Femtosecond dynamics of exciton and coherent lattice vibrations in van der Waals Layered Materials
Ji-Hee Kim a b
a Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
b Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#Sol2D19. Two Dimensional Layered Semiconductors
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Efrat Lifshitz, Cristiane Morais Smith and Doron Naveh
Poster, Ji-Hee Kim, 364
Publication date: 16th July 2019

Van der Waals (vdW) layered materials have great potential for optoelectronic devices, such as photodetectors, photovoltaics with efficient power conversion, and high-speed memory/switching devices. Reduced dimensionality in the vdW layered materials provides strong Coulomb interaction with a large exciton binding energy of about 0.3~1 eV in a monolayer although these values are scaled down to less than 0.1 eV by charge screening in a thin film.

Here, we will discuss the photoexcited dynamics of free carriers, excitons and coherent lattice vibrations of van der Waals layered materials, such as MoS2, WSe2 and 2H-MoTe2 by using femtosecond pump-probe spectroscopy. When photoexcited charge carrier density in the vdW layered material is sufficiently low, exciton-exciton scattering prevails over exciton-phonon scattering due to the strong Coulomb coupling, resulting in huge enhancement of quantum yield of photoexcited carriers [3]. When the carrier density is over 1014 cm-2 per monolayer, the structural deformation occurs, and this phase transition is fully reversible within a picosecond via light control.

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