Mechanism of p-n junction breakdown at high reverse voltage ramps

It is shown that flat tunneling-assisted impact ionization fronts in p-n junctions operating at a high buildup rate (ramp) u of the reverse voltage can be obtained provided that the rate g f of the tunneling generation of electron-hole pairs is much greater than the impact ionization rate g i in the initial stage of breakdown. Usually (e.g., in silicon) g f ≪ g i and, therefore, the multiplication of the first hundreds of electron-hole pairs due to the impact ionization leads to the avalanche-streamer transition much before the overlap of avalanches. In this case, the diode transition to the conducting state may be caused by the interelectrode gap shortage by a large number of streamers, the total resistance of which can be much smaller than the load resistance. A simple model of such a “multistreamer” breakdown is proposed according to which the switching time is virtually independent of the streamer parameters and is inversely proportional to u . The diode resistance in the conducting state significantly drops with increasing ramp u and grows with increasing velocity of streamers.