Study of the voltage drop process for the case of high-power thyristors switched in the impact-ionization mode

The voltage drop process for the case of high-power thyristors switched to the conducting state by an impact-ionization wave excited by means of an overvoltage pulse with a nanosecond rise time is studied. In experiments, a voltage with a rise rate $dU/dt$ in the range of 0.5 to 6 kV/ns is applied to a thyristor with an operating voltage of 2 kV. Numerical simulation shows that the calculated and experimentally observed voltage drop times are in quantitative agreement only when the structure active area through which the switching current flows depends on $dU/dt$. The active area increases with dU/dt and with increasing initial silicon resistivity. In this case, the active area steadily approaches the total structure area at $dU/dt>$ 12 kV/ns.