Scientists explore ‘wonder material’ to replace silicon in semiconductors

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Researchers have discovered a way to manipulate electrons in graphene, a 2-D material that could soon replace silicon in the electronics industry.

The team of researchers included Lane Martin, associate professor at UC Berkeley; Andrew Rappe, professor at the University of Pennsylvania; and Moonsub Shim, associate professor at the University of Illinois. Their study explores the ways in which graphene could replace silicon, an important component of most semiconductors, because of the speed in which electrons can move through graphene’s material.

Martin described graphene as a “wonder material” yet to be used in computers and devices. Very thin and nearly transparent, graphene resembles a sheet one atom thick. Because of its structure, graphene is particularly strong for its low weight, conducting heat and electricity efficiently.

“Graphene represents one class of materials that could rival silicon in terms of costs, functionality and scalability in the coming years,” Martin said.

Unlike silicon, graphene lacks the properties for insulation and conduction. Silicon is useful for its “charge-carrier density” — that is, the number of free electrons it holds — which can be increased or decreased through inserting chemical impurities. This process creates “P-type” and “N-type” semiconductors, allowing silicon to have positive or negative charge carriers.

According to researchers, combining P-type and N-type semiconductors into a “junction” forms the basis of many electronic devices. But switching the negative and positive charges in graphene this way, however, sacrifices some of the material’s unique electrical properties.

Researchers, however, discovered a way to preserve graphene’s electrical properties by pairing it with a ferroelectric, or polar, substance called lithium niobate, which contains properties that assist in creating P-N junctions.

By manufacturing lithium niobate to have “stripes” that alternate polar regions of positive and negative, researchers can create an array of P-N junctions on graphene, similar to the way P-N junctions are used for current semiconductors.

“The key was to move the ‘switching’ part away from the graphene,” Martin said. “We can apply electric fields to the ferroelectric, locally switching the direction of the polarization which, in turn, drives local switching of the carrier type and concentration in the graphene.”

By altering the number of electrons residing in a given region of the 2-D material, researchers changed the sign of the surface charges without physically changing the graphene, appearing to be a more traditional semiconductor that could be used in many devices today.

For Rappe, graphene holds promise as a material because of its electronic and mechanical properties, which could someday enable and configure flexible electronics and low-power computing.

“There are many things that have and will come out of graphene research,” Shim said, “from fundamental physics and chemistry to devices no one may have even thought about yet.”

Robert Tooke covers research and ideas. Contact him at [email protected] and follow him on Twitter @robertono_t.

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