24-04-2019 | | By Rob Coppinger
Ohio State University researchers have found that tin arsenide can provide all the conductivity needed for electronics, reducing the range of materials used, potentially making devices simpler and more energy efficient.
All electronic devices need to conduct electricity and electrons and holes within their atomic structure bring about conductivity, but different materials are needed to provide the electrons and the holes. In a material’s atomic structure each electron has a negative charge. A hole is the absence of an electron in a particular place in an atom where an electron could sit, and that hole is deemed to have a positive charge. Although a hole is not a physical particle, like an electron, it can move from one atom to another within a semiconductor. Tin arsenide, also known by its formula, NaSn2As2, has been found to be able to provide both, electrons and holes.
“It is this dogma in science, that you have electrons, or you have holes, but you don’t have both. But our findings flip that upside down,” says Ohio State University professor of materials science and engineering, Wolfgang Windl. “And it’s not that an electron becomes a hole, because it’s the same assembly of particles. Here, if you look at the material one way, it looks like an electron, but if you look another way, it looks like a hole.”
Detailed view of an integrated circuit through the typical four layers of planarized copper interconnect, the polysilicon (pink), wells (greyish), and substrate (green). By David Carron at English Wikipedia, CC BY-SA 3.0, Link
Tin arsenide’s dual ability was discovered by the then Ohio graduate student researcher, Bin He. While measuring the properties of a tin arsenide crystal, He noticed that the material behaved like an electron-holder and also like a hole-holder at times. He thought he had made a mistake and spent time repeating his experiment, but he continued to get the same result. Tin arsenide is believed to be able to be an electron-holder and a hole-holder because of a unique electronic structure. The Ohio State researchers have called this characteristic goniopolarity.
NaSn2As2 is called a two-dimensional semimetal and also a layered crystal. Because it can provide a single material for conductivity in any electronic device made of it, it is expected to be more energy efficient because the electrons have fewer materials to pass through. This simpler structure is also believed by the Ohio researchers to be more reliable with fewer failures. Candidate devices for the material include smartphone camera light sensors, television light emitting diodes, solar cells and laptops’ transistors.
Tin arsenide is also expected to be only one of many materials that potentially exhibit such a capability. He’s now former team are looking for other such layered materials. This Ohio State research was funded by the United States’ (US) National Science Foundation, the US Air Force Office of Scientific Research and the Camille and Henry Dreyfus Foundation. He has since accepted a post-doctorate position at the Max Planck Institute in Dresden, Germany.