Performance evaluation of picosecond high-voltage power switches based on propagation of superfast impact ionization fronts in SiC structures

We employ a simple analytical model of superfast impact ionization front in a reversely biased p⁺-n-n⁺ structure to evaluate the performance of prospective 4H-SiC closing switches based on propagation of ionization fronts. The model allows to relate the order of magnitude values of the front velocity and the electron-hole plasma concentration behind the front to the basic material and structural parameters. We show that high avalanche breakdown field and impact ionization rate of the wide-band-gap 4H-SiC lead to dramatic improvement of switching characteristics with respect to Si structures currently used in pulse power applications. The concentration of electron-hole plasma generated by the front passage is of the order of 10¹⁸ versus 10¹⁶ cm^-3 in Si. The velocity of ionization front in 4H-SiC is several times larger than in Si. Finally, we discuss possible triggering mechanisms for the ionization front in SiC.