Ultrafast carrier and phonon dynamics in few-layer 2H-MoTe.

By using femtosecond pump-probe spectroscopy with broadband detection from near-infrared to midinfrared, the carrier and phonon dynamics in few-layer 2H-MoTe after ultrafast excitation have been investigated in detail. Immediately following the photoexcitation, an ultrafast relaxation of the generated hot carriers by releasing phonons is observed within hundreds of femtoseconds. The subsequent electron-hole recombination with a time constant of ∼1.5 ps is clearly identified and demonstrated to be mediated through a defect-assisted process. Furthermore, we confirm that the observed redshift of the exciton resonance energy on longer time scales arises from the ultrafast thermalization of the 2H-MoTe lattice caused by the transfer of electronic excitation to the phonon system. As a result, the thermalization dynamics of the lattice within 2 ps and the following cooling process of the phonon system on the 100 ps time scale are directly monitored.