Ultrafast Dynamics of Defect-Assisted Electron–Hole
Recombination in Monolayer MoS<sub>2</sub>
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Abstract
In
this Letter, we present nondegenerate ultrafast optical pump–probe
studies of the carrier recombination dynamics in MoS<sub>2</sub> 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 ∼2 ps and a slow time scale that
lasts longer than ∼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