Ultrafast photovoltage microscopy on Sb-doped Bi₂Se₃ nanoplates

Antimony-doped Bi₂Se₃ displays prominent carrier transport that covers hundreds of micrometers, which enables efficient photocurrent generation far from the collecting electrodes even above 100K. To uncover the mechanism driving this behavior, this study employs Ultrafast Photovoltage Microscopy (UPVM) to further investigate the dynamics of excited states in Bi_2-xSb_xSe₃ nanoplates with subpicosecond resolution. The pump pulse-induced photovoltage suppression recovers within 50 ps to 1 ns as the pump fluence increases, revealing an anomalously high carrier diffusivity that decreases with increasing carrier concentration. Additionally, different methods were employed to extract the diffusivity in this material, resulting in two contrasting values of 2,000cm²/s and 500 cm²/s. The nature of the super-diffusion could be a hint of excitonic transport that gives rise to the distinctive non-local photocurrent.