Posted October 26, 2016 by Rino Rakhmata Mukti, Dr. rer.nat in Guest Seminar

Atomically-thin Layered Semiconductors for Novel Photonics

Dr. Goki Eda, National University of Singapore, 26 October 2016, 13.00-14.00

Department of Physics/Chemistry, National University of Singapore
Centre for Advanced 2D Materials and Graphene Research Centre

Two-dimensional (2D) semiconductors such as atomically thin layers of MoS2 and phosphorene
are emerging as building blocks for novel photonic devices. Despite being only a few atoms thick,
they exhibit unusually strong light-matter coupling mediated by strongly bound excitons, which are
elementary excitation of solids consisting of electron-hole pairs held together by Coulomb forces.
Unlike in conventional quantum wells, excitonic effects dominate optical transitions in 2D
semiconductors even at room temperature and allow their exploitation for device applications. Recent
rapid progresses in both materials synthesis and device demonstrations highlight the potential of 2D
semiconductors for ultra-fast photo-detectors, flexible photovoltaic devices, chiral light emitters,
single photon sources, and ultra-low threshold lasers. On the other hand, many basic electronic and
excitonic properties of 2D semiconductors and their heterostructures remain elusive. In this talk, I will
start by introducing some basic materials properties of 2D semiconductors from the transition metal
dichalcogenide (TMD) family with a focus on electronic structure evolution and unique polymorphism
[1]. Then I will discuss our recent experimental investigation into exciton dynamics in monolayer
TMDs and their heterostructure from the viewpoint of their potential photonics applications. I will
touch upon giant optical absorption arising from band nesting effects [2], ultrafast charge and energy
transfer in hetero-bilayers [3], and peculiar optical response arising from exciton-plasmon coupling in
monolayer TMDs hybridized with Ag nanoparticles [4].
[1] M. Chhowalla et al. “The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets”
Nature Chem. 5, 263 (2013).
[2] D. Kozawa et al. “Photocarrier relaxation pathway in two-dimensional semiconducting transition metal
dichalcogenides” Nature Comm. 5, 4543 (2014)
[3] D. Kozawa et al. “Evidence for fast energy transfer in MoSe2/WS2 heterostructures” Nano Lett., 16, 4087
[4] W. Zhao et. al. “Exciton-plasmon coupling and electromagnetically induced transparency in monolayer
semiconductors hybridized with Ag nanoparticles” Adv. Mater. 28, 2709 (2016).

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