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In a study published today in听Nature Communications, the researchers report that when electrons move in a phosphorus transistor, they do so only in two dimensions. The finding suggests that black phosphorus could help engineers surmount one of the big challenges for future electronics: designing energy-efficient transistors.

鈥淭ransistors work more efficiently when they are thin, with electrons moving in only two dimensions,鈥� says Thomas Szkopek, an associate professor in McGill鈥檚 Department of Electrical and Computer Engineering and senior author of the new study. 鈥淣othing gets thinner than a single layer of atoms.鈥�

Nano-toolbox for transistor designers

In 2004, physicists at the University of Manchester in the U.K. first isolated and explored the remarkable properties of graphene -- a one-atom-thick layer of carbon. Since then scientists have rushed to听 investigate a range of other two-dimensional materials. One of those is black phosphorus, a form of phosphorus that is similar to graphite and can be separated easily into single atomic layers, known as phosphorene.

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Phosphorene has sparked growing interest because it overcomes many of the challenges of using graphene in electronics. Unlike graphene, which acts like a metal, black phosphorus is a natural semiconductor:听 it can be readily switched on and off.

鈥淭o 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,鈥� Szkopek says.

鈥淭he 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. 听Black phosphorus fills the semiconducting-material role.鈥�

The work resulted from a multidisciplinary collaboration among Szkopek鈥檚 nanoelectronics research group, the nanoscience lab of McGill Physics Prof. Guillaume Gervais, and the nanostructures research group of Prof. Richard Martel in Universit茅 de Montr茅al鈥檚 Department of Chemistry.

The highest-powered magnet laboratory

To examine how the electrons move in a phosphorus transistor, the researchers observed them under the influence of a magnetic field in experiments performed at the National High Magnetic Field Laboratory in Tallahassee, FL, the largest and highest-powered magnet laboratory in the world.听 This research 鈥減rovides important insights into the fundamental physics that dictate the behavior of black phosphorus,鈥� says Tim Murphy, DC Field Facility Director at the Florida facility.

鈥淲hat鈥檚 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,鈥� Szkopek says. That finding is significant because it could potentially facilitate manufacturing the material -- though at this point 鈥渘o one knows how to manufacture this material on a large scale.鈥�

This work was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, the Fonds de recherche du Qu茅bec 鈥� Nature et technologies, Le regroupement qu茅b茅cois sur les mat茅riaux de pointe, and the Canada Research Chairs program.听 A portion of the work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation, the State of Florida and the U.S. Department of Energy.

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