Lawrence Livermore National Laboratory has demonstrated the feasibility of megawatt class radio frequency (RF) power generation using wide bandgap silicon carbide (SiC) photo conductive semiconductor switches (PCSS) driven by a modulated laser. However, widespread adoption of the technology has been limited by the large size of the laser relative to the size of the switch due to the low fraction of incident light absorbed within the semiconducting material.
Our study sought solutions to reduce the drive laser size by utilizing a new architecture—the total internal reflection switch (TIRS)—and improving the overall efficiency of linear photoconductive switches under development. Second, we examined the feasibility of using diamond (instead of SiC) and sub-band gap illumination for direct generation of GHz RF to provide an additional reduction in switch volume and reduce total laser power requirements based on diamond's superior transport, voltage handling, and thermal properties. This work demonstrated substantial enhancement in responsivity compared to the traditional axial design and a pathway to greater than 1000x total enhancement in device responsivity at the same applied fields. Several grades of diamond were characterized and tested, and we found the nitrogen-doped diamond to be appropriate for sub-band gap illumination and a strong candidate for next generation PCSS systems.
This study expands Livermore's core competency in lasers and optical science and technology and supports the Laboratory's mission to deliver scientific discoveries that solve pressing national security challenges. The work has generated interest for defense applications and, potentially, follow-on sponsored research.
Bora, M., et al. 2019. "A total internal reflection photoconductive switch." IEEE Electron Device Lett., vol. 40, no. 5, pp. 734-737, May 2019. doi: 10.1109/led.2019.2903926. LLNL-JRNL764480.
Grivickas, P., et al. 2018. "Recombination mechanisms and photoconductive switching in V-doped SiC." Poster, 12th European Conference on Silicon Carbide and Related Materials, Birmingham, UK, September 2018. LLNL-POST-757299.
——— . 2019."Intrinsic shape of free carrier absorption spectra in 4H-SiC." J. Appl. Phys., vol. 125, no. 22, pp. 225701, doi: 10.1063/1.5095161. LLNL-JRNL-761383.
Hall, D., et al. 2018. "Carrier dynamics in diamond photoconductive switches." Poster TU.P.BP6, 12th European Conference on Silicon Carbide and Related Materials, Birmingham, UK, September 2018. LLNL-POST-757278.
——— . 2019. "Sub-bandgap triggering of diamond photoconductive switches." Oral O6A.2, 30th International Conference on Diamond and Carbon Materials, Seville, Spain, September 2019. LLNL-PRES-788717.
——— . 2019. "Maskless random antireflective nanotexturing of single crystal SiC." J. Vac. Sci. Technol. B., vol. 37, no. 4, pp. 040406–1-4, July 2019. doi: 10.1116/1.5108513. LLNL-JRNL-772753.
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