Avalanche characteristics and failure mechanism of high voltage diodes

High voltage diodes made of PνN (or PπN) structures sometimes fail by second breakdown when high voltage pulses are applied. The avalanche characteristics of PνN junction diodes are analysed and it is theoretically shown that they have negative resistance regions caused by the space charge effect of the carriers. Experiments on the second breakdown are also reported and it is concluded that the current concentration induced by the negative resistance may cause diode failure.