Probing Interlayer Interactions in Transition Metal Dichalcogenide Heterostructures by Optical Spectroscopy: MoS<sub>2</sub>/WS<sub>2</sub> and MoSe<sub>2</sub>/WSe<sub>2</sub>

Abstract

We have applied optical absorption spectroscopy to investigate van der Waals heterostructures formed of pairs of monolayer transition metal dichalcogenide crystals, choosing MoS<sub>2</sub>/WS<sub>2</sub> and MoSe<sub>2</sub>/WSe<sub>2</sub> as test cases. In the heterostructure spectra, we observe a significant broadening of the excitonic transitions compared to the corresponding features in the isolated layers. The broadening is interpreted as a lifetime effect arising from decay of excitons initially created in either layer through charge transfer processes expected for a staggered band alignment. The measured spectral broadening of 20 meV – 35 meV implies lifetimes for charge separation of the near band-edge A and B excitons in the range of 20–35 fs. Higher-lying transitions exhibit still greater broadening

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