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Scientists See Useful Defects In Potential New Semiconductor

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crystal structure of beta-Ga2O3

Crystal structure of beta?Ga2O3 along the [010]m direction with five possible interstitial sites.

A research team has reported seeing atomic scale defects that dictate the properties of beta gallium oxide, a new and powerful semiconductor.

"Unusual Formation of Point-Defect Complexes in the Ultrawide-Band-GapSemiconductorβ-Ga2O3," published in the journal Physical Review X, shows a fundamental aspect of how the semiconductor controls electricity.

"Our job is to try to identify why this material, called beta gallium oxide, acts the way it acts at the fundamental level," says Jared Johnson, lead author of the study and a graduate research associate at The Ohio State University Center for Electron Microscopy and Analysis (CEMAS). "It is important to know why this material has the properties it has, and how it acts as a semiconductor, and we wanted to look at it at the atomic level — to see what we could learn."

Scientists have known about beta gallium oxide for about 50 years, but only in the last several years has it become an intriguing option for engineers looking to build more reliable, more efficient high-powered technologies. The material is especially well-suited for devices used in extreme conditions, such as in the defense industry. The team has been studying beta gallium oxide for its potential to provide high-density power.

For this study, the CEMAS team, overseen by Jinwoo Hwang, assistant professor of materials science and engineering, examined beta gallium oxide under a powerful electron microscope, to see the way the material's atoms interacted. What they saw confirmed a theory first hypothesized about a decade ago by theorists: Beta gallium oxide has a form of imperfection in its structure, something the team refers to as "point defects," which are unlike any defects previously seen in other materials.

Those defects matter: For example, there could be places where electricity could be lost in transit among electrons. With proper manipulation, the defects can also provide opportunities for unprecedented control of the material's properties. But understanding the defects must preceed an understanding of how to control them.

"It is very meaningful that we could actually directly observe these point defects, these abnormalities within the crystal lattice," Johnson says. "And these point defects, these oddballs within the lattice structure, lower the energy stability of the structure."

A lower energy stability means that the material might have some flaws that need addressing in order to conduct electricity efficiently, Johnson says, but they don't mean beta gallium oxide would not necessarily be a good semiconductor. The defects can in fact behave favorably to conduct electricity — if scientists can control them.

Additional authors of the Physical Review X study are Zhen Chen and David A. Muller of Cornell University, Joel B. Varley of Lawrence Livermore National Laboratory, Christine M. Jackson, Esmat Farzana, Zeng Zhang, Aaron R. Arehart, Hsien-Lien Huang, and Steven A. Ringel of Ohio State University, Arda Genc of Thermo Fisher Scientific, and Chris G. Van de Walle of the University of California, Santa Barbara.

"This material has very good properties for those high-powered technologies," Johnson says. "But it is important that we're seeing this on the fundamental level — we're almost understanding the science behind this material and how it works, because this defect, these abnormalities, could affect the way it functions as a semiconductor."

This work was funded by the U.S. Department of Defense Air Force Office of Scientific Research.


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