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Efficient phonon cascades in hot photoluminescence of WSe$_2$ monolayers
- Source :
- Nature Communications, volume 12, Article number: 538 (2021)
- Publication Year :
- 2020
-
Abstract
- 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.<br />Comment: 13 pages, 10 figures
Details
- Database :
- arXiv
- Journal :
- Nature Communications, volume 12, Article number: 538 (2021)
- Publication Type :
- Report
- Accession number :
- edsarx.2007.05369
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1038/s41467-020-20244-7