Highly intrinsic carrier mobility in tin diselenide crystal accessed with ultrafast terahertz spectroscopy

Tin diselenide (SnSe₂), a layered transition metal dichalcogenide (TMDC), stands out among other TMDCs for its extraordinary photoactive ability and low thermal conductivity. Consequently, it has stimulated many influential researches on photodetectors, ultrafast pulse shaping, thermoelectric devices, etc. However, the carrier mobility in SnSe₂, as determined experimentally, remains limited to tens of cm²V^-1s^-1. This limitation poses a challenge for achieving high-performance SnSe₂-based devices. Theoretical calculations, on the other hand, predict that the carrier mobility in SnSe₂ can reach hundreds of cm²V^-1s^-1, approximately one order of magnitude higher than experimental value. Interestingly, the carrier mobility could be underestimated significantly in long-range transportation measurements due to the presence of defects and boundary scattering effects. To address this discrepancy, we employ optic pump terahertz probe spectroscopy to access the photoinduced dynamical THz photoconductivity of SnSe₂. Our findings reveal that the intrinsic carrier mobility in conventional SnSe₂ single crystal is remarkably high, reaching 353.2 ± 37.7 cm²V^-1s^-1, consistent with the theoretical prediction. Additionally, dynamical THz photoconductivity measurements reveal that the SnSe₂ crystal containing rich defects efficiently capture photoinduced conduction-band electrons and valence-band holes with time constants of ∼20 and ∼200 ps, respectively. Meanwhile, we observe an impulsively stimulated Raman scattering at 0.60 THz. Our study not only demonstrates ultrafast THz spectroscopy as a reliable method for determining intrinsic carrier mobility and detection of low frequency coherent Raman mode in materials but also provides valuable reference for the future application of high-performance SnSe₂-based devices.