Cornell semiconductor breaks the bandgap record at more than 7 electron volts

Engineers at Cornell University have made a semiconductor with the widest bandgap yet reported, above 7 electron volts (eV), the Cornell Chronicle reported. The previous record was about 6 eV. The study was published on 7 October in Nature.

Why a wider bandgap matters

Materials with a wider bandgap can withstand stronger electric fields before breaking down, which suits high-power uses such as electric vehicles and the power grid. But the wider the bandgap, the more a material tends to behave like an insulator, which is why the 6 eV mark had been hard to pass.

Silicon added at low temperature

The material is aluminum gallium oxide doped with silicon. Lead author Jacob Steele, a doctoral student, grew thin films one crystal layer at a time with a method called suboxide molecular-beam epitaxy, adding silicon at a low enough temperature to introduce mobile electrons. Above 6 eV, its room-temperature conductivity is more than 100 million times higher than previously reported for such materials. The films grow on sapphire, which is made at large scale, while some other ultrawide-bandgap materials are hard and expensive to produce in useful sizes.

“I must admit that, at first, the result did seem too good to be true.” — Darrell Schlom, senior author, Cornell University

The team also built a diode and a field-effect transistor, called the AlphaFET. Debaditya Bhattacharya, co-lead author, designed and measured the devices, which showed more than four orders of magnitude change in current.

Many defects still to remove

The devices are preliminary. Electron microscopy by David Muller's group revealed many defects, as in other early-stage semiconductors, and the researchers said more work is needed to make the devices practical. Debdeep Jena sees future uses in electric propulsion, power electronics for data centers and ultraviolet light devices. More stories about new materials are collected under materials science.