Lawrence Berkeley National Laboratory

We investigate the interplay between vertical tunneling and lateral transport phenomena in electrically contacted van der Waals heterostructures made from monolayer MoS2, hBN, and graphene. We compare data taken by low-temperature scanning tunneling spectroscopy to results from room-temperature conductive atomic force spectroscopy on monolayer MoS2 with sulfur vacancies and with varying hBN layers. We show that for thick hBN barrier layers, where tunneling currents into the conductive substrate are suppressed, a side-contact still enables addressing the defect states in the scanning tunneling microscopy via the lateral current flow. Few-layer hBN realizes an intermediate regime in which the competition between vertical tunneling and lateral transport needs to be considered. The latter is relevant for device structures with both a thin tunneling barrier and a side-contact to the semiconducting layers.