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arXiv · 2212.05615

Intrinsic control of interlayer exciton generation rate in van der Waals materials via Janus layers

Engin Torun·Fulvio Paleari·Milorad V. Milosevic·Ludger Wirtz·Cem Sevik
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Abstract

We demonstrate the possibility of engineering the optical properties of transition metal dichalcogenide heterobilayers when one of the constitutive layers has a Janus structure. This has important consequences for the charge separation efficiency. We investigate different MoS$_2$@Janus layer combinations using first-principles methods including electron-hole interactions (excitons) and exciton-phonon coupling. The direction of the intrinsic electric field from the Janus layer modifies the electronic band alignments and, consequently, the energy separation between interlayer exciton states -- which usually have a very low oscillator strength and hence are almost dark in absorption -- and bright in-plane excitons. We find that in-plane lattice vibrations strongly couple the two states, so that exciton-phonon scattering may be a viable generation mechanism for interlayer excitons upon light absorption. In particular, in the case of MoS$_2$@WSSe, the energy separation of the low-lying interlayer exciton from the in-plane exciton is resonant with the transverse optical phonon modes (40 meV). We thus identify this heterobilayer as a prime candidate for efficient electron-hole pair generation with efficient charge carrier separation.

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Engin Torun, Fulvio Paleari, Milorad V. Milosevic, Ludger Wirtz, Cem Sevik. 2022-12-11. Intrinsic control of interlayer exciton generation rate in van der Waals materials via Janus layers. https://doi.org/10.1021/acs.nanolett.2c04724

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