Engineers at Lawrence Livermore National Laboratory (LLNL) have designed a new type of laser-driven semiconductor switch that can theoretically achieve higher speeds at higher voltages than existing photoconductive devices. The development of such a device could allow next-generation satellite communication systems to transfer more data at a faster rate and over longer distances, according to the research team.
Scientists at LLNL and the University of Illinois Urbana-Champaign (UIUC) reported on the design and simulation of the new photoconductive device in an article published in the Electron Devices Society IEEE Journal. The device uses a high power laser to generate a charge cloud of electrons in the base material, gallium nitride, under extreme electric fields.
Unlike normal semiconductors, in which electrons move faster as the applied electric field increases, gallium nitride expresses a phenomenon called negative differential mobility, where the generated electron cloud does not disperse, but actually slows down. at the front of the cloud. This allows the device to create extremely fast pulses and high-voltage signals at frequencies approaching one terahertz when exposed to electromagnetic radiation, the researchers said.
“The aim of this project is to build a device that is significantly more powerful than existing technology, but which can also operate at very high frequencies,” said Lars Voss, LLNL engineer and principal investigator of the project. “It works in a single mode, where the output pulse can actually be shorter than the laser input pulse, almost like a compression device. You can compress an optical input into an electrical output, which allows you to potentially generate very high speed, very high power radio frequency waveforms.
If the photoconductive switch modeled in the paper could be realized, it could be miniaturized and incorporated into satellites to enable communication systems beyond 5G, potentially transferring more data at a faster rate and over longer distances. , said Voss.
High power and high frequency technologies are one of the last areas where semiconductor devices have yet to replace vacuum tubes, Voss added. Newer compact semiconductor technologies capable of operating at over 300 gigahertz (GHz) while delivering one watt or more of output power are in high demand for such applications, and although some high electronic mobility transistors can achieve high electronic mobility. frequencies above 300 GHz, they are generally limited in power generation, the researchers reported.
“The modeling and simulation of this new switch will provide guidance for experiments, reduce the costs of test structures, improve the lead time and pass rate of laboratory tests by preventing trial and error, and allow correct interpretation of test results. experimental data, “said lead author Shaloo Rakheja, an assistant professor in the Department of Electrical and Computer Engineering and resident professor at the Holonyak Micro and Nanotechnology Laboratory at UIUC.
Researchers are building the switches at LLNL and exploring other materials such as gallium arsenide to optimize performance.
“Gallium arsenide expresses negative differential mobility at lower electric fields than gallium nitride, so it is an excellent model for understanding the tradeoffs of effect with more accessible tests,” said Karen Dowling, LLNL postdoctoral researcher and co-author.
Reference: “Design and Simulation of Near-Terahertz GaN Photoconductive Switches – Operation in Negative Differential Mobility Regime and Pulse Compression” by Shaloo Rakheja; Kexin Li; Karen M. Dowling; Adam M. Conway and Lars F. Voss, May 5, 2021, Electron Devices Society IEEE Journal.
DOI: 10.1109 / JEDS.2021.3077761
Funded by the laboratory-led research and development program, the project aims to demonstrate a conduction device that can operate at 100 GHz and high power. Future work will examine the impact of laser heating on the electronic charge cloud, as well as improving understanding of how the device works in an electrical-optical simulation setting, the team reported.
The simulation work was carried out by lead author Rakheja and Kexin Li at UIUC. The original principal investigator of the project, Adam Conway, formerly of LLNL, also contributed.