Transport in Graphene Tunnel Junctions

TL;DR

This paper introduces a fabrication method for graphene-based tunnel junctions with metals and provides a theoretical model, analyzing conductance behavior and doping effects through experimental and simulation data.

Contribution

It presents a new technique for creating graphene-metal tunnel junctions and offers a simple theory to interpret tunneling conductance and doping effects.

Findings

Conductance fluctuations relate to graphene's density of states.

Electrostatic gating reveals the Dirac point via conductance inflections.

Different metals induce distinct doping levels in graphene.

Abstract

We present a technique to fabricate tunnel junctions between graphene and Al and Cu, with a Si back gate, as well as a simple theory of tunneling between a metal and graphene. We map the differential conductance of our junctions versus probe and back gate voltage, and observe fluctuations in the conductance that are directly related to the graphene density of states. The conventional strong-suppression of the conductance at the graphene Dirac point can not be clearly demonstrated, but a more robust signature of the Dirac point is found: the inflection in the conductance map caused by the electrostatic gating of graphene by the tunnel probe. We present numerical simulations of our conductance maps, confirming the measurement results. In addition, Al causes strong n-doping of graphene, Cu causes a moderate p-doping, and in high resistance junctions, phonon resonances are observed, as in STM studies.