Defect control in Gallium Oxide for next-generation POWer electronics

Power electronics is an integral part of all electric systems. It is used to convert electricity from alternating current (AC) to direct current (DC) and to change the voltage level between high and low voltages. Power electronics is thus a key element in the power grid itself, but also central in providing power, e.g., from solar cells and wind-turbines into the grid. It is also central in charging electric vehicles and the transmission of power from the batteries to the motor. We also find them in all our electric appliances in our homes, like in electric stoves, mobile phones and computers to mention a few. In other words, power electronics is a key enabler in realizing an electrification of our societies. The project named «Defect control in Gallium Oxide for next-generation POWer electronics (GO-POW)» will address the need to understand key and fundamental defects in the material gallium oxide. This is a material with high potential future impact as a material for power electronics. There are two key benefits: (i) the ability to withstand high electric fields, without electrical breakdown and (ii) the ability to operate under higher temperatures. The improved ability to withstand electric fields, opens the possibility to reduce the thickness of the active material, which in turn will reduce the dissipation of heat. However, to realize these possibilities it is critical to improve the knowledge of this material. As part of previous work in our group at the University of Oslo, we have managed to identify a class of so-called bi-stable defects. Point defects can originate from a missing atom, an additional atom or merely atoms sitting in the wrong position, in an otherwise perfect lattice. In order to understand and hopefully be able to control these defects we will employ a range of state-of-the-art modelling and experimental techniques. Since the start in February 2021, one researcher (start 01.02.2021) and one PhD (start 01.08.2021) have been employed in the project. One master student which has been connected to the project has submitted his thesis. Within this period the focus has been on understanding hydrogen in gallium oxide, the bi-stable defect E2* and we have started the work on diffusion of Sn and Zn. We have also conducted a mini-seminar in collaboration with the RCN funded projects FUNCTION and GO2DEVICE with 12 attendees.

Metal oxide semiconductors are widely recognized as prime materials for future energy technology. While being abundant and environmentally friendly, they exhibit a diverse set of functional properties, making them attractive for applications in several different fields, e.g., photovoltaics, LEDs, fuel cells, batteries, photocatalysis and power electronics. However, all of those applications require control over the defect population, which has proven to be challenging for this materials system. A specific class of defects with strong electron-phonon interaction have proven to be especially challenging, and have previously not been possible to describe with standard density functional calculations. They are also challenging to identify from an experimental view, i.e., by optical and electrical techniques, due to large Franck-Condon shifts and vibrational broadening. Thus, there is an imminent knowledge need for a fundamental understanding of this class of defects. Since 2016 there has been a rapid development on hybrid density functional calculations at UiO together with international collaborators. Combined with the long track record of defect identification with optical and junction spectroscopy techniques. We believe we are in a unique position to closely integrate defect modeling with experimental identification in metal oxides in general. In GO-POW we target one specific material Ga2O3, which has shown very promising properties as a material for power electronics. Bi-stable defects in Ga2O3 may, however, severely limit the performance. The material is highly an-isotropic and thus introduce additional challenges, compared to materials like Si, ZnO and SiC. However, equipped with state-of-the-art methodology both on the modelling and experimental side, we are confident that addressing this challenge is both timely and possible. It is also of imminent technological need, since Ga2O3 is expected to mature to the level of industrial applicatoin already in 2035.