Development of Photoconductive Semiconductor Switch
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4401 Dayton-Xenia Road, Dayton, OH, -
Div Dir/Prin. Research Scientist
Div Dir/Prin. Research Scientist
AbstractOBJECTIVE: Advanced pulsed power switching technologies are needed to enable future nuclear weapon effects (NWE) experimentation capabilities and concepts for the active interrogation of special nuclear materials (SNM). The objective of this research is to advance the state of the art of high-gain optically-triggered switches by increasing the current density (to>1000 A/cm) and voltage hold-off (>67 kV/cm and>100 kV total) capabilities of complete switch assemblies that allow simple laser illumination, function in oil immersion, and have rise-times and timing jitter<0.3 ns. DESCRIPTION: Traditional pulsed power systems have primarily used spark gaps in various forms as the main switches for high voltage (>100 kV) and high current (>100 kA) operations. Spark gap switches have limitations in terms of their triggering requirements, timing jitter and turn on time (both typically greater than a few nanoseconds). Photoconductive Semiconductor Switches (PCSS) are one method of switching high voltages without requiring direct electrically-connected trigger systems. PCSS have been demonstrated using silicon carbide (SiC), gallium nitride (GaN), and semi-insulating gallium arsenide (GaAs) for voltages over 100 kV with turn on times of 0.35 ns and timing jitter of ~0.1 ns. Unlike most semiconductors that only conduct as long as they are illuminated by enough light to generate current carriers, GaAs PCSS have the advantage of also being high-gain; once the device is turned on by a short laser pulse, they can remain conducting through a stable electron avalanche process. The primary issue with GaAs PCSS is that the current becomes filamentary with channel widths of ~50 micrometers and that the current per filament must be limited to<25 A for short pulses (<100 ns) in order to have long lifetimes (>107 shots). This limit is set by the localized heating of the conducting channel and the need to keep the temperature below the melting point. If bulk GaAs is uniformly illuminated, the current tends to form a few, high-current channels that can damage the switch. Illuminating with narrow lines of laser light bridging the switching gap and spaced ~300 micrometers apart has been shown to allow multiple parallel channels to form and remain separate. However, this requirement limits the overall current density and makes the laser triggering optics more complex and/or inefficient. Research in this topic areas may address : (1) The development of techniques such as"dead-bands"between channels to prevent transverse current flow and the merging of neighboring channels. It may be possible to achieve this through ion implantation or other means. If the spacing of channels can be reduced to ~100 micrometers, the current density could be tripled. (2) The development of integrated focusing lens assemblies that work under transformer oil, do not reduce the voltage hold-off, and allow more efficient use of laser light. (3) The development of advanced bulk materials and contact designs that increase voltage hold-off, switch life-time (>100,000 shots) and enhance multi-channeling with uniform illumination. (4) The development of techniques to field large parallel arrays of switches that can uniformly carry high total currents with long mean-times between failures. Impact: The development of improved optically triggered switches will enable a new class of compact, rep-rated pulsed power systems for a number DoD and other applications. A immediate application would be for a short-pulsed (~10 ns) bremsstrahlung diode driver for high-fidelity NWE experimentation and potentially for active interrogation of SNM. Other DoD applications could include: ion beam drivers for gamma ray and neutron sources; microwave sources; electron beam sources for free-electron lasers, materials processing, and chem-bio remediation. There are many potential commercial applications. PHASE I: Develop a design concept for an improved PCSS and demonstrate a small-scale prototype of a single switch capable of holding off>100 kV. A final report detailing the design and prototype results will be delivered at the end of Phase 1. PHASE II: Develop a sub-scale prototype of a PCSS system capable of holding off>100 kV DC and then of triggering a discharge of over 10 kA with a conduction time of greater than 20 ns with a timing jitter of<1 ns. A demonstration of over 106 shot life-time should be completed in Phase II. Laser energy triggering requirements should be<10 mJ. The cost per switch should be kept to less than 10 times the