Probing momentum-indirect excitons by near-resonance photoluminescence excitation spectroscopy in WS2 monolayer
Open Access
- 1 July 2020
- journal article
- research article
- Published by IOP Publishing in 2D Materials
- Vol. 7 (3), 031002
- https://doi.org/10.1088/2053-1583/ab817a
Abstract
Coulomb-bound electron-hole pairs (excitons) dominate the optical response of atomically-thin transition metal dichalcogenides (TMDs) semiconductors. The photoluminescence spectrum in W-based TMDs monolayers (i.e. WS2 and WSe2) at low temperature exhibits much richer features than Mo-based TMDs monolayers, whose origin is currently not well understood. Herein, by using near-resonant photoluminescence excitation spectroscopy, we probe the scattering events between excitons and phonons with large (k) over cap -momentum, which provides strong evidence for the momentum-indirect nature of the optical bandgap in monolayer WS2. The scattering between carriers and zone-edge phonons creates excitons at different valleys, among which, the lowest-energy is momentum-indirect. Our findings highlight that more efforts are required to solve the current debate on the inherent bandgap nature of TMD monolayers and the complex photoluminescence spectrum reported on W-based compounds.Funding Information
- National Research Foundation Singapore (NRF2017-NRF-ANR005 2D CHIRAL)
- Singapore Ministry of Education (MOE2017-T2-1-040)
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