Researchers create first functional graphene-based semiconductor

Researchers at the Georgia Institute of Technology have created the world’s first functional semiconductor made from graphene, a single sheet of carbon atoms held together by the strongest bonds known. Semiconductors, which are materials that conduct electricity under specific conditions, are fundamental components of electronic devices. The team’s breakthrough opens the door to a new way of doing electronics.

Their discovery comes at a time when silicon, the material from which almost all modern electronic devices are made, is reaching its limits in the face of ever-faster computing and ever-smaller electronic devices.

Walter de Heer, professor of physics at Georgia Tech, led a team of researchers based in Atlanta, Georgia, and Tianjin, China, to produce a graphene semiconductor compatible with conventional microelectronics processing methods, a necessity for any viable alternative to silicon.

In this latest research, published in Nature, de Heer and his team overcame the major obstacle that had plagued graphene research for decades and was the reason many thought graphene electronics would never work. Known as the “band gap,” this is a crucial electronic property that allows semiconductors to turn on and off. Graphene did not have a bandgap until now.

“We now have an extremely robust graphene semiconductor that has 10 times the mobility of silicon and also has unique properties not available in silicon,” de Heer said. “But the story of our work over the last 10 years has been, ‘Can we make this material good enough to work?'”

A new type of semiconductor

De Heer began exploring carbon-based materials as potential semiconductors early in his career, then turned to exploring two-dimensional graphene in 2001. He knew then that graphene had potential to electronics.

“We were motivated by the hope of introducing three special properties of graphene into electronics,” he said. “It is an extremely robust material, capable of withstanding very high currents, without heating up or collapsing.”

De Heer achieved a breakthrough when he and his team discovered how to grow graphene on silicon carbide wafers using special ovens. They produced epitaxial graphene, which is a single layer that grows on a crystal face of silicon carbide. The team found that when made correctly, epitaxial graphene chemically bonded to silicon carbide and began to show semiconducting properties.

Over the next decade, they persisted in perfecting the material at Georgia Tech, then in collaboration with colleagues at the Tianjin International Center for Nanoparticles and Nanosystems at Tianjin University in China. De Heer founded the center in 2014 with Lei Ma, director of the center and co-author of the article.

How they did it

In its natural form, graphene is neither a semiconductor nor a metal, but a semi-metal. A bandgap is a material that can be turned on and off when an electric field is applied to it, which is how all transistors and silicon electronics work. The major question in researching graphene electronics was how to turn it on and off so that it functions like silicon.

But to make a working transistor, a semiconductor material must be heavily manipulated, which can damage its properties. To prove that their platform could function as a viable semiconductor, the team needed to measure its electronic properties without damaging it.

They placed atoms on the graphene that “donated” electrons to the system – a technique called doping, used to see if the material was a good conductor. It worked without damaging the material or its properties.

The team’s measurements showed that their graphene semiconductor has 10 times the mobility of silicon. In other words, electrons move with very little resistance, which in electronics translates to faster calculation. “It’s like driving on a gravel road rather than a highway,” de Heer said. “It’s more efficient, it heats up less and it allows for higher speeds so the electrons can move faster.”

The team’s product is currently the only two-dimensional semiconductor with all the properties necessary for use in nanoelectronics, and its electrical properties are far superior to those of all other 2D semiconductors currently in development.

“A long-standing problem in graphene electronics is that graphene did not have the right bandgap and could not turn on and off at the right ratio,” said Ma. “Over the years, many have tried to solve this problem with various methods. Our technology reaches the bandgap and is a crucial step in realizing graphene-based electronics.”

Move forward

Epitaxial graphene could cause a paradigm shift in the field of electronics and enable the development of completely new technologies taking advantage of its unique properties. The material makes it possible to use the wave properties of electron quantum mechanics, which is a requirement of quantum computing.

“Our motivation to create graphene electronics has been around for a long time, and the rest was just bringing our project to fruition,” de Heer said. “We had to learn how to process the material, improve it more and more and finally measure its properties. It took a very, very long time.”

According to de Heer, it is not uncommon to see the arrival of a new generation of electronic devices. Before silicon there were vacuum tubes, and before that there were wires and telegraphs. Silicon is one of many milestones in the history of electronics, and the next milestone could be graphene.

“For me, it’s like a Wright Brothers moment,” de Heer said. “They built a plane that could fly 300 feet in the air. But skeptics wondered why the world would need to fly when it already had trains and fast ships. But they persisted, and it was beginning of technology capable of transporting people across the air and oceans.”