cost of the raw GaAs wafer material. PHASE III DUAL USE APPLICATIONS: Phase III should include partnering with a semiconductor manufacturer and/or a pulsed power system development contractor for production and fielding of the switching systems. The potential dual use applications for aircraft radars, vehicle collision avoidance systems, and ultra-wideband sensor systems should be discussed in the Phase III final report. REFERENCES: 1."Fiber-Optic Controlled PCSS Triggers for High Voltage Pulsed Power Switches", Zutavern, F.J.; Reed, K.W.; Glover, S.F.; Mar, A.; Ruebush, M.H.; Horry, M.L.; Swalby, M.E.; Alexander, J.A.; Smith, T.L.; Pulsed Power Conference, 2005 IEEE, 13-17 June 2005 Page(s):810 - 813 2."Optically Activated Switches for Low Jitter Pulsed Power Applications", Zutavern, F.J.; Armijo, J.C.; Cameron, S.M.; Denison, G.J.; Lehr, J.M.; Luk, T.S.; Mar, A.; O'Malley, M.W.; Roose, L.D.; Rudd, J.V.; Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International, Volume 1, 15-18 June 2003 Page(s):591 - 594 Vol.1 3."PCSS Lifetime Testing for Pulsed Power Applications", Saiz, T.A.; Zutavern, F.J.; Glover, S.F.; Reed, K.W.; Cich, M.J.; Mar, A.; Swalby, M.E.; Horry, M.L.; Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE, 17-22 June 2007 Page(s):189 - 189 4."A Novel Application of GaAs Photoconductive Semiconductor Switch in Triggering Spark Gap"Wei Shi; Linqing Zhang; Liqiang Tian; Lei Hou; Zheng Liu; Plasma Science, IEEE Transactions on, Volume 37, Issue 4, Part 2, April 2009 Page(s):615 - 619 5."Fiber-Optically Controlled Pulsed Power Switches", Zutavern, F.J.; Glover, S.F.; Reed, K.W.; Cich, M.J.; Mar, A.; Swalby, M.E.; Saiz, T.A.; Horry, M.L.; Gruner, F.R.; White, F.E.; Plasma Science, IEEE Transactions on, Volume 36, Issue 5, Part 3, Oct. 2008 Page(s):2533 - 2540 6."Photoconductive, Semiconductor Switch Technology for Short Pulse Electromagnetics and Lasers", Zutavern, F.J.; Loubriel, G.M.; Mar, A.; Hjalmarson, H.P.; Helgeson, W.D.; O'Malley, M.W.; Denison, G.J.; Pulsed Power Conference, 1999. Digest of Technical Papers. 12th IEEE International, Volume 1, 27-30 June 1999 Page(s):295 - 298 vol.1 7."Development and Testing of Bulk Photoconductive Switches Used for Ultra-Wideband, High-Power Microwave Generation", Burger, J.W.; Schoenberg, J.S.H.; Tyo, J.S.; Abdalla, M.D.; Ahern, S.M.; Skipper, M.C.; Buchwald, W.R.; Pulsed Power Conference, 1997. Digest of Technical Papers. 1997 11th IEEE International, Volume 2, 29 June-2 July 1997 Page(s):965 - 969 vol.2 8."3C-Silicon Carbide Photoconductive Switches", Senpeng Sheng; Xiao Tang; Spencer, M.G.; Peizhen Zhou; Wongchotigul, K.; Device Research Conference, 1996. Digest. 54th Annual, 24-26 June 1996 Page(s):190 - 191 9. Charge Transport and Persistent Conduction in High Gain Photoconductive Semiconductor Switches Used in Pulsed Power Applications, Islam, N.E.; Schamiloglu, E.; Plasma Science, 2000. ICOPS 2000. IEEE Conference Record - Abstracts. The 27th IEEE International Conference on, 4-7 June 2000 Page(s):265 10."On-State Characteristics of a High-Power Photoconductive Switch Fabricated From Compensated 6-H Silicon Carbide", Kelkar, K.S.; Islam, N.E.; Kirawanich, P.; Fessler, C.M.; Nunnally, W.C.; Plasma Science, IEEE Transactions on, Volume 36, Issue 1, Part 2, Feb. 2008 Page(s):287 - 292 11."Pulsed and DC Charged PCSS Based Trigger Generators", Glover, S.F.; Zutavern, F.J.; Swalby, M.E.; Cich, M.J.; Loubriel, G.; Mar, A.; White, F.E.; Pulsed Power Conference, 2009. PPC'09. IEEE, June 28 2009-July 2 2009 Page(s):1444 - 1447 12."Development of a Lateral, Opposed-Contact Photoconductive Semiconductor Switch", Richardson, M.A.; Stoudt, D.C.; Abdalla, M.D.; Skipper, M.C.; Schoenberg, J.S.H.; Pulsed Power Conference, 1999. Digest of Technical Papers. 12th IEEE International, Volume 1, 27-30 June 1999 Page(s):307 - 310 vol.1 13."Optically-Activated GaAs Switches For Compact Accelerators and Short Pulse Sensors", Zutavern, F.J.; Loubriel, G.M.; Helgeson, W.D.; O'Malley, M.W.; Ruebush, M.H.; Hjalmarson, H.P.; Baca, A.G.; Power Modulator Symposium, 1996., Twenty-Second International, 25-27 June 1996 Page(s):31 - 34 14."30 kV and 3 kA Semi-insulating GaAs Photoconductive Semiconductor Switch", Shi, Wei; Tian, Liqiang; Liu, Zheng; Zhang, Linqing; Zhang, Zhenzhen; Zhou, Liangji; Liu, Hongwei; Xie, Weiping; Applied Physics Letters Volume 92, Issue 4, Jan 2008 Page(s):043511 - 043511-3 15."Multi-Filament Triggering of PCSS for High Current Utilizing VCSEL Triggers", Mar, A.; Serkland, D.K.; Keeler, G.A.; Roose, L.D.; Geib, K.M.; Loubriel, G.M.; Zutavern, F.J.; Pulsed Power Plasma Science, 2007. PPPS 2007. Conference Record - Abstracts. IEEE, 17-22 June 2007 Page(s):642 - 642
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