Towards Ballistic Transport in Graphene

Abstract

Graphene is a fascinating material for exploring fundamental science questions as well as a potential building block for novel electronic applications. In order to realize the full potential of this material the fabrication techniques of graphene devices, still in their infancy, need to be refined to better isolate the graphene layer from the environment. We present results from a study on the influence of extrinsic factors on the quality of graphene devices including material defects, lithography, doping by metallic leads and the substrate. The main finding is that trapped Coulomb scatterers associated with the substrate are the primary factor reducing the quality of graphene devices. A fabrication scheme is proposed to produce high quality graphene devices dependably and reproducibly. In these devices, the transport properties approach theoretical predictions of ballistic transport.

Ballistic-like supercurrent in suspended graphene Josephson weak links

“…Between the electron and the hole branches, we observed an asymmetry with the hole branch showing higher resistance and weak oscillatory (Fabry-Pérot) gate voltage dependence. Such asymmetry behaviour is commonly observed in clean short-channel graphene devices 15,21 . Its presence has been studied theoretically to be due to the charge-transfer at the metal-graphene interface, which induces asymmetric potential profiles near the contacts for electron and hole doping.…”

Electronic properties of graphene: a perspective from scanning tunneling microscopy and magnetotransport

“…The exfoliated graphene layer can be supported on a substrate or suspended from a supporting structure [19] [20][21][22][23]. Although the question of whether free-standing graphene is truly 2D or contains tiny out-of-plane ripples [18] (as was observed in suspended graphene membranes at room temperature [20]) is still under debate, there is no doubt about its having brought countless opportunities to explore new physical phenomena and to implement novel devices.…”

“…In an ideal ballistic graphene junction, this would yield a charge carrier mean free path equivalent of L/2 (L being the channel length) in the Boltzmann transport conductivity [21]. The suspended graphene (SG) devices described here are fabricated from conventional nonsuspended graphene (NSG) devices with Au/Ti or Au/Cr leads deposited on Si/SiO2 (300nm) substrates [21,23]. After fabrication, the NSG devices are coated with PMMA, and an additional electron beam lithography step is carried out to open etching windows over the graphene channels.…”

Fabrication of graphene p-n-p junctions with contactless top gates

“…18 In most of the experiments to date, either an organic or a metal oxide layer has been used as the local gate dielectric, yet its deposition on a single atomic layer remains a delicate process that may lead to additional dopants and/or scattering sites. Moreover, dramatically enhanced mobility has been recently observed in suspended graphene devices, 19,20 but fabrication of suspended graphene p-n junctions using conventional techniques could prove difficult, since direct deposition of local gate dielectrics may considerably stress or even collapse the atomic layer.…”