Observation of Negative Contact Resistances in Graphene Field-Effect Transistors

TL;DR

This study investigates the contact resistance behavior in graphene transistors, revealing that contact resistance can become negative due to doping effects, especially with silver contacts, challenging traditional assumptions.

Contribution

It demonstrates the occurrence of negative contact resistances in graphene transistors and models the doping-induced potential variations causing this phenomenon.

Findings

Negative contact resistance observed with Ag contacts.

Doping effects can outweigh actual contact resistance.

Model explains dip in contact resistance near charge neutrality.

Abstract

The gate-voltage (VG) dependence of the contact resistance (RC) in graphene field-effect transistors is characterized by the transmission line model. The RC-VG characteristics of Ag, Cu, and Au contacts display a dip around the charge neutrality point, and become even negative with Ag contacts. The dip structure is well reproduced by a model calculation that considers a metal-contact-induced potential variation near the metal contact edges. The apparently negative RC originates with the carrier doping from the metal contacts to the graphene channel and appears when the doping effect is more substantial than the actual contact resistance precisely at the contacts. The negative RC can appear at the metal contacts to Dirac-cone systems such as graphene.