Investigation of Optically Initiated Avalanche Silicon Carbide High Power Switches

The non-linear, optically initiated closure of semi- insulating Gallium Arsenide (GaAs) high voltage switches results in filamentary conduction. The conduction current magnitude and the conduction current pulse length are limited by the damage of the switch electrodes and bulk GaAs material. Heavily doped regions under the Ohmic contact have been investigated for the purpose of spreading the current filament density over a larger spatial region to reduce contact metallization damage. However, the product of peak current capability and conduction time is limited by the number of filaments initiated. Therefore, an alternate semi-insulating material, specifically Silicon Carbide (SiC), was considered. This paper investigates and compares the parameters of GaAs and SiC that are predominant in optically initiated avalanche switches. SiC has a much large dielectric strength than GaAs, but the electron mobility is much lower. In addition, the SiC does not exhibit the negative differential mobility of GaAs. This paper reports on the results of a modeling exercise that investigates the optically initiated closure of semi-insulating GaAs button switches and semi-insulating, compensated SiC button switches. A commercially available semiconductor physics modeling code from Silvacotrade was used to model the optically initiated closure phenomena and filamentary conduction in GaAs. The GaAs code was calibrated to the peak currents observed in experiments. Similar switch models were developed for semi-insulating SiC switches. The behavior of SiC predicted by the codes in optically initiated avalanche mode is presented. The possibility of "lock on" in SiC is also addressed.