Feb 9, 2012
Nanohole lattices: a new route for graphene electronics
Pristine graphene exhibits remarkable transport properties, but its gapless character is a strong limitation for electronic applications. However, in a 2D graphene sheet of nanoholes, a finite bandgap opens up and can be controlled by tuning the size of the holes and their spacing. Such a graphene nanomesh (GNM) offers an excellent opportunity for bandgap engineering and could turn out to be a more effective approach than cutting graphene sheets into nanoribbons. In a recent study published in the journal Nanotechnology, researchers in France have used a simulation approach based on a Green's function technique within an atomistic tight binding model to study the transport characteristics of some GNM devices exhibiting a strong effect of negative differential conductance (NDC).
In the work, the numerical simulations highlighted the advantages of GNM lattices for designing NDC devices with a high peak-to-valley ratio (PVR). The group proposed typical devices based on a pn junction and a uniform n-doped structure. In the former device, the peak current is controlled by the interband tunnelling between the conduction band of the n-side and the valence band of the p-side while the valley current is governed by the bandgap in both sides. It gives rise to a high PVR of NDC, but at the expense of a strong sensitivity to the length of the transition region between p-doped and n-doped zones. In the uniformly n-doped structure, the PVR is smaller because of the enhanced valley current controlled by a small minigap. However, the peak current resulting from normal transmission is higher and not significantly influenced by the transition length.
Remarkably, the team demonstrated that when pristine graphene is introduced in the transition region of the pn junction, the NDC effect is improved significantly. In such a GNM/pristine graphene/GNM heterostructure, due to the gapless character of pristine graphene, the evanescent states do not appear in the transition region, which makes the peak current high and weakly dependent on the transition length while the valley current controlled by the large bandgap in both junction sides is maintained at a low value. This results in a high PVR of a few hundred at room temperature, even for a large transition length.
This work demonstrates the high potential of GNM lattices to introduce all the benefits of bandgap engineering in graphene devices.
The team presented its work in the journal Nanotechnology.
About the author
The study was conducted by researchers from the Institut d'Electronique Fondamentale, Orsay, France, a joint research unit of Université Paris-Sud and Centre National de la Recherche Scientifique (CNRS). Viet Hung Nguyen is a postdoctoral researcher. His current work focuses on electronic and spin polarized transport in graphene-based devices, using a non-equilibrium Green's function quantum transport approach. Fulvio Mazzamuto is PhD student involved in the simulation of thermal and thermoelectronic effects in graphene structures. Jérôme Saint-Martin is assistant professor at Université Paris-Sud, Arnaud Bournel is professor at Université Paris-Sud and Philippe Dollfus is senior researcher at CNRS. They are all currently working on the advanced simulation of electron and phonon transport in nanodevices.