Interplay between Ultrafast Shift Current and Ultrafast Photon Drag Current in Tellurium Nanotubes

Photocurrent induced by nonlinear optical effects has innovated fundamental optic physics in optoelectronic devices, including nonlinear photodetectors, nonlinear optical absorbers, and solar cells. The cooperative interaction between different kinds of nonlinear photocurrents would be a complex yet interesting issue. Herein, we have prepared tellurium (Te) nanotube films to study the transient nonlinear photocurrent utilizing terahertz (THz) emission spectroscopy excited by a femtosecond pulse laser. The THz wave is generated from the interplay between the ultrafast shift current and ultrafast photon drag current, which are ascribed to the photogalvanic effect (PGE) and photon drag effect (PDE), respectively. According to the THz emission spectroscopy excited from opposite incident planes, the contribution ratio of the PDE and PGE is calculated as 1.2:1 for the THz parallel ETHz-p component and 1:1 for the perpendicular E(THz-s )component under the p-polarized excitation. The different ratios between these two components are related to the different nonlinear susceptibility tensor elements. In particular, the contribution of the PDE and PGE can be dynamically modulated by the polarization angle of the incident laser, which further flexibly modulates both ETHz-p and ETHz-s. As such, the reconstructed THz wave is elliptically polarized with the fixed ellipticity, while the major axis of the ellipse rotates clockwise with different magnitudes. These results highlight the THz emission spectroscopy as an effective tool to clarify the interplay mechanism between different nonlinear photocurrents, which could open a new avenue for ultrafast photovoltaic applications.