Tunneling Spectroscopy of Two-Dimensional Materials Based on Via Contacts

TL;DR

This paper presents a new via contact-based tunneling architecture for 2D materials, enabling detailed spectroscopic analysis and overcoming previous limitations in planar tunneling device fabrication.

Contribution

The study introduces a novel via contact method for tunneling spectroscopy in 2D materials, improving device quality and measurement precision.

Findings

Characterized barrier strength and interface disorder in NbSe2 devices.

Demonstrated a crossover from diffusive to point contacts in small-area devices.

Showed suppression of phonon and defect effects in graphene with thinner barriers.

Abstract

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 ($h$BN). We use the via-based tunneling method to study the single-particle density of states of two different two-dimensional (2D) materials, NbSe$_2$ and graphene. In NbSe$_2$ devices, we characterize the barrier strength and interface disorder for barrier thicknesses of 0, 1 and 2 layers of $h$BN and study the dependence on tunnel-contact area down to $(44 \pm 14)^2 $ nm$^2$. For 0-layer $h$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 $h$BN barrier. This via-based architecture overcomes limitations of other planar tunneling designs and produces high-quality, ultra-clean tunneling structures from a variety of 2D materials.