Visualizing Hot‐Carrier Expansion and Cascaded Transport in WS2 by Ultrafast Transient Absorption Microscopy. Issue 10 (1st February 2022)

• Record Type: Journal Article
• Authors: Liu, Qirui; Wei, Ke; Tang, Yuxiang; Xu, Zhongjie; Cheng, Xiang'ai; Jiang, Tian
• Is Part Of: Advanced science. Volume 9:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-01
• Subjects: exciton diffusion -- heat conduction -- hot‐carrier expansion -- transient absorption microscopy -- tungsten disulfide; Science -- Periodicals; 505
• DOI: 10.1002/advs.202105746
• Languages: English
• ISSNs: 2198-3844

Abstract

Abstract: 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. Abstract : A novel spatiotemporal photoexcitation which includes a cascaded process of hot‐carrier expansion, negative contraction, and exciton diffusion is studied in 2D WS2, determining an initial average diffusivity of nearly 10 3 cm 2 s −1 that is 10 2 times higher than the followed excitonic. This discovery has great potential for improving the efficiency and thermal management of transition metal dichalcogenides‐based optoelectronic devices.