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Study of the optoelectronic properties of atomically thin WSe2

Abstract : Transition Metal Dichalcogenides (TMDs) are a family of layered materials with potential applications in optics and electronics. Following the discovery of graphene, TMDs were characterized and extraordinary physical properties were discovered: when thinned down to a monolayer, TMDs become direct band gap materials, therefore strongly facilitating light emission. The direct bandgap of these semiconductors is situated on the edge of the Brillouin zone, at the K-point. This is different from standard semiconductors for optoelectronics like GaAs where the bandgap is in the centre of the Brillouin zone. The optical properties are dominated by excitons, and light-matter interaction is extremely strong with up to 20% of light absorption per monolayer. In addition to a bandgap, TMDs present strong spin-orbit coupling and broken inversion symmetry. As a result, the optical transitions across the bandgap have chiral selection rules. The spin states in the valence and conduction bands are well separated in energy by the spin-orbit interaction. This makes it possible to optically address specific spin and valley states in momentum space and monitor their dynamics. As a result monolayer TMDs are exciting model systems for spin and valley physics: these research fields are termed spintronics and valleytronics. This motivated our work on the exact understanding of the optical transitions, their polarization selections rules and the different exciton states.
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Marco Manca. Study of the optoelectronic properties of atomically thin WSe2. Physics [physics]. INSA de Toulouse, 2019. English. ⟨NNT : 2019ISAT0030⟩. ⟨tel-02879948⟩

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