The role of contact resistance in graphene field-effect devices

TL;DR

This paper reviews the experimental and theoretical efforts over the past decade to understand and reduce contact resistance in graphene transistors, a key factor limiting device performance and scalability.

Contribution

It provides a comprehensive summary of the properties, fabrication techniques, and charge transport mechanisms affecting graphene-metal contacts, highlighting recent advances and remaining challenges.

Findings

Low contact resistance is crucial for high-performance graphene transistors.

Metal choice and fabrication process significantly influence contact quality.

Understanding charge transport mechanisms aids in developing better contact strategies.

Abstract

The extremely high carrier mobility and the unique band structure, make graphene very useful for field-effect transistor applications. According to several works, the primary limitation to graphene based transistor performance is not related to the material quality, but to extrinsic factors that affect the electronic transport properties. One of the most important parasitic element is the contact resistance appearing between graphene and the metal electrodes functioning as the source and the drain. Ohmic contacts to graphene, with low contact resistances, are necessary for injection and extraction of majority charge carriers to prevent transistor parameter fluctuations caused by variations of the contact resistance. The International Technology Roadmap for Semiconductors, toward integration and down-scaling of graphene electronic devices, identifies as a challenge the development of a CMOS compatible process that enables reproducible formation of low contact resistance. However, the contact resistance is still not well understood despite it is a crucial barrier towards further improvements. In this paper, we review the experimental and theoretical activity that in the last decade has been focusing on the reduction of the contact resistance in graphene transistors. We will summarize the specific properties of graphene-metal contacts with particular attention to the nature of metals, impact of fabrication process, Fermi level pinning, interface modifications induced through surface processes, charge transport mechanism, and edge contact formation.