Summary
Cornell engineers have made a semiconductor with a bandgap exceeding 7 electron volts and turned it into working devices, including a field-effect transistor, the Cornell Chronicle reported on 3 November 2026. The material is silicon-doped aluminum gallium oxide, described in a study published in Nature on 7 October 2026. The previous record was about 6 electron volts, a threshold that has been hard to pass because materials with wider bandgaps tend to behave more like insulators than semiconductors. “The first reaction I heard from my scientific friends was, ‘that’s impossible,’” said senior author Darrell Schlom, the Tisch University Professor in the Department of Materials Science and Engineering in the Cornell Duffield College of Engineering. “I must admit that, at first, the result did seem too good to be true.” What a bandgap is and why width matters A bandgap is the energy an electron needs to break free and carry current. The wider the gap, the harder it is to get current flowing at all, which is why very wide gap materials usually act as insulators. The payoff for crossing that line is tolerance. Semiconductors with wider bandgaps can withstand stronger electric fields before breaking down, which Cornell said makes them attractive for applications such as electric vehicles and power-grid infrastructure. Those uses are potential rather than existing ones. Achieving the record required getting electricity to flow through the material in a controllable way. Jacob Steele, Schlom’s doctoral student and lead author on the study, grew thin films of the material using suboxide molecular-beam epitaxy, a method that builds crystals one layer at a time under controlled conditions. Adding silicon atoms at a low enough temperature introduced mobile electrons to carry current. In the colossal bandgap range, defined as greater than 6 electron volts, the silicon-doped films showed room-temperature conductivity more than 100 million times higher than previously reported for materials in that category, according to the study. The AlphaFET Schlom said it was only when colleagues made the material into working devices that he judged the result “was real and potentially important for technology.” Huili Grace Xing, the William L. Quackenbush Professor, and Debdeep Jena, the David E. Burr Professor, oversaw the building of a working diode and a field-effect transistor named the AlphaFET. Jena’s doctoral student and co-lead author, Debaditya Bhattacharya, designed, fabricated and measured the device. “Making a transistor allows us to simultaneously demonstrate an essential building block of electronic systems as well as several of the semiconductor’s unique properties,” Xing said. “That includes control of conductivity over several orders of magnitude by both doping and field effect. The preliminary transistors show more than four orders of magnitude change in current modulated by the capacitively-coupled metal gate and the colossal bandgap channel.” The films were grown on sapphire. Some ultrawide-bandgap materials are difficult and expensive to make in useful sizes, while sapphire is widely available and produced at large scale. Lab hardware, not product These are laboratory devices. Jena said further work will be needed to make them practical, and described the material as a “game-changing platform.” The applications he listed are prospective. “This will enable efficient electrical propulsion systems for terrestrial and aerial vehicles, power electronics for data centers, and several new applications of interest for commercial and defense applications,” Jena said. “Colossal bandgap semiconductors will also enable telecom relevant quantum cascade lasers and vacuum UV photonic devices that have not been possible in the past.” David Muller, the Samuel B. Eckert Professor of Engineering in the School of Applied and Engineering Physics, and Naomi Pieczulewski, Ph.D. ’26, used an electron microscope to look at defects in the material. “They saw a large number of defects in this new semiconductor, akin to the state of other semiconductors at the beginning of their development, indicating that there is lots of room to further improve the properties and devices made with this semiconductor as these defects are tamed and the material can operate at its full potential,” Schlom said. The work was supported by the Air Force Research Laboratory-Cornell Center for Epitaxial Solutions and the National Science Foundation, and used the Cornell NanoScale Facility, the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials, and shared facilities at the Cornell Center for Materials Research. Sources: