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RESEARCHERS from Michigan Technological University hope to combine graphene and boron nitride nanotube insulators to create heterojunctions for transistors, without using any semiconductor.
Graphene is a zero band-gap conductor, with high electron mobility. Boron nitride nanotubes are wide band-gap insulators.
Together, the two materials form a band gap mis-match that creates a potential barrier that stops electrons, effectively creating a switch.
The researchers aim to create transistors that do not rely on semiconductors, in order to circumvent the fundamental issues of silicon-based transistors, benefit from the high electron mobility of graphene, and create smaller and more heat-efficient transistors.
In contrast to earlier research around graphene, which sought to modify or dope it to make it a semiconductor, the researchers at Michigan Tech aim to leave it as a conductor. Instead, the researchers etched pin-holes in a sheet of exfoliated graphene, and grew boron nitride nanotubes out of the holes using chemical vapour deposition, creating ultra-dense fields of 60nm diameter heterojunctions at the joins of the materials.
The scientists then characterised the material at room temperature using a four-probe scanning electron microscope. They found a switching ratio as high as 105 with a turn-on voltage of 0.5V, a novel property that analysis indicates may be caused by a mismatch of the density of states. Overall, the experiment failed to turn the junction into a transistor, possibly because the highly-conductive lower layers of the multi-layer graphene shielded the junction.
The next goal is to continue experimentation, using a top-gated structure and atomic monolayers of graphene, to ultimately create three-terminal devices that behave like conventional silicon-based transistors, albeit at much higher speeds, and no voltage leaks during the off-state.