6H-SiC photoconductive switches triggered at below bandgap wavelengths

Semi-insulating silicon carbide (SiC) is an attractive material for application as high voltage, photoconductive semiconductor switches (PCSS) due to its large bandgap, high critical electric field strength, high electron saturation velocity and high thermal conductivity. The critical field strength of 300 MV/m for 6H-SiC makes it particularly attractive for compact, high voltage, fast switching applications. To realize the benefits of the high bulk electric field strength of SiC and diffuse switch current, carriers must be excited throughout the bulk of the photo switch. Photoconducting switches with opposing electrodes were fabricated on "a" plane, vanadium compensated, semi-insulating, 6H-SiC substrates. The PCSS devices were switched by optically exciting deep extrinsic levels lying within the 6H-SiC bandgap. The SiC photoswitches were tested up to a bias voltage of 11000 V with a corresponding peak current of 150 A. The 6H-SiC substrates withstood average electric fields up to 27 MV/m. Minimum PCCS dynamic resistances of 2 and 10 Ohms were obtained with 13 mJ optical pulses at 532 and 1064 nm wavelengths, respectively.