We report the optical response of layered bulk and monolayer SnS2 at the surface. The physical mechanism for terahertz (THz) emission in bulk and monolayer SnS2 has been proposed. At 40° incident angle, the drift current accompanied by the surface nonlinear polarization concurrently contribute to THz surface emission in bulk SnS2. The THz radiation in monolayer SnS2 is mainly attributed to the drift photocurrent, which is insensitive to the crystalline symmetry and the pump polarization direction. The corresponding investigation could not only help to clarify the relationship of layer-dependent optical properties, but also make a significant contribution in understanding the nonlinear physical process in other transition metal dichalcogenides (TMDs) materials.
Two-dimensional/ three-dimensional (2D/3D) van der Waals (vdW) heterostructures are one of the most potential candidates for table-top pulse terahertz (THz) emitters. Hence, manipulating carrier information at the interface is important to optimize THz emission performance. Photoinduced doping is an effective way to embellish the carrier characteristic at the interface. Here, we applied the photoinduced doping effect to dynamically manipulate the THz generation process from graphene-silicon (Gr-Si) heterostructure. When photoinduced doping is applied by using 532 nm continuous wave (CW) laser, THz radiation decreases with the increase of CW pump power at the reverse bias. The photoinduced doping attenuates the interfacial built-in electric field, resulting in the decrease of transient photocurrent and further reduction of THz radiation. This photogenerated carrier screening effect has achieved a 95.4% intrinsic THz modulation depth (MD) at the external excitation of 200 mW CW laser under reverse bias voltage -30 V. The intrinsic THz MD is much higher than previous report value due to the optimized heterostructure fabrication and the optimized light spot overlap of CW laser and femtosecond laser. This work proposes a non-destructive and reversible method to actively manipulate the THz emission at the vdW interface and provides an optimized route to realize high intrinsic THz MD in THz region.
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