期刊
ADVANCED SCIENCE
卷 9, 期 10, 页码 -出版社
WILEY
DOI: 10.1002/advs.202105746
关键词
exciton diffusion; heat conduction; hot-carrier expansion; transient absorption microscopy; tungsten disulfide
资金
- National Natural Science Foundation of China [62075240, 62105364]
- Science Fund for Distinguished Young Scholars of Hunan Province [2020JJ2036]
- Science and Technology Innovation Program of Hunan Province [2021RC2068]
The excited-state dynamics in layered tungsten disulfide (WS2) were studied using transient absorption microscopy, which revealed the ultrafast hot carrier expansion and its potential in improving carrier harvesting. A cascaded transport model was proposed to explain the carrier diffusion mechanism in this system.
The competition between different spatiotemporal carrier relaxation determines the carrier harvesting in optoelectronic semiconductors, which can be greatly optimized by utilizing the ultrafast spatial expansion of highly energetic carriers before their energy dissipation via carrier-phonon interactions. Here, the excited-state dynamics in layered tungsten disulfide (WS2) are primarily imaged in the temporal, spatial, and spectral domains by transient absorption microscopy. Ultrafast hot carrier expansion is captured in the first 1.4 ps immediately after photoexcitation, with a mean diffusivity up to 980 cm(2) s(-1). This carrier diffusivity then rapidly weakens, reaching a conventional linear spread of 10.5 cm(2) s(-1) after 2 ps after the hot carriers cool down to the band edge and form bound excitons. The novel carrier diffusion can be well characterized by a cascaded transport model including 3D thermal transport and thermo-optical conversion, in which the carrier temperature gradient and lattice thermal transport govern the initial hot carrier expansion and long-term exciton diffusion rates, respectively. The ultrafast hot carrier expansion breaks the limit of slow exciton diffusion in 2D transition metal dichalcogenides, providing potential guidance for high-performance applications and thermal management of optoelectronic technology.
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