Graphene semiconductor steps toward ultra-fast computers

An international research team has made a functional semiconductor out of graphene, saying it paves the way for faster, smaller electronics than silicon-based technology can achieve.

Semiconductors – materials that both do and don’t conduct electricity, depending on what you do to them – are used as tiny ‘switches’ in electronics.

Almost all the world’s electronics use silicon semiconductors. Manufacturers are reaching a limit on the efficiency of silicon – it’s becoming difficult to make faster or more powerful computers with this material.

This has spurred physicists to look for new semiconductors.

“We now have an extremely robust graphene semiconductor with 10 times the mobility of silicon, and which also has unique properties not available in silicon,” says Professor Walter de Heer, a physicist at the Georgia Institute of Technology, US, and senior author on the research published in Nature on Thursday.

Person holds glass circle in front of eye
Walter de Heer, professor of physics at the Georgia Institute of Technology, holds a silicon carbide wafer. Credit: Georgia Institute of Technology

Graphene – made from sheets of carbon atoms connected in a honeycomb-like lattice – is a strong and versatile substance, making it a drawcard for de Heer and his colleagues.

“It’s an extremely robust material, one that can handle very large currents, and can do so without heating up and falling apart,” de Heer says.

Hands holding molecular model
Molecular models of graphene and silicon carbide. Credit: Georgia Institute of Technology

It’s taken more than a decade to craft the graphene semiconductor. The challenge lies in a property materials have called a ‘band gap’ – a difference in energy that allows an electron to move around molecules, letting electricity flow. Semiconductors have a small band gap, while more insulating materials have a larger one.

Graphene, like other materials that conduct electricity well, doesn’t have a band gap.

“A long-standing problem in graphene electronics is that graphene didn’t have the right band gap and couldn’t switch on and off at the correct ratio,” says co-author Professor Lei Ma, director of the Tianjin International Center for Nanoparticles and Nanosystems at Tianjin University in China.

“Over the years, many have tried to address this with a variety of methods. Our technology achieves the band gap, and is a crucial step in realising graphene-based electronics.”

De Heer’s patented induction furnace used to produce graphene on silicon carbide. Credit: Georgia Institute of Technology

With the help of some elaborate furnaces, the researchers made “epitaxial” graphene: a layer of the substance grown on a crystal (made, in this case, from silicon carbide).

This yielded a material that worked as a semiconductor, with 10 times greater mobility than silicon.

Hands holding glass circle cut into squares
A single crystal silicon carbide wafer that has been cut into square chips. Credit: Georgia Institute of Technology

“It’s like driving on a gravel road versus driving on a freeway,” says de Heer. “It’s more efficient, it doesn’t heat up as much, and it allows for higher speeds so that the electrons can move faster.”

So when is that ultra-fast computer coming? Not anytime soon.

Hand holding vial of dark substance
A vial of graphene grown in a furnace at de Heer’s lab at Georgia Tech. Credit: Georgia Institute of Technology

There are still several research problems to solve before the graphene semiconductor can be scaled up to computer chips and computers. That’s before it encounters the tremendously complicated and expensive chip manufacturing industry.

Nevertheless, the researchers write in their paper that the technology has “marked potential to become commercially viable in the future”.

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