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

摘要

We explore the effects of metal contacts on the operation and scalability of2D Graphene Field-Effect-Transistors (GFETs) using detailed numerical devicesimulations based on the non-equilibrium Green's function formalismself-consistently solved with the Poisson equation at the ballistic limit. Ourtreatment of metal-graphene (M-G) contacts captures: (1) the doping effect dueto 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 dueto the doping effect by metal contacts. Furthermore, at higher M-G couplingstrengths the contact DOS broadening effect increases the on-current, while theimpact on the minimum current (Imin) in the off-state depends on the source todrain bias voltage and the work-function difference between graphene and thecontact metal. Interestingly, with scaling of the channel length, the MISinside the channel has a weak influence on Imin even at large M-G couplingstrengths, while direct source-to-drain (S -> D) tunneling has a strongerinfluence. Therefore, channel length scalability of GFETs with sufficient gatecontrol will be mainly limited by direct S -> D tunneling, and not by the MIS.