The researchers have found that when electrons move in a phosphorus transistor, they do so only in two dimensions. "Transistors work more efficiently when they are thin, with electrons moving in only two dimensions," says Thomas Szkopek, an associate professor in McGill's Department of Electrical and Computer Engineering.
When separated into single atomic layers, black phosphorus is known as phosphorene. Unlike graphene, black phosphorus can be readily switched on and off.
"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 optimised for a well designed transistor and black phosphorus fills the semiconducting material role."
In order to determine how electrons move in a phosphorus transistor, the researchers observed them under the influence of a magnetic field in experiments performed at the US National High Magnetic Field Laboratory. "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 is said to be significant because it could potentially facilitate manufacturing the material – though Szkopek notes that 'no one knows how to manufacture this material on a large scale'.
"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."
