Journal
LASER & PHOTONICS REVIEWS
Volume 14, Issue 12, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/lpor.202000029
Keywords
diffusion transport; exciton annihilation; heterodyned transient grating; intervalley scattering; monolayer MoSe2
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Funding
- DFG (German Research Foundation) [277146847-CRC1238]
- National Natural Science Foundation of China (NSFC) [61605104]
- Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi [201802008]
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Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides are central to the functionality of devices based on them. Here, these properties in a large-size exfoliated high-quality monolayer MoSe2 are addressed directly using heterodyned transient grating spectroscopy at room temperature. While the free exciton population is found to be long-lived (approximate to 230 ps), an extremely fast intervalley scattering (<= 170 fs) is observed, leading to a negligible valley polarization, consistent with steady state photoluminescence measurements and theoretical calculation. The exciton population decay shows an appreciable contribution from the exciton-exciton annihilation, with an annihilation rate of approximate to 0.01 cm(2) s(-1). The annihilation process also leads to a significant distortion of the transient grating evolution. Taking this distortion into account, consistent exciton diffusion constants D approximate to 1.4 cm(2) s(-1) are found by a model simulation in the excitation density range of 10(11)-10(12) cm(-2). The presented results highlight the importance of correctly considering the many-body annihilation processes to obtain a pronounced understanding of the excitonic properties of monolayer transition metal dichalcogenides.
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