Edge-Sensitive Semiconducting Behaviour in Low-Defect Narrow Graphene Nanoribbons

Low-defect graphene nanoribbons (GNRs) derived from the unzipping of carbon nanotubes have exhibited large energy band gaps (transport gaps), despite having widths in the order of ~100 nm. Here, we report on the unique semiconducting behaviour of very narrow, low-defect GNRs, with widths of less than 20 nm. Narrow GNRs are highly resistive, and additional annealing is required to reduce their resistivity. The GNRs display ambipolar rather than evident semiconducting behaviour (p- and n-types), exhibiting normalized Ion/ Ioff as great as ~106 (close to those in a few nm-order-width GNRs) and which are very sensitive to the atmosphere and the termination of the GNRs' edges by foreign atoms (hydrogen for n-type and oxygen for p-type). It is also revealed that the activation energy (Ea ~35 meV) estimated from the temperature dependence of the minimum conductance is smaller than those in ~100 nm width GNRs. The observed sharp conductance peak on back-gate voltage (Vbg) dependence and its strong correlation with the Ea value suggest the presence of possible resonant tunnelling through shallow impurity levels with the small Ea introduced by the edge terminations by foreign atoms, which provides the observed unique behaviour, including the high Ion/ Ioff. An energy band gap as large as ~215 meV is also confirmed from the Ioff voltage region on Vbg. These narrow GNRs must open the door to large-scale graphene integration circuits based on CMOS-like behaviour.