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Substrate-Dependent Exciton Diffusion and Annihilation in Chemically Treated MoS2 and WS2
journal contribution
posted on 2020-05-21, 21:31 authored by A. J. Goodman, D.-H. Lien, G. H. Ahn, L. L. Spiegel, M. Amani, A. P. Willard, A. Javey, W. A. TisdaleAtomically thin semiconductors
such as monolayer MoS2 and WS2 exhibit nonlinear
exciton–exciton annihilation
at notably low excitation densities (below ∼10 excitons/μm2 in exfoliated MoS2). Here, we show that the density
threshold at which annihilation occurs can be tuned by changing the
underlying substrate. When the supporting substrate is changed from
SiO2 to Al2O3 or SrTiO3, the rate constant for second-order exciton–exciton annihilation, kXX [cm2/s], is reduced by 1 or 2
orders of magnitude, respectively. Using transient photoluminescence
microscopy, we measure the effective room-temperature exciton diffusion
coefficient in bis(trifluoromethane)sulfonimide-treated MoS2 to be in the range D = 0.03–0.06 cm2/s, corresponding to a diffusion length of LD = 350 nm for an exciton lifetime of τ = 18 ns,
which does not depend strongly on the substrate. We discuss possible
mechanisms for the observed behavior, including substrate permittivity,
long-range exciton–exciton or exciton–charge interactions,
defect-mediated Auger recombination, and spatially inhomogeneous exciton
populations arising from substrate-induced disorder. Exciton annihilation
limits the overall efficiency of 2D semiconductor devices operating
at high exciton densities; the ability to tune these interactions
via the underlying substrate is an important step toward more efficient
optoelectronic technologies featuring atomically thin materials.
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L Dmonolayer MoS 2excitation densitiesdefect-mediated Auger recombinationexciton lifetimeWS 2 Atomicallyphotoluminescence microscopyrange Dexciton densitiessubstrate-induced disorderAl 2 O 32 ordersExciton annihilation limits18 nsChemically Treated MoS 2350 nmroom-temperature exciton diffusion coefficientdensity thresholddiffusion lengthoptoelectronic technologiesk XXexciton populationsSubstrate-Dependent Exciton Diffusion2 D semiconductor devicesexfoliated MoS 2substrate permittivitySrTiO 3SiO 2
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