GaAs PCSSs for DC applications

Abstract

As the demand for greater flexibility and increased energy density moves highly interactive components closer together in pulsed power systems, the development of technologies for less complex and more robust system designs is critical. A key system component that impacts these goals is the trigger generator (TG). Inexpensive, compact, fiber-optically controlled TGs that deliver trigger pulses with sub-nanosecond jitter have been created with photoconductive semiconductor switches (PCSSs). A further simplification in pulsed power design is to move from pulsed to DC charged components. This paper reports results from DC charged GaAs PCSSs with 0.25-1.0 cm gaps extending previously reported results on smaller devices at 3 kV to a new regime of 100 kV. High voltage GaAs PCSSS are typically pulsed charged for less than 100 ?s so that they can hold-off 60-100 kV/cm without self-triggering into high-gain (lock-on) switching or initiating surface flashover. To hold-off high fields for longer periods and extend GaAs PCSSS to DC applications, we have utilized neutron irradiated GaAs (nGaAs). Neutron irradiation in GaAs increases the defect density, shortens the carrier recombination time, and (for devices with large insulating regions) reduces the dark current, which improves DC hold-off strength. PCSS contacts in this research were created using rapid thermal annealing (RTA) to produce high adhesion and low contact resistance. However, this can reduce the defect density near the contacts by annealing some of the n-induced defects. Hence, a range of RTA temperatures and n doses were studied to understand the tradeoff space for contact adhesion and DC hold-off. This paper and another at this conference present preliminary results from I-V characterization, DC holdoff, and switching tests on GaAs and n-GaAs PCSSS. These PCSS devices were demonstrated to hold off fields of 39-61 kVDC/cm, respectively. Irradiation doses over a range of 3?10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> -1?10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> (1 MeV Si equiv.) were explored in search of optimal performance. Additionally the impact of the fabrication processes on the benefits of irradiation is explored and the observation of unusual low frequency oscillations during GaAs I-V testing is discussed.