Intrinsic control of interlayer exciton generation rate in van der Waals materials via Janus layers
arXiv:2212.05615 · doi:10.1021/acs.nanolett.2c04724
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@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@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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