Electronic transport through side-contacted graphene nanoribbons: effects of overlap, aspect ratio and orientation

We numerically calculate the conductance and shot noise Fano factor of graphene nanoribbons (GNRs) side-contacted to metallic leads. A tight-binding model and Landauer's formalism are used in combination with a modified recursion method for Green's functions. The interfaces are modeled as a contact region between an infinite metallic electrode and a segment of the GNR put on top of it. The key question to answer in this study is how the size and orientation of the GNR and the GNR/electrode interface area influence the transport properties. It turns out that in general the transport characteristics depend strongly on overlap, meant as the ratio between the electrode-supported GNR length and the unsupported one. Moreover, a speed of convergence (with the overlap length) depends on both the transport direction and the aspect ratio of the GNR. It is shown that a short overlap interface is often, but not always, advantageous in nanoelectronics. These findings reconcile some seemingly conflicting opinions reported in the literature.