Black phosphorus could spur the next wave of tiny transistors

Crystal structure of black phosphorus - could this be the new silicon?(Credit: Vahid Tayari/McGill University)

Black Phosphorus Valley, anyone? Scientists searching for a way to cram more transistors onto a chip have been examining the potential of graphene for several years, but graphene isn't the only two-dimensional material on the block. Researchers at McGill University and Université de Montréal have provided insight into another promising candidate that could help chip designers keep pace with Moore's Law – black phosphorus.

Graphene is a one-atom thick material with high electrical conductivity, but as a zero bandgap semiconductor, it acts like a metal. This means that transistors made of the material cannot be easily turned on and off.

Black phosphorus also can be separated into one-atom thick layers known as phosphorene. Unlike graphene, phosphorene acts as a semiconductor that can easily be switched on and off. This property could substantially lower the energy needed to power transistors, in turn lowering the heat that they generate.

"Transistors work more efficiently when they are thin, with electrons moving in only two dimensions," says associate professor and senior author of the new study, Thomas Szkopek. "Nothing gets thinner than a single layer of atoms."

There is a problem though. As it approaches this two-dimensional state black phosphorous is damaged by light, which spells trouble for the creation of single layer transistors.

In experiments at the highest-powered magnet laboratory in the world, the National High Magnetic Field Laboratory in Florida, the research team discovered that even in thicker sheets of black phosphorous, the electrons still move only in two dimensions.

"What’s surprising in these results is that the electrons are able to be pulled into a sheet of charge which is two-dimensional, even though they occupy a volume that is several atomic layers in thickness," says Szkopek.

The finding that the 2D electronic structure is independent of the 2D atomic structure could have implications for manufacturing the material on a large scale, though that may still be someway off.

"There is a great emerging interest around the world in black phosphorus,” Szkopek says. “We are still a long way from seeing atomic layer transistors in a commercial product, but we have now moved one step closer.”

The findings were published this month in Nature Communications.

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