Ultrafast Dynamics of Defect-Assisted Electron-Hole Recombination in Monolayer MoS2

Abstract

In this letter, we present non-degenerate ultrafast optical pump-probe studies of the carrier recombination dynamics in MoS${}_2$ monolayers. By tuning the probe to wavelengths much longer than the exciton line, we make the probe transmission sensitive to the total population of photoexcited electrons and holes. Our measurement reveals two distinct time scales over which the photoexcited electrons and holes recombine; a fast time scale that lasts $\sim$2 ps and a slow time scale that lasts longer than $\sim$100 ps. The temperature and the pump fluence dependence of the observed carrier dynamics are consistent with defect-assisted recombination as being the dominant mechanism for electron-hole recombination in which the electrons and holes are captured by defects via Auger processes. Strong Coulomb interactions in two dimensional atomic materials, together with strong electron and hole correlations in two dimensional metal dichalcogenides, make Auger processes particularly effective for carrier capture by defects. We present a model for carrier recombination dynamics that quantitatively explains all features of our data for different temperatures and pump fluences. The theoretical estimates for the rate constants for Auger carrier capture are in good agreement with the experimentally determined values. Our results underscore the important role played by Auger processes in two dimensional atomic materials.

25 pages, 10 figures

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• Two-dimensional transition metal dichalcogenides under electron irradiation: defect production and doping
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• First-principles approach to excitons in time-resolved and angle-resolved photoemission spectra
• Dark excitons and the elusive valley polarization in transition metal dichalcogenides
• Ultra-low power threshold for laser induced changes in optical properties of 2D Molybdenum dichalcogenides
• Optically Driven Magnetic Phase Transition of Monolayer RuCl3
• Observation of intervalley biexcitonic optical Stark effect in monolayer WS2
• Observation of exciton-exciton interaction mediated valley depolarization in monolayer MoSe${}_2$
• Carrier Trapping by Oxygen Impurities in Molybdenum Diselenide
• Auger recombination of dark excitons in $\mathrm{W}{\mathrm{S}}_2$ and $\mathrm{WS}{\mathrm{e}}_2$ monolayers
• Electron-phonon interaction, excitations and ultrafast photoemission from doped monolayer MoS2
• Mid-Infrared Ultrafast Carrier Dynamics in Thin Film Black Phosphorus
• Two-dimensional Ga${}_2$O${}_3$ glass: a large scale passivation and protection material for monolayer WS${}_2$