Distance dependence of the energy transfer mechanism in WS${}_2$-graphene heterostructures

Abstract

We report on the mechanism of energy transfer in van der Waals heterostructures of the two-dimensional semiconductor WS${}_2$ and graphene with varying interlayer distances, achieved through spacer layers of hexagonal boron nitride (hBN). We record photoluminescence and reflection spectra at interlayer distances between 0.5 nm and 5.8 nm (0-16 hBN layers). We find that the energy transfer is dominated by states outside the light cone, indicative of a Förster transfer process, with an additional contribution from a Dexter process at 0.5 nm interlayer distance. We find that the measured dependence of the luminescence intensity on interlayer distances above 1 nm can be quantitatively described using recently reported values of the Förster transfer rates of thermalized charge carriers. At smaller interlayer distances, the experimentally observed transfer rates exceed the predictions and furthermore depend on excess energy as well as on excitation density. Since the transfer probability of the Förster mechanism depends on the momentum of electron-hole pairs, we conclude that at these distances, the transfer is driven by non-thermalized charge carrier distributions.

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Cited by in corpus (4)

• Benchmarking the integration of hexagonal boron nitride crystals and thin films into graphene-based van der Waals heterostructures
• Current-induced brightening of vacancy-related emitters in hexagonal boron nitride
• Fast Interlayer Energy Transfer from the Lower Bandgap MoS2 to the Higher Bandgap WS2
• Graphene as a Tunable Nonradiative Bath for Moiré Excitons