Waveguide Mode Formation as a Potential Cause of Switch Failure in High-Power Wide-Bandgap Photoconductive Switches

The integration of photoconductive semiconductor switches (PCSSs) into pulsed power systems may have improvements over conventional switching, but failure modes occurring near the illuminated edge of PCSS devices between switching operations present a serious limiting factor. While these failure modes have previously been difficult to characterize, this paper proposes a theory for a potential contributing source of failure supported by observations derived from the results of an FDTD simulation on an optically excited semiconductor switch. A computational analysis combining both solid-state and electromagnetic physical models reveals what appears to be an unintentional waveguide-like behavior in the optically excited plasma-filled PCSS device in strong agreement with the documented observations in the experiment. The net effect of nonuniform charge carrier generation as a result of waveguide-like mode formation is theoretically assessed, and the additional areas of investigation into this pivotal problem area in the PCSS design are suggested.