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Laser-Driven Semiconductor Switch Pushes Speed Capabilities of Next-Generation Communications

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LIVERMORE, Calif., June 23, 2021 — A laser-driven semiconductor switch design can theoretically achieve speeds and voltages higher than existing photoconductive devices — potentially enabling communication speeds beyond 5G if the switch were to be miniaturized and incorporated into satellites. The technology was conceived through a joint research effort between Lawrence Livermore National Laboratory (LLNL) and the University of Illinois Urbana-Champaign (UIUC). The research team’s device uses a high-powered laser to generate an electron charge cloud in the base material gallium nitride while under extreme electric fields.
Diagram representing the operating principles behind the new semiconductor switch. Courtesy of Lawrence Livermore National Laboratory.
Diagram representing the operating principles behind the new semiconductor switch. Courtesy of Lawrence Livermore National Laboratory.

Unlike normal semiconductors in which electrons move faster as the applied electrical field is increased, gallium nitride expresses a phenomenon called negative differential mobility, where the generated electron cloud slows down at the front of the cloud. This allowed the device to create extremely fast pulses and high-voltage signals at frequencies approaching 1 THz when exposed to electromagnetic radiation, researchers said.

“The goal of this project is to build a device that is significantly more powerful than existing technology but also can operate at very high frequencies,” said LLNL engineer and project principal investigator Lars Voss. “It works in a unique mode, where the output pulse can actually be shorter in time than the input pulse of the laser — almost like a compression device. You can compress an optical input into an electrical output, so it lets you potentially generate extremely high-speed and very high-power radio frequency waveforms.”

If the switch described in the paper can be realized, it could indeed be miniaturized and incorporated into satellites to enable communications systems beyond 5G. This would potentially transfer more data, at a faster rate and over long distances, Voss said. High-power and high-frequency technologies, he added, are among the last areas where solid-state devices have yet to replace vacuum tubes. New compact semiconductor technologies capable of more than 300 GHz while delivering a watt or more in output power are in high demand for such applications. While some high electron mobility transistors are able to reach frequencies higher than 300 GHz, they are usually limited in energy output, the researchers reported.

“Modeling and simulation of this new switch will provide guidance to experiments, reduce costs of test structures, improve the turnaround and success rate of laboratory tests by preventing trial and error, and enable correct interpretation of experimental data,” said Shaloo Rakheja, assistant professor in the department of electrical and computer engineering at UIUC and lead author of the paper.

The team is working to build the switches at LNN. It is also exploring other materials, such as gallium arsenide, to optimize performance.

“Gallium arsenide expresses the negative differential mobility at lower electric fields than gallium nitride, so it’s a great model to understand the trade-offs of the effect with more accessible testing,” said Karen Dowling, a postdoctoral researcher at LLNL and a co-author of the paper.

The project was funded by the Laboratory Directed Research and Development program with the goal of demonstrating a conduction device capable of operation at 100 GHz and at a higher power. Future work will examine the impact of heating from the laser on the electron charge cloud, as well as improving the understanding of the device’s operation under an electrical-optical simulation framework, the team reported.

The research was published in IEEE Journal of the Electron Devices Society (www.doi.org/10.1109/JEDS.2021.3077761).

Photonics.com
Jun 2021
Research & Technologylasersswitchphotoconductivesatellitesatellite communications5G6GLawrence LivermoreLawrence Livermore National LabLawrence Livermore National LaboratoryUniversity of Illinois at Urbana-ChampaignUniversity of IllinoisIEEEIEEE Journal of the Electron Devices Society

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