Avalanche breakdown in 4$H$-SiC Schottky diodes: reliability aspects

We consider problems associated with the reliability of high-power 4$H$-SiC Schottky diodes (SDs) during short-term electric overloads in the reverse direction (for diodes operating in the pulsed avalanche regime). In particular, we analyze the effect of nonuniformity of an avalanche breakdown over the diode area on the maximal avalanche energy (MAE) that can be dissipated by the diode prior to its secondary thermal breakdown. For estimating the uniformity of an avalanche breakdown, we propose that the measured pulse reverse current–voltage ( I – V ) characteristic of the diode be compared with the calculated I – V characteristic of an ideal quasi-one-dimensional diode. We measured reverse I – V characteristics of commercial 4$H$-SiC SDs: single avalanche current pulses with a duration of 1 $\mu$s were passed through the diodes; during measurements, the pulse amplitudes grew to values for which a catastrophic failure of diodes occurred. It is shown that an increase in the differential resistance of diodes on the avalanche segment of the I – V curve and a decrease in the extrapolated breakdown voltage (as compared to values calculated for ideal diodes) can lead to a decrease in the MAE.