Recent developments in the investigation of surface flashover on silicon photoconductive power switches

A limiting factor in the feasibility of photoconductive power switches is the optical energy required to trigger the switch and maintain the conduction. Since the optical energy required is proportional to the square of the length, the length of the switch should be made as short as possible. The minimum length is dictated by surface flashover which occurs at field strengths which are lower than the expected bulk breakdown. Previous experimental observations indicate that the vacuum breakdown may be initiated by thermal process occurring on the switch. Therefore this work has concentrated on investigating the transient thermal processes that may take place in the switches. Modeling of the thermal process indicates that substantial heating can occur in a low resistivity small diameter channel or thin surface layer, even for short time scales without affecting total resistance. The heating can cause outgassing which then provides material in the vacuum for breakdown to occur. Data has been taken to determine the feasibility of thermal effects as a mechanism for initiating breakdown. Innovative techniques such as the use of liquid crystals to indicate temperature and laser illumination of the contacts will be discussed. A brief description of the vacuum chamber and components as well as the electrical components will be presented. Additional measurement techniques, experimental data, and theoretical data will also be presented.