Cooling and diffusion characteristics of a hot carrier in the monolayer WS₂

The characteristics of a hot carrier distributed in the C excitonic state of the monolayer WS₂ is investigated by exploiting the transient absorption (TA) spectroscopy. The hot carrier cooling lifetime gradually prolongs from 0.58 ps to 2.68 ps with the absorbed photon flux owing to the hot phonon bottleneck effect, as the excitation photon energy is 2.03 eV. Meanwhile, the normalized TA spectra shows that the spectral feature of hot carriers is different from that of normal carriers. Based on the modified Lennard-Jones model, the average distance among hot carriers can be estimated according to the peak shift of TA spectra and the diffusion velocity can also be calculated simultaneously. The hot carrier limits the diffusion of the photo-generated carrier at the initial several picoseconds. These results help people to elucidate the hot carrier dynamics in 2D TMDCs and give guidance on the designing and optimizing the TMDC-based electronic devices of high performance.