Fig. 3: Ultrafast response of the spontaneous photovoltaic effect in the MoSSe devices.

a Schematic of the ultrafast time-resolved photocurrent measurement. The two ultrafast pulses with a time delay Δt are focused collinearly on the device. The generated photocurrent is measured by a lock-in amplifier. b Autocorrelation photocurrent of the device as a function of the time delay between the two pulses at zero bias voltage, with increasing excitation power from bottom to the top. The circles are the experimental data, and the solid lines are the exponential fits. The inset black curves at the top represent the pump and probe pulses, and the black arrow denotes the time delay. c Response time constant of the MoSSe-based device at different incident power, which is extracted from the exponential fitting of the photocurrent-delay curves in (b). Here, the error bars show the standard errors of the fitting parameters.