Influence of Metal-Graphene Contact on the Operation and Scalability of Graphene Field-Effect-Transistors

TL;DR

This paper uses advanced simulations to analyze how metal contacts affect the operation and scalability of graphene FETs, highlighting the roles of doping, DOS broadening, and tunneling effects.

Contribution

It provides a detailed numerical analysis of metal-graphene contact effects on GFET performance and scalability, emphasizing the dominance of direct tunneling over MIS in channel length scaling.

Findings

Doping effect causes asymmetric transfer characteristics.

Higher M-G coupling increases on-current due to DOS broadening.

Channel length scalability is mainly limited by direct S->D tunneling.

Abstract

We explore the effects of metal contacts on the operation and scalability of 2D Graphene Field-Effect-Transistors (GFETs) using detailed numerical device simulations based on the non-equilibrium Green's function formalism self-consistently solved with the Poisson equation at the ballistic limit. Our treatment of metal-graphene (M-G) contacts captures: (1) the doping effect due to the shift of the Fermi level in graphene contacts, (2) the density-of-states (DOS) broadening effect inside graphene contacts due to Metal-Induced-States (MIS). Our results confirm the asymmetric transfer characteristics in GFETs due to the doping effect by metal contacts. Furthermore, at higher M-G coupling strengths the contact DOS broadening effect increases the on-current, while the impact on the minimum current (Imin) in the off-state depends on the source to drain bias voltage and the work-function difference between graphene and the contact metal. Interestingly, with scaling of the channel length, the MIS inside the channel has a weak influence on Imin even at large M-G coupling strengths, while direct source-to-drain (S -> D) tunneling has a stronger influence. Therefore, channel length scalability of GFETs with sufficient gate control will be mainly limited by direct S -> D tunneling, and not by the MIS.