First-principles NEGF simulations of metal-graphene contacts

For nanoscale electronic devices, the precise atomic structure of the metal contact significantly affects the performance of the device. We use an accurate DFT-based non-equilibrium Green’s function (NEGF) method with variationally-optimized localized orbitals to study contacts between different metals and graphene and/or graphene nanoribbons (GNRs). For surface metal contacts not chemically bound to graphene, we find that Ti contacts have lower resistance than other metals, such as Au, Ca, Ir, Pt, and Sr. We will discuss channel length effects on the off-state current and the required minimum channel and contact lengths for applications. Depending on the type of the armchair GNR, the transmission gap and current vary dramatically. For an edge contact, zero-bias resistivity with different channel lengths shows diverse patterns compared to that of a surface contact. We also study the oxygen contamination at an edge contact, which lowers the ballistic resistance and introduces a new transmission spectrum.