Cornell: transistor with a record bandgap above 7 eV

Engineers at Cornell University reported a semiconductor with a bandgap exceeding 7 electron volts and built working devices from it, according to news.cornell.edu. The study was published on Oct. 7 in Nature. The material is silicon-doped aluminum gallium oxide, and the previous record was about 6 electron volts cornell.edu.

A wider bandgap lets a semiconductor withstand stronger electric fields before breakdown, which matters for electric vehicles and power-grid equipment. The difficulty is that materials with wider bandgaps tend to behave more like insulators than semiconductors cornell.edu. Senior author Darrell Schlom said the first reaction of his colleagues was "that's impossible" cornell.edu.

Growth and conductivity

Doctoral student Jacob Steele grew the thin films by suboxide molecular-beam epitaxy, a technique that builds crystalline material one layer at a time under carefully controlled conditions. Silicon atoms were incorporated at a sufficiently low temperature, which introduced mobile electrons that carry current cornell.edu.

In the range above 6 electron volts, the doped films showed room-temperature conductivity more than 100 million times higher than previously reported for materials in this category, according to the study cornell.edu. The films were grown on sapphire, a substrate that is widely available and produced at large scale cornell.edu.

Diode and AlphaFET transistor

Groups led by Huili Grace Xing and Debdeep Jena developed a diode and a field-effect transistor, named AlphaFET. Doctoral student Debaditya Bhattacharya designed, fabricated and measured the device cornell.edu. Xing said the preliminary transistors show a change in current of more than four orders of magnitude, controlled by the capacitively coupled metal gate and the channel with the colossal bandgap cornell.edu. Schlom said he became convinced the result was real only after the working devices appeared cornell.edu.

David Muller and Naomi Pieczulewski examined the material with an electron microscope and found a large number of defects. Schlom said this resembles other semiconductors at the start of their development and leaves room to improve the properties of the material and devices cornell.edu.

Jena said further work is needed to make the devices practical. He named electrical propulsion systems for vehicles, power electronics for data centers, quantum cascade lasers and vacuum UV photonic devices among possible applications cornell.edu.

Cornell builds transistor from aluminum gallium oxide with bandgap above 7 eV

Growth and conductivity

Diode and AlphaFET transistor

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