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Graphene-based transistors may replace Si semiconductors

07 Aug 2015  | R. Colin Johnson

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To realise the graphene/boron-nitride heterojunctions, the team etched pin-holes in a sheet of exfoliated graphene, then grew the boron nitride nanotubes out of the holes, due to the matching lattices, each forming a transistor-like heterojunction. After characterising them at room temperature with a four-probe scanning tunnelling microscope (STM) during real-time monitoring with a scanning electron microscope (SEM), they found a switching ratio as high as 105 with a turn-on voltage of just 0.5V. Yap believed these novel properties are due to the mismatch of the density of states (DOS) after simulations with density function theory (DFT).

Graphene conducting substrate

The grey graphene conducting substrate has insulating boron nitride nanotubes sprouting from it, forming heterojunctions for the semiconductor-less transistors. (Source: Michigan Tech)

Next the researcher want to work with atomic monolayers of graphene, and ultimately to create three-terminal devices that behave just like silicon transistors, but at much higher speeds and without any semiconductors to leak voltage during the off-state, thus greatly lowering the power consumption and temperature of operation of the materials.

"Our next milestone is to create graphene-BNNT heterojunctions with monolayer graphene sheets," Yap added "We are also exploring designs for three terminal devices, for example, using a surround gate design."

Quantum-tunnelling device

Electrons tunnel from one gold quantum dot to the other on boron nitride nanotubes. Michigan Tech scientists made the quantum-tunnelling device, which acts like a transistor at room temperature, without using semiconducting materials. Yoke Khin Yap graphic (Source: Michigan Tech)

According to Yap, graphene by itself is too fast for applications other than as a conductor, whereas boron nitrides band-gap is too wide to act as anything other than an insulator, but together the two complement each other enabling transistor-like heterojuetions that are much faster than silicon, and yet consume much less power when on, and almost no power when off.

Funding was provided by the U.S. Department of Energy (DoE), the U.S. Army Research Laboratory, Weapons and Materials Directorate and was conducted at the Centre for Nanophase Materials Sciences and the Center for Integrated Nanotechnologies.

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