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

Abstract

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 gf of the tunneling generation of electron-hole pairs is much greater than the impact ionization rate gi in the initial stage of breakdown. Usually (e.g., in silicon) gf≪gi 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.