Toward more functional gallium oxide

Although gallium oxide — β-Ga₂O₃ — is a promising electrical component, little is known about the electronic structure of acceptors within the material. With that in mind, a team of researchers form the Air Force Institute of Technology, Northrup Grumman Corporation, Northrop Grumman Synoptics and West Virginia University have modeled the neutral magnesium acceptor, of which they report in Applied Physics Letters.

The team grew a crystal doped with magnesium ions that serve as the neutral magnesium acceptors and were identified in a microwave spectrometer after the team used x-rays to irradiate the crystal at 77 Kelvin. The researchers were then able to interpret the spectrum’s complex hyperfine pattern with an open-access EasySpin simulation software program. That allowed them to create a detailed model of the acceptor, which displayed that the hole is localized on one adjacent oxygen ion—quite unlike the neutral magnesium acceptors within gallium nitride (where the hole is centered on the magnesium ion). “The neutral magnesium acceptor in gallium oxide is an excellent example of an acceptor-bound small polaron, of the type often seen in the more ionic oxide materials,” explains co-author Larry Halliburton of West Virginia University.

Halliburton says the results highlight the differences between oxides and nitrides. Specifically, resolved hyperfine interactions with gallium nuclei show that gallium oxide hosts a deeper acceptor and that the conventional semiconductor description used for gallium nitride is not appropriate for gallium oxide. According to Halliburton, the team would like to follow-up experimentally and observe self-trapped holes, similar to magnesium acceptors and explore other acceptor dopants within gallium oxide to better understand the crystal.

Source: “Electron paramagnetic resonance study of neutral Mg acceptors in β-Ga₂O₃ crystals,” by B. E. Kananen, L. E. Halliburton, E. M. Scherrer, K. T. Stevens, G. K. Foundos, K. B. Chang, and N. C. Giles, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.4990454 .