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New material tops silicon, graphene in electron mobility

Posted: 17 Mar 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Wigner crystal? graphene? crystalline lattices? state of matter?

Nobel laureate Eugene Wigner's dream 80 years ago has come closer to reality as scientists discovered how to put crystalline lattices of pure electrons in the bottom of a silicon-encased quantum well. The resulting material is believed to possess electron mobility that is more than 1,700 times that of crystalline silicon and 200 times greater than that of graphene.

So far, the work is still at the level of fundamental physics, but if researchers make the kind of advances they anticipate they could open a door to significant applications in semiconductors.

"We are not ready for appsonly the basic science. We are looking for the quantum Wigner crystal predicted theoretically in 1934 and sought for ever after. With these new samples, we should be able to answer the question 'yes or no,'" professor Sergey Kravchenko at Northeastern University told EE Times.

"We have the techniques that will allow us to detect this new state of matter. If it exists as Wigner predicted, then one of the most important questions in [what's known as] condensed-matter physics will have been answered," he said.

Kravchenko is hopeful that if his team's results are confirmed, the ultra-high-electron mobility will attract semiconductor researchers to figure out how to make use of it. As a physicist, his goal is to prove this state of matter is possible, and leave it up to the semiconductor researchers to create real applications with it.

Eight layered stack

Eight layered stack used by the researchers to create a quantum well filled with a crystalline lattice of pure electrons. (Source: Northeastern University)

"We are just trying to observe this unique state of matter predicted a long time ago, but never seen in spite of many attempts," Kravchenko told us.

Describing his work, the researcher noted that there are no atoms in the confinement of the quantum well, only electrons. Thus, the research is effectively creating what is called an electron "gas" since particles are normally bouncing around like molecules in a room. However, under the right conditions that electron gas crystalises into a lattice with an electron mobility of 2.4 million cm2/Vs, compared to 10,0000cm2/Vs for graphene and 1,400cm2/Vs for silicon.

"Being a 2D electron gas means the electrons can only move in a plane like billiard balls. They cannot jump over each other or move in a perpendicular direction," Kravchenko said. "We created this system in semiconductors that squish the electrons between potential barriers."

Wigner Crystal

Structure of a two-dimensional Wigner crystal with 600 electronstriangles and squares mark positions of the topological defects. By Arunas.rv (Source: Wikipedia: Wigner Crystal)

Wigner predicted that such a state of matter was possible back in 1934, 29 years before he received the Nobel Prize in 1963 for the discovery of symmetry principles in elementary particles. But it was not until Kravchenko's team discovered how to do it that the dream was realised. Other contributors to the work came from National Taiwan University and the Institute of Solid-State Physics (Moscow).

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