Dispersion of Ultrafast Nonlinear Shift Current in SnTe Revealed by Photon-Energy-Dependent Terahertz Emission Spectroscopy

The dispersion characteristics of nonlinear photocurrent response such as shift current, providing crucial information for understanding the nonlinear optoelectronic properties of semiconductors, yet remains relatively unexplored in a broadband region with non-contact and sensitive experiments. Herein, terahertz (THz) emission spectroscopy is utilized as a wireless and all-optical method to reveal the photon-energy-dependent ultrafast shift current in tin telluride（SnTe ）. The shift current is induced by the bulk photovoltaic effect and further identified by the pump-fluence dependence and light-polarization dependence of THz radiation. Interestingly, the shift-current-dominated THz radiation is enhanced near the bandgap (E_g) and 2E_g excitation due to the resonance in SnTe, and the dispersion of shift current conductivity tensor is unveiled in the energy ranges of 0.5–0.9 eV and 1.2–1.8 eV. This dispersion feature can be well described by the nonlinear anharmonic oscillator model with the high density of states at the resonant positions. These findings provide a fundamental understanding of the dispersion of shift current in experiments and further apply to the development of shift-current based novel THz devices and photovoltaic devices.