Graphene nanoribbon devices at high bias.

Melinda Y Han,Philip Kim

doi:10.1186/s40580-014-0001-y

Abstract

We present the electron transport in graphene nanoribbons (GNRs) at high electric bias conduction. When graphene is patterned into a few tens of nanometer width of a ribbon shape, the carriers are confined to a quasi-one-dimensional (1D) system. Combining with the disorders in the system, this quantum confinement can lead into a transport gap in the energy spectrum of the GNRs. Similar to CNTs, this gap depends on the width of the GNR. In this review, we examine the electronic properties of lithographically fabricated GNRs, focusing on the high bias transport characteristics of GNRs as a function of density tuned by a gate voltage. We investigate the transport behavior of devices biased up to a few volts, a regime more relevant for electronics applications. We find that the high bias transport behavior in this limit can be described by hot electron scattered by the surface phonon emission, leading to a carrier velocity saturation. We also showed an enhanced current saturation effect in the GNRs with an efficient gate coupling. This effect results from the introduction of the charge neutrality point into the channel, and is similar to pinch-off in MOSFET devices. We also observe that heating effects in graphene at high bias are significant.

Highlights

The discovery of graphene [1] has enabled intense fundamental and applied research activities in this novel two-dimensional (2D) carbon based electronic system
We found that At the charge neutrality point, a length-independent transport gap forms whose size is inversely proportional to the graphene nanoribbons (GNRs) width
In this review, we examine the electronic properties of lithographically fabricated GNRs with widths in the tens of nanometers

Summary

Background

The discovery of graphene [1] has enabled intense fundamental and applied research activities in this novel two-dimensional (2D) carbon based electronic system. Graphene devices operated at high source-drain bias show a saturating I − V characteristic This decrease in conductivity at high applied electric field is described by carrier velocity saturation due to optical phonon emission. In a well known experiment, Yao et al [26] found that current in metallic single wall carbon nanotubes saturates at high electric field Their result is explained in terms of zone-boundary optical phonon emission from high energy electrons. A slightly different behavior was reported in semiconducting single wall carbon nanotubes by Chen and Fuhrer [27] In these devices, current does not saturate completely, and the transport is described by an electric field dependent carrier velocity.

Saturating behavior fits a velocity saturation model

Top-gated graphene devices show an enhanced current saturation effect

Heating effects can overcome transport gap at high bias

Conclusions