Dependable contact related parameter extraction in graphene-metal junctions

Abstract

The accurate extraction and the reliable, repeatable reduction of graphene - metal contact resistance (R${}_C$) are still open issues in graphene technology. Here, we demonstrate the importance of following clear protocols when extracting R${}_C$ using the transfer length method (TLM). We use the example of back-gated graphene TLM structures with nickel contacts, a complementary metal oxide semiconductor compatible metal. The accurate extraction of R${}_C$ is significantly affected by generally observable Dirac voltage shifts with increasing channel lengths in ambient conditions. R${}_C$ is generally a function of the carrier density in graphene. Hence, the position of the Fermi level and the gate voltage impact the extraction of R${}_C$. Measurements in high vacuum, on the other hand, result in dependable extraction of R${}_C$ as a function of gate voltage owing to minimal spread in Dirac voltages. We further assess the accurate measurement and extraction of important parameters like contact-end resistance, transfer length, sheet resistance of graphene under the metal contact and specific contact resistivity as a function of the back-gate voltage. The presented methodology has also been applied to devices with gold and copper contacts, with similar conclusions.

arXiv comment23 pages

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