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Research Highlight

Giant Enhancement of Exciton Diffusivity in Two-Dimensional Semiconductors

Giant Enhancement of Exciton Diffusivity in Two-Dimensional Semiconductors
(A) Intensity dependence of photoluminescence (PL) from suspended monolayer MoS2 as seen through the optical microscope (false color) reveals spatial broadening compared to laser spot. (B) Normalized and unnormalized PL emission profiles from (A) reveal in (C) a sharp laser intensity onset in spatial broadening, indicating an exciton Mott transition due to formation of an electron hole plasma. Bottom: Schematic shows how trapped charges generated by the plasma mediate scattering of excitons for more than a 10X enhancement in exciton diffusivity.

Scientific Achievement

Photogenerated charges, trapped at defects in 2D MoS2 monolayer crystals, were shown to mediate the scattering of excitons for a giant enhancement of exciton diffusivity from 1.5 to 22.5 cm2/s.

Significance and Impact

Understanding how to improve and control exciton transport in 2D semiconductors opens new avenues for the development of high-performance excitonic  devices, energy conversion, and photodetectors. 

Research Details

The spatial expansion and intensity of photoluminescence from suspended ML MoS2 crystals were measured at 298K vs. cw 532 nm-laser power, revealing an exciton Mott transition due to electron hole plasma formation. 

Ultrafast pump-probe differential reflectance and spectroscopy measurements revealed that exciton dynamics were preserved, despite the higher diffusivity.

 

Y. Yu, Y. Yu, G. Li, A. A. Puretzky, D. B. Geohegan, and L. Cao, "Giant Enhancement of Exciton Diffusivity in Two-Dimensional Semiconductors," Sci. Adv. 6 (51) eabb4823 (2020).   DOI: 10.1126/sciadv.abb4823