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>
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 β 35 meV implies lifetimes for charge
separation of the near band-edge A and B excitons in the range of
20β35 fs. Higher-lying transitions exhibit still greater broadening