Black Phosphorus Based Transistors One Step Closer

Black phosphorus may well emerge as a strong contender for the material that will make it possible to squeeze more transistors on a chip. New research from McGill University and Université de Montréal suggests that black phosphorus could help engineers design more energy-efficient transistors, one of the most challenging issues facing future electronics.

In the study, researchers report that when electrons move in a phosphorus transistor, they move in only in dimensions. Senior author Thomas Szkopek, associate professor in McGill’s Department of Electrical and Computer Engineering, explains:

“Transistors work more efficiently when they are thin, with electrons moving in only two dimensions. Nothing gets thinner than a single layer of atoms.”

Since the discovery of graphene in 2004, scientists have raced to investigate a range of other two-dimensional materials.

One of those alternative materials is black phosphorus. A form of phosphorus that is similar to graphite, it can be separated easily into single atomic layers, known as phosphorene.

Phosphorene overcomes many of the challenges of using graphene in electronics. Unlike graphene, which functions like a metal, black phosphorus is a natural semiconductor, and can be switched on and off easily.

“To lower the operating voltage of transistors, and thereby reduce the heat they generate, we have to get closer and closer to designing the transistor at the atomic level,” Szkopek says. “The toolbox of the future for transistor designers will require a variety of atomic-layered materials: an ideal semiconductor, an ideal metal, and an ideal dielectric. All three components must be optimized for a well designed transistor. Black phosphorus fills the semiconducting-material role.”

“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,” Szkopek says. That finding is significant because it could potentially facilitate manufacturing the material — though at this point “no one knows how to manufacture this material on a large scale.”

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

Two-dimensional magnetotransport in a black phosphorus naked quantum well
V. Tayari et al
Nature Communications, July 7, 2015. DOI: 10.1038/ncomms8702

Photo: The black phosphorus crystal structurecomposed of puckered honeycomb layers with an interlayer distance of 0.5 nm. Image credit: V. Tayari et al.