BERKELEY, CA Graphene is the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. But there's a catch: graphene has no bandgap.
"Having no bandgap greatly limits graphene's uses in electronics," says Feng Wang of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, where he is a member of the Materials Sciences Division. "For one thing, you can build field-effect transistors with graphene, but if there's no bandgap you can't turn them off! If you could achieve a graphene bandgap, however, you should be able to make very good transistors."
Wang, who is also an assistant professor in the Department of Physics at the University of California at Berkeley, has achieved just that. He and his colleagues have engineered a bandgap in bilayer graphene that can be precisely controlled from 0 to 250 milli-electron volts (250 meV, or .25 eV).
Moreover, their experiment was conducted at room temperature, requiring no refrigeration of the device. Among the applications made possible by this breakthrough are new kinds of nanotransistors and because of its narrow bandgap nano-LEDs and other nanoscale optical devices in the infrared range.
The researchers describe their work in the June 11 issue of Nature.
Constructing a bilayer graphene transistor
As with monolayer graphene, whose carbon atoms are arranged in "chickenwire" configuration, bilayer graphene which consists of two graphene layers lying one on the other also has a zero bandgap and thus behaves like a metal. But a bandgap can be introduced if the mirror-like symmetry of the two layers is disturbed; the material then behaves like a semiconductor.
Previously, in 2006, researchers at Berkeley Lab's Advanced Light Source (ALS) observed a bandgap in bilayer graphene in which one of the layers was chemi
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DOE/Lawrence Berkeley National Laboratory