Effect of ribbon width on electrical transport properties of graphene nanoribbons

Abstract

There has been growing interest in developing nanoelectronic devices based on graphene because of its superior electrical properties. In particular, patterning graphene into a nanoribbon can open a bandgap that can be tuned by changing the ribbon width, imparting semiconducting properties. In this study, we report the effect of ribbon width on electrical transport properties of graphene nanoribbons (GNRs). Monolayer graphene sheets and Si nanowires (NWs) were prepared by chemical vapor deposition and a combination of nanosphere lithography and metal-assisted electroless etching from a Si wafer, respectively. Back-gated GNR field-effect transistors were fabricated on a heavily p-doped Si substrate coated with a 300 nm-thick SiO₂ layer, by O₂ reactive ion etching of graphene sheets using etch masks based on Si NWs aligned on the graphene between the two electrodes by a dielectrophoresis method. This resulted in GNRs with various widths in a highly controllable manner, where the on/off current ratio was inversely proportional to ribbon width. The field-effect mobility decreased with decreasing GNR widths due to carrier scattering at the GNR edges. These results demonstrate the formation of a bandgap in GNRs due to enhanced carrier confinement in the transverse direction and edge effects when the GNR width is reduced.

Keywords: Electrical transport; Graphene; Graphene nanoribbon; Si nanowire.

Fig. 1

a Raman spectrum and b optical image of a monolayer graphene sheet transferred on a Si/SiO₂ substrate

Fig. 2

a Schematic illustration of the preparation of a Si NW array using a Ag film with uniform-sized holes as an etch mask, where PS beads were used for patterning the Ag film. b–m FESEM images of the process steps for fabricating vertically aligned, ordered Si NW arrays

Fig. 3

Variations of diameter of Si NWs formed with PS beads with diameters of a 460, b 300, and c 100 nm as a function of etching time

Fig. 4

a Schematic illustration of the fabrication of a GNR FET using a Si NW as a hard etch mask. FESEM images of b a Si NW aligned on graphene between two electrodes, where unscreened graphene was removed, and c a GNR after the removal of the Si NW. d AFM images of GNRs with two different ribbon widths (left: 500 nm and right: 100 nm)

Fig. 5

a I_DS–V_G characteristics of GNR FETs with various GNR widths. b On-state current and on/off current ratio, and c bandgap energy of GNR FETs as a function of GNR width. d Electron and hole field-effect mobilities of GNR FETs as a function of GNR width

Fig. 6

I_DS–V_G characteristics of FETs based on a unpatterned graphene and b 100-nm wide GNR, measured at temperatures of 100–300 K