Diamonds are no longer exclusively for jewelry: photoconductive diamond switches

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When it comes to the semiconductor industry, silicon has reigned as king of electronics, but it is hitting its physical limits.

Scientists at Lawrence Livermore National Laboratory (LLNL) are turning to diamond as an ultra-wide bandgap semiconductor to more efficiently power the electric grid, locomotives and even electric cars.

It has been shown that Diamond has superior carrier mobility, a powerful electric field and high thermal conductivity – main characteristics for electronic device control.

After the creation of a chemical vapor deposition (CVD) process, it became especially desirable to grow high-quality single crystals.

The team investigated the properties of such diamonds produced synthetically, which are of higher quality than those that occur naturally. LLNL physicist Paulius Grivickas, lead author of a paper in Applied Physics Letters, said, “In electronics, you want to start from the purest possible material so you can shape it into a device with the desired properties,”

The best combination of conductivity and frequency response is achieved in photoconductive devices by introducing impurities which control the lifetime of the recombination of the carrier. The researchers found that electron irradiation is a cheap and easy alternative to this method in diamond, which produces recombination defects by knocking out of place lattice atoms.

“We said to ourselves ‘let’s take this pure, high-quality CVD diamond and irradiate it to see if we can match the carrier lifetime,'” Grivackas said. “Eventually, we figured out which irradiation defect is responsible for the carrier lifetime and how the defect behaves during annealing at technologically relevant temperatures.”

For instance, in the power grid, photoconductive diamond switches made in this way can be used to monitor current and voltage spikes that can burn out equipment.

Current silicon switches are big and voluminous, but with a system that could fit on a fingertip, the diamond-based switches will do the same thing, Grivickas said.

The analysis also involves applications in power distribution systems, where the team demonstrated the possibility of high-frequency megawatt-class power generation, which requires optimizing the diamond’s high-frequency conduct.

Lars Voss and Adam Conway, engineers from Livermore, as well as researchers from the University of Vilnius in Lithuania, the State University of Belarus and the National Academy of Sciences in Belarus, collaborated on this work.

“Reference: “Carrier recombination and diffusion after electron irradiation and annealing of high-purity diamonds” by P. P. Ščajev, Grivickas, N. S. Lastovskii, Kazuchits, L.

F. Voss and A. M.

A. Mazanik, Conway, O. Korolik, V.

Applied Physics Letters, Bikbajevas, and V. Grivickas, December 14, 2020. DOI: 10.1063/5.0028363.
The study was funded by LLNL’s Laboratory Directed Research and Development program.

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