Credit: © 2008 IEEE

Graphene, comprising a flat sheet of carbon, boasts remarkable conductivity, and so is a tempting material for use in transistor channels. One roadblock is the fact that graphene has zero bandgap — the space between energy levels that gives semiconductors the capability of switching between conducting and insulating phases. As a result, graphene transistors are hard to turn off, with on/off ratios typically below ten. Now, Tim Echtermeyer at the Advanced Microelectronic Center in Aachen and colleagues1 have managed to make a graphene transistor with an on/off ratio of over 106.

Some researchers have attempted to introduce a band gap in graphene by cutting it into very narrow ribbons, but such structures have proven very difficult to make. Echtermeyer and co-workers instead built a transistor with normal graphene. When they switch the transistor with the usual gate voltage, they found that a large enough voltage causes a significant and reversible change in current.

The researchers attribute this change to a chemical modification of the graphene surface itself. They speculate that water close to the graphene surface can be split into hydrogen and hydroxide ions by the high electric field. These ions attach to the graphene crystal producing either graphane, which has a large bandgap, or graphene oxide, an insulator.