August 29, 2012
Publishing in ACS Nano, ICREA Research Professor and ICN Group Leader Stephan Roche and co-workers describe electrical transport in transistors made of boron-doped graphene nanoribbons.
ICREA Research Professor Stephan Roche, who heads ICN's Theoretical and Computational Nanoscience Group, and colleagues from various French, Italian and Spanish institutes have just published an article in ACS Nano, entitled "Atomistic boron-doped graphene field-effect transistors: a route toward unipolar characteristics", in which they describe the effects of boron doping on the electrical transport in graphene devices. The paper represents an important step towards the advent of graphene-based electronics.
Graphene, often heralded as "the material of the future" due to its impressive mechanical, optical and electrical characteristics, conducts electricity better than any other material at room temperature and therefore, has been proposed as a future substitute for silicon in electronics. However, the use of graphene devices in mainstream electronics remains elusive because of one major limitation: unlike silicon, graphene is not a semiconductor,
meaning that current in it cannot be switched on and off—a critical feature for electronic circuits. In technical terms, this is down to two features: whereas semiconductors have unipolar current-voltage characteristics and a small band gap (energy gap), graphene has ambipolar current-voltage characteristics and lacks a bandgap.
Prof Roche and his co-workers employed state-of-the-art quantum simulations to ascertain the effects of boron or nitrogen doping on the electrical transport through the channel of graphene nanoribbon-based transistors. They found that the boron and nitrogen impurities confer graphene with seemingly semi-conductor-like features: near unipolar behaviour and a small transport gap. Moreover, in their simulations they were able to fine-tune the behaviour of the transistors by adjusting the doping concentration and density.
The authors' results suggest that for graphene ribbons which have low doping levels and are wider than 10 nanometres—a threshold which roughly correlates with the resolution limits of modern nanofabrication—bandgaps of approximately 1 eV (on the same order as bulk silicon) should be possible.
Whilst recognising that the observed bandgaps are still too small for practical use, they affirm that the results are a positive step towards graphene-based nanoelectronics. As a strategy to create such devices, the authors propose selective localised doping of specific areas in a single graphene sheet, which could then be imprinted with semiconducting materials via known nanoimprinting methods (e.g. E-Beam Lithography).