Exciton‐Exciton Annihilation Dynamics: Excitonic Transport and Intervalley Scattering Dynamics in Large‐Size Exfoliated MoSe₂ Monolayer Investigated by Heterodyned Transient Grating Spectroscopy (Laser Photonics Rev. 14(12)/2020)

Abstract

Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides (TMDCs) are central to the functionality of devices based on them. In article number 2000029 by Jingyi Zhu, Paul H. M. van Loosdrecht, and co‐workers investigate exciton‐exciton annihilation dynamics and its effect in the distortion of the diffusion grating in an exfoliated monolayer TMDC, MoSe2.

Bright and Efficient Light‐Emitting Devices Based on 2D Transition Metal Dichalcogenides

“…[61,144,173] At higher generation rates, the PL QY of MoS 2 (and other TMDCs) drops as recombination at high exciton densities is dominated by the annihilation of two adjacent excitons, a process so-called exciton-exciton annihilation (EEA). [99,[217][218][219][220] EEA is a process in which neutral excitons recombine nonradiatively in the course of colliding with other excitons, causing a reduction in the luminescent efficiency of the material at higher generation rates. [99,[217][218][219][220] To eliminate the efficiency droop in 2D semiconductors, a detailed investigation on the origin of the EEA process is required.…”

“…[99,[217][218][219][220] EEA is a process in which neutral excitons recombine nonradiatively in the course of colliding with other excitons, causing a reduction in the luminescent efficiency of the material at higher generation rates. [99,[217][218][219][220] To eliminate the efficiency droop in 2D semiconductors, a detailed investigation on the origin of the EEA process is required. It is found that the lifetime of excitons is inversely related to the EEA coefficient (C EAA ), a parameter that measures the rate of annihilation.…”

Spatiotemporal Microscopy: Shining Light on Transport Phenomena

“…Transient grating based approaches have been extensively used for the measurement of the diffusion properties of charge carriers. Among the successful examples are applications to studying exciton diffusion [ 16 ] and, more recently, 2D materials such as WSe 2 [ 25 ] and MoSe 2 [ 26 ] monolayers. Another example are ambipolar mobilities, e.g., the combined electron and hole mobility, in semiconductors [ 27–29 ] including the recent observation of high ambipolar mobility and ultra‐high thermal conductivity in cubic boron arsenide [ 30 ] by the Chen group, a finding that was in parallel reported by Yue et al., using widefield imaging‐based transient reflection SPTM: [ 31 ] This is a great example of how compatible information can be obtained using different SPTM techniques.…”

“…More recently, the same approach was used to study rapid valley depolarization in 2D materials, occurring within 170 femtoseconds for MoSe 2 . [ 26,34 ]…”