Efficient phonon cascades in WSe<sub>2</sub> monolayers.
MetadataShow full item record
Paradisanos, I., Wang, G., Alexeev, E., Cadore, A., Marie, X., Ferrari, A., Glazov, M. M., & et al. (2021). Efficient phonon cascades in WSe<sub>2</sub> monolayers.. Nature communications, 12 (1), 538. https://doi.org/10.1038/s41467-020-20244-7
Energy relaxation of photo-excited charge carriers is of significant fundamental interest and crucial for the performance of monolayer (1L) transition metal dichaclogenides (TMDs) in optoelectronics. We measure light scattering and emission in 1L-WSe$_2$ close to the laser excitation energy (down to~$\sim$0.6meV). We detect a series of periodic maxima in the hot photoluminescence intensity, stemming from energy states higher than the A-exciton state, in addition to sharp, non-periodic Raman lines related to the phonon modes. We find a period $\sim$15meV for peaks both below (Stokes) and above (anti-Stokes) the laser excitation energy. We detect 7 maxima from 78K to room temperature in the Stokes signal and 5 in the anti-Stokes, of increasing intensity with temperature. We assign these to phonon cascades, whereby carriers undergo phonon-induced transitions between real states in the free-carrier gap with a probability of radiative recombination at each step. We infer that intermediate states in the conduction band at the $\Lambda$-valley of the Brillouin zone participate in the cascade process of 1L-WSe$_2$. The observations explain the primary stages of carrier relaxation, not accessible so far in time-resolved experiments. This is important for optoelectronic applications, such as photodetectors and lasers, because these determine the recovery rate and, as a consequence, the devices' speed and efficiency.
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (696656)
EPSRC (via University of Manchester) (R119256)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (785219)
European Commission Horizon 2020 (H2020) ERC (842251)
EC FP7 ERC (319277)
Embargo Lift Date
External DOI: https://doi.org/10.1038/s41467-020-20244-7
This record's URL: https://www.repository.cam.ac.uk/handle/1810/313041
All rights reserved