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Excitonic Transport and Intervalley Scattering Dynamics in Large‐Size Exfoliated MoSe 2 Monolayer Investigated by Heterodyned Transient Grating Spectroscopy
Author(s) -
Kuhn Henning,
Wagner Julian,
Han Shuangping,
Bernhardt Robin,
Gao Yan,
Xiao Liantuan,
Zhu Jingyi,
Loosdrecht Paul H. M.
Publication year - 2020
Publication title -
laser and photonics reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.778
H-Index - 116
eISSN - 1863-8899
pISSN - 1863-8880
DOI - 10.1002/lpor.202000029
Subject(s) - exciton , annihilation , monolayer , scattering , condensed matter physics , photoluminescence , population , materials science , spectroscopy , grating , molecular physics , physics , optics , optoelectronics , nanotechnology , quantum mechanics , demography , sociology
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 MoSe 2 are addressed directly using heterodyned transient grating spectroscopy at room temperature. While the free exciton population is found to be long‐lived (≈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 ≈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 ≈ 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.