Tunneling Spectroscopy of Two-Dimensional Materials Based on Via Contacts.

We introduce a novel planar tunneling architecture for van der Waals heterostructures based on via contacts, namely, metallic contacts embedded into through-holes in hexagonal boron nitride (BN). We use the via-based tunneling method to study the single-particle density of states of two different two-dimensional (2D) materials, NbSe and graphene. In NbSe devices, we characterize the barrier strength and interface disorder for barrier thicknesses of 0, 1, and 2 layers of BN and study the dependence on the tunnel-contact area down to (44 ± 14) nm. For 0-layer BN devices, we demonstrate a crossover from diffusive to point contacts in the small-contact-area limit. In graphene, we show that reducing the tunnel barrier thickness and area can suppress effects due to phonon-assisted tunneling and defects in the BN barrier. This via-based architecture overcomes limitations of other planar tunneling designs and produces high-quality, ultraclean tunneling structures from a variety of 2D materials.