Destruction behavior of power diodes beyond the SOA limit

Simulation results show how cathode-side filaments may trigger a thermal runaway at the end of a reverse-recovery period of diodes turned off with extremely high current rates. The mechanism is not essentially affected by the edge termination if an appropriate design is chosen. While multiple avalanche-induced filaments may appear during the reverse-recovery period, at the end of the turn-off phase a single “winning” filament carries the total current. This can result in a local melting of the diode. The appearance of a cathode-side filament by itself does not necessarily lead to the diode destruction. However, a high thermal carrier generation rate can result in an uncontrollable increase of the current density in a single filament connecting the anode and the cathode contact. It is shown t hat the reverse-recovery charge as a function of the dc-link voltage shows a characteristic super-linear increase below the critical value dc-link voltage at which the diode current increases uncontrollably.