Engineering the radiative dynamics of thermalized excitons with metal interfaces

Journal Article · 14 February 2022 · New Journal of Physics

DOI: https://doi.org/10.1088/1367-2630/ac4edf · OSTI ID:1848085

Chen, Grace H. ^[1]; Li, David Z. ^[2]; Butcher, Amy ^[1]; High, Alexander A. ^[3]; Chang, Darrick E. ^[4]

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1. Univ. of Chicago, IL (United States)
2. Barcelona Institute of Science and Technology (Spain)
3. Univ. of Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
4. Barcelona Institute of Science and Technology (Spain); Catalan Institution for Research and Advanced Studies (ICREA), Barcleona (Spain)

As a platform for optoelectronic devices based on exciton dynamics, monolayer transition metal dichalcogenides (TMDCs) are often placed near metal interfaces or inside planar cavities. While the radiative properties of point dipoles at metal interfaces has been studied extensively, those of excitons, which are delocalized and exhibit a temperature-dependent momentum distribution, lack a thorough treatment. Here, we analyze the emission properties of excitons in TMDCs near planar metal interfaces and explore their dependence on exciton center-of-mass momentum, transition dipole orientation, and temperature. Defining a characteristic energy scale k_BT_c = ($$\hbar k$$)²/2m (k being the radiative wavevector and m the exciton mass), we find that at temperatures T $$\gg$$ T_c and low densities where the momentum distribution can be characterized by Maxwell-Boltzmann statistics, the modified emission rates (normalized to free space) behave similarly to point dipoles. This similarity in behavior arises due to the broad nature of wavevector components making up the exciton and point dipole emission. On the other hand, the narrow momentum distribution of excitons for T < T_c can result in significantly different emission behavior as compared to point dipoles. These differences can be further amplified by considering excitons with a Bose Einstein distribution at high phase space densities, such as in a condensate phase. We find suppression or enhancement of emission relative to the point dipole case by several orders of magnitude. These insights can help optimize the performance of optoelectronic devices that incorporate 2D semiconductors near metal electrodes and can inform future studies of exciton radiative dynamics at low temperatures. Additionally, these studies show that nanoscale optical cavities are a viable pathway to generating long-lifetime exciton states in TMDCs.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: European Union Horizon 2020; MCIN Plan Nacional Grant; National Science Foundation (NSF)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1848085
• Journal Information: New Journal of Physics, Journal Name: New Journal of Physics Journal Issue: 2 Vol. 24; ISSN 1367-2630
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English