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Photodoping as a nonvolatile and reversible method can be used to modify the carrier distribution at the heterojunction interface. Herein, we explore the 2D/3D van der Waals (vdW) graphene/silicon (G/Si) heterostructure in real time by terahertz (THz) emission spectroscopy. Photoinduced doping is introduced by a continuous wave laser, which leads to a screening effect to the built-in electric field at the interface. The resulting decrease in transient photocurrent reduces the THz emission amplitude from the G/Si heterostructure. The photoinduced doping effect suggests a 40% THz intrinsic modulation depth at external reverse bias. This work provides an effective way to actively control the THz emission process from the G/Si interface and paves the way for analyzing the interfacial process under photoinduced doping in vdW heterostructures.

We investigated the terahertz (THz) radiation mechanism of the layered tin sulfide (SnS2) crystal via THz emission spectroscopy. Under non-resonant excitation, THz generation from SnS2 is mainly due to the optical rectification effect, which is verified by the azimuthal angle, polarization angle, and pump fluence dependence of the THz signals. Further incident angle dependent THz signals suggest that the optical progress happened at the surface of SnS2 with both in-plane and out-of-plane photon-induced dipoles. This work puts forward THz emission spectroscopy as a noninvasive characterization tool for the in-plane and out-of-plane photon-induced dipoles in layered materials.