments that involved varying the pump fluence, sample azimuthal angle, incidence angle, and pump polarization states, we determined that the THz radiation in the MoS/Gr/MoS heterostructure is dominated by the photon drag effect (PDE), particularly dominated by the photon drag injection current. For the case of the Gr/MoS heterostructure, both CT and PDE play a role in THz emission, and the contribution of CT to THz emission is dominant, with an estimated CT:PDE ratio of 5:2. The study provides a foundation for the application of these heterostructures in next-generation optoelectronic devices.