Phonon-assisted hot carrier re-population in 2D Te thin films

Two-dimensional (2D) Tellurium (Te) films, emerging as a new member of a single elemental material, have gained significant attention for its potential in advanced optoelectronic devices. Here, we examined the hot carrier dynamics of Te via ultrafast transient reflection spectroscopy. The hot carrier population and relaxation processes in the second excited state are studied under resonant (1.55 eV) and nonresonant (3.1 eV) excitation conditions. A notably prolonged carrier relaxation time of 219 ps was observed under resonant excitation conditions. In contrast, hot carrier relaxation under nonresonant excitation showed an abnormal trend of rapid decrease followed by an abrupt increase around a time delay of 20 ps. This anomaly is attributed to the re-population of hot carriers, driven by decreased thermalization rates coupled with a retardation of carrier intervalley scattering within Te. We also found that the strong electron-phonon coupling in Te films promoted intervalley scattering. These results provide fundamental insights into the excited-state relaxation processes in Te, offering potential opportunities for the advancement of high-efficiency Te-based thermoelectric and electric devices.