Graphene band gap heralds new electronics
Scientists in the US and France have produced graphene with a record high band gap of half an electronvolt (0.5 eV), which they claim is sufficient to produce useful graphene transistors. The band gap owes itself to highly periodic bonding on a silicon carbide substrate.
Graphene, a single layer of carbon atoms arranged in a honeycomb-shaped lattice, exhibits a range of superlative properties. Since it was discovered in 2003, it has been found to have exceptional strength, thermal conductivity and electric conductivity. The last property makes the material ideal for the tiny contacts in electronic circuits, but ideally it would also make up the components – particularly transistors – themselves.
To do so, graphene would need to behave not just as a conductor but as a semiconductor, which is the key to the on–off switching operations performed by electronic components. Semiconductors are defined by their band gap: the energy required to excite an electron stuck in the valence band, where it cannot conduct electricity, to the conduction band, where it can. The band gap needs to be large enough so that there is a clear contrast between a transistor’s on and off states, and so that it can process information without generating errors.
Regular graphene has no band gap – its unusually rippled valence and conduction bands actually meet in places, making it more like a metal. Nonetheless, scientists have tried to tease them apart. By fabricating graphene in odd shapes, such as ribbons, band gaps up to 100 meV have been realised, but these are considered too small for electronics.
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http://www.rsc.org/chemistryworld/2015/09/graphene-band-gap-electronics-transistors-semiconductor
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