Towards pristine graphene-metal interface and microstructures: Laser assisted direct patterning on Epitaxial graphene

TL;DR

This paper introduces a femtosecond laser patterning technique for epitaxial graphene, enabling detailed study of intrinsic and extrinsic factors affecting graphene-metal contact resistance, and highlights the importance of intentional edge contact formation.

Contribution

It demonstrates a laser-assisted patterning method to analyze contact resistance factors in epitaxial graphene and shows that intentional edge contact formation is necessary for optimal conductivity.

Findings

Clean graphene-metal interfaces are not enough for quantum-limited contact resistance.

Edge state conduction does not spontaneously form in epitaxial graphene on SiC.

Intentional end-contact formation is essential for low contact resistance.

Abstract

Graphene-metal contact resistance is governed by both intrinsic and extrinsic factors. Intrinsically, both the density of states bottleneck near the Dirac point and carrier reflection at the graphene-metal interface lead to a high contact resistance. Moreover, graphene exhibits insulating behavior for out-of-the-plane conduction. Extrinsically, surface contamination introduced by photoresist residue or different adsorbed species during standard lithography processing alters graphene's intrinsic properties by uncontrolled doping and increased scattering which results in high and inconsistent contact resistance. Here we demonstrate a femto-second laser assisted direct patterning of graphene microstructures that enables us to study both intrinsic and extrinsic effects on the graphene-metal interface. We show that a clean graphene-metal interface is not sufficient to obtain contact resistance approaching the intrinsic limit set by the quantum resistance. We also demonstrated that unlike CVD graphene, edge state conduction (or end-contact) is not spontaneously formed by metal deposition in case of graphene grown on SiC(0001). We conclude that for epitaxial graphene, intentional end-contact formation is necessary to obtain contact resistance near the quantum contact resistance limit.