Long-Lived Charge Separation Following Pump-Energy Dependent Ultrafast Charge Transfer in Graphene/WS${}_2$ Heterostructures

Abstract

Van der Waals heterostructures consisting of graphene and transition metal dichalcogenides (TMDCs) have recently shown great promise for high-performance optoelectronic applications. However, an in-depth understanding of the critical processes for device operation, namely interfacial charge transfer (CT) and recombination, has so far remained elusive. Here, we investigate these processes in graphene-WS${}_2$ heterostructures, by complementarily probing the ultrafast terahertz photoconductivity in graphene and the transient absorption dynamics in WS${}_2$ following photoexcitation. We find that CT across graphene-WS${}_2$ interfaces occurs via photo-thermionic emission for sub-A-exciton excitation, and direct hole transfer from WS${}_2$ to the valence band of graphene for above-A-exciton excitation. Remarkably, we observe that separated charges in the heterostructure following CT live extremely long: beyond 1 ns, in contrast to ~1 ps charge separation reported in previous studies. This leads to efficient photogating of graphene. These findings provide relevant insights to optimize further the performance of optoelectronic devices, in particular photodetection.

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• Sub-ps thermionic electron injection effects on exciton-formation dynamics at a van der Waals semiconductor/metal interface
• Interfacial Charge Transfer and Ultrafast Photonics Application of 2D Graphene/InSe Heterostructure
• Reduced absorption due to defect-localized interlayer excitons in transition metal dichalcogenide-graphene heterostructures
• Charge quenching at defect states in transition metal dichalcogenide-graphene van der Waals heterobilayers
• Light-matter interactions in layered materials and heterostructures: from moiré physics and magneto-optical effects to ultrafast dynamics and hybrid meta-photonics
• Designable exciton mixing through layer alignment in WS${}_2$-graphene heterostructures
• Ultrafast electronic heat dissipation through surface-to-bulk Coulomb coupling in quantum materials