Exciton and trion dynamics in atomically thin MoSe2 and WSe2: effect of localization

Abstract

We present a detailed investigation of the exciton and trion dynamics in naturally doped MoSe2 and WSe2 single atomic layers as a function of temperature in the range 10-300K under above band-gap laser excitation. By combining time-integrated and time-resolved photoluminescence (PL) spectroscopy we show the importance of exciton and trion localization in both materials at low temperatures. We also reveal the transition to delocalized exciton complexes at higher temperatures where the exciton and trion thermal energy exceeds the typical localization energy. This is accompanied with strong changes in PL including suppression of the trion PL and decrease of the trion PL life-time, as well as significant changes for neutral excitons in the temperature dependence of the PL intensity and appearance of a pronounced slow PL decay component. In MoSe2 and WSe2 studied here, the temperatures where such strong changes occur are observed at around 100 and 200 K, respectively, in agreement with their inhomogeneous PL linewidth of 8 and 20 meV at T~10K. The observed behavior is a result of a complex interplay between influences of the specific energy ordering of bright and dark excitons in MoSe2 and WSe2, sample doping, trion and exciton localization and various temperature-dependent non-radiative processes.

References in corpus (9)

• Light-emitting diodes by bandstructure engineering in van der Waals heterostructures
• Tightly bound excitons in monolayer WSe2
• Probing Excitonic Dark States in Single-layer Tungsten Disulfide
• Magnetic Control of Valley Pseudospin in Monolayer WSe2
• Valley Zeeman Effect in Elementary Optical Excitations of a Monolayer WSe2
• Valley Splitting and Polarization by the Zeeman Effect in Monolayer MoSe2
• Nonlinear Photoluminescence in Atomically Thin Layered WSe2 Arising from Diffusion-Assisted Exciton-Exciton Annihilation
• Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
• Magneto-optics in transition metal diselenide monolayers

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• Exciton optics, dynamics and transport in atomically thin semiconductors
• Phonon-assisted exciton and trion conversion efficiency in transition metal Dichalcogenides
• Inter-layer charge transport controlled by exciton-trion coherent coupling
• Valley Dynamics of Excitons in Monolayer Dichalcogenides
• Long-lived spin polarization in n-doped MoSe${}_2$ monolayers
• Excitonic theory of doping-dependent optical response in atomically thin semiconductors
• Nonexponential photoluminescence dynamics in an inhomogeneous ensemble of excitons in WSe${}_2$ monolayers
• Signatures of defect-localized charged excitons in the photoluminescence of monolayer molybdenum disulfide
• Heteroepitaxial growth of high optical quality, wafer-scale van der Waals heterostrucutres