Development and efficiency of high voltage Silicon carbide photoconductive semiconductor switches
Sullivan, William W.
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High voltage photoconductive semiconductor switches (PCSSs) offer many performance benefits over switches typically used in pulsed power and power modulator applications including lower timing jitter, optical trigger isolation, tens to hundreds of MHz repetition rates, long device lifetimes, and compact geometries for reduced space requirements. This dissertation focuses on the development and efficiency of PCSSs fabricated out of silicon carbide for megawatt level switching applications and includes all aspects of device work including device design, modeling, fabrication, testing, and evaluation. Multiple lateral and vertical PCSSs were simulated, fabricated, and tested and the results were used to aid in future device designs. High energy electron beam irradiation was used to increase the blocking voltage of the PCSSs by a factor of ≥7 and a post-irradiation anneal was used to increase the efficiency by a factor of at least 3.5. Current-voltage measurements, thermally stimulated current spectroscopy measurements, microwave photoconductivity decay measurements, and Silvaco simulations were used to understand trapping and its effects on device operation. Sub-contact epitaxial layer doping was used as a means to eliminate material cracking when switching moderate currents at 10 kV to improve device lifetime and further improvements to the device's photocurrent efficiency are discussed.