Avalanche injection in high-speed thyristors

The aim of the present paper is to show the possibility of designing high-power semiconductor switches the turn-on time of which is as short as that of hydrogen thyratrons. These devices switch pulses of 10⁵W with turn-on times in the nanosecond range. In the OFF state all the voltage applied to a semiconductor switch is concentrated on the space-charge region (SCR) where there are assumed to be no free carriers. The process of switching into the ON state in a conventional thyristor switching mechanism is to fill the SCR with free electrons and holes injected from emitters by diffusion through base regions. The generation of carriers due to impact