![]() ![]() Resonances observed in differential conductance (d I/d V) measurements agree with TMD exciton energies despite the fact that the TMD is placed outside the electron tunnelling pathway. We investigate the current-to-voltage ( I− V) characteristics of TMD/graphene/hBN/Au tunnel junctions and compare them with TMD-free reference structures. Our electron transport measurements reveal distinct resonant peaks that coincide in energy with TMD excitons. Here we demonstrate exciton-assisted resonant electron tunnelling in van der Waals tunnel junctions. Furthermore, evidence for defect-assisted resonant tunnelling has been observed in hBN-based junctions 21. Plasmon-assisted resonant tunnelling has been investigated in metallic quantum well structures hosting silver nanorods 19 and graphene-based structures 20. ![]() Similarly, exciton-assisted resonant tunnelling has been observed in conventional semiconductor quantum wells 17, 18. Previous experiments have shown phonon-assisted resonant electron tunnelling in metal–insulator junctions 11, in conventional semiconductor heterostructures 12 and in graphene-based systems 13, 14, 15, 16. In this respect, tunnel junctions with different material combinations form an interesting system for investigating electron tunnelling processes. Tailored heterostructures comprising graphene, hexagonal boron nitride (hBN), TMDs and other 2D materials are currently designed to display properties that are absent in the individual constituents, thus providing a platform for fundamental studies 2, 3, 4, 5, 6, 7 and novel device applications 8, 9, 10. The isolation of two-dimensional (2D) crystals combined with advances in fabrication techniques has enabled the realization of new types of materials, known as van der Waals heterostructures, in which different atomic layers are assembled together in a desired sequence 1. The appearance of such optical modes in electrical transport introduces additional functionality towards van der Waals material–based optoelectronic devices. By placing the TMD outside of the tunnelling pathway, we demonstrate that this tunnelling process does not require any charge injection into the TMD. We study tunnel junctions consisting of graphene and gold electrodes separated by hexagonal boron nitride with an adjacent TMD monolayer and observe prominent resonant features in current-to-voltage measurements appearing at bias voltages that correspond to TMD exciton energies. Here we use a tunnelling process that involves excitons in transition metal dichalcogenides (TMDs). These features can be explained by direct electron–phonon or electron–defect interactions. Signatures of acoustic phonons and defect states have been observed in current-to-voltage measurements. Two-dimensional van der Waals materials are an excellent platform for such studies. ![]() The control of elastic and inelastic electron tunnelling relies on materials with well-defined interfaces. ![]()
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