With its unique features, photoconductive semiconductor switch (PCSS) is generally recognized today as a promising power electronic device. However, a major limitation of PCSS is its surprisingly low voltage threshold of surface flashover (SF). In this paper, an experimental study of surface flashover of a back-triggered PCSS is presented. The PCSSs with electrode gap of 18 mm are fabricated from liquid encapsulated czochralski (LEC) semi-insulating gallium arsenide (SI-GaAs), and they are either un-coated, or partly coated, or en- tirely coated PCSSs with high-strength transparent insulation. The SF fields of the PCSSs are measured and discussed. According to the experimental results, the high-dielectric-strength coating is efficient in both reducing the gas desorption from semiconductor and increasing the SF field: a well-designed PCSS can resist a voltage up to 20 kV under the repetition frequency of 30 Hz. The physical mechanism of the PCSS SF is analyzed, and the conclusion is made that having a channel structure, the SF is the breakdown of the contaminated dielectric layer at the semiconductor-ambient dielectric interface. The non-uniform distribution of the surface field and the gas desorption due to thermal effects of semiconductor surface currents are key factors causing the SF field reduction.
Semi-insulating gallium arsenide(GaAs) photoconductive semiconductor switches (PCSS) have great potential for high voltage switching application,however,the utility is restricted by surface flashover which would result in breakdown.In this paper,a model of photo-activated charge wave was proposed based on the theory of photo-activated charge domain(PACD) in GaAs PCSS,and moderate suppression of PACD formation by loading the semiconductor surface with dielectric material was investigated theoretically and experimentally.Current as high as 3.7 kA was obtained at 28 kV,implying that this method can effectively inhibit the surface flashover and improve the service life of DC charged GaAs PCSS.
