High-field fast-risetime pulse failures in 4H- and 6H-SiC pn junction diodes

We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3x10(17) cm(-3)) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to de breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.