Researchers may be a step closer to making the material graphene a viable building block of semiconductor devices.
This new method allows scientists to change the amount of electrons present in a region of graphene, and could even "rewire" the graphene circuit elements without the need to physically alter the electronic device, the University of Pennsylvania reported.
Silicon is typically used for making circuit elements because its charge-carrier density (the number of free electrons it contains) can be increased of decreased by adding chemical impurities in what is known of as a "doping process," this results in "p-type" and "n-type" semiconductors. The junctions between p- and n-type semiconductors are thought of as the "building blocks" of electronic devices.
Chemically doping graphene can change some of its electrical properties, and the same effect can be achieved by applying local voltage changes to the material (but this can be a hassle).
"We've come up with a non-destructive, reversible way of doping that doesn't involve any physical changes to the graphene," said Andrew Rappe at the University of Pennsylvania, Lane Martin at Berkeley and Moonsub Shim at Illinois.
The new technique involves depositing a layer of graphene on the material lithium niobate, which is ferroelectric (a polar material with either a positive or negative charge). The researchers found applying an electric field pulse could change the surface charges.
"That's an unstable situation in that the positively charged surface will want to accumulate negative charges and vice versa. To resolve that imbalance, you could have other ions come in and bond or have the oxide lose or gain electrons to cancel out those charges, but we've come up with a third way," Rappe said. "Here we have graphene standing by, on the surface of the oxide but not binding to it. Now, if the oxide surface says, 'I wish I had more negative charge,' instead of the oxide gathering ions from the environment or gaining electrons, the graphene says 'I can hold the electrons for you, and they'll be right nearby.'"
This allows the graphene to take on other characters depending on the nature of the domain underneath, leading to a simple way to create a p-n junction on a flake of the revolutionary material.
"What's even more exciting are the enabling of optoelectronics using graphene and the possibility of waveguiding, lensing and periodically manipulating electrons confined in an atomically thin material," Rappe said.
The findings were published in a recent edition of the journal Nature Communications.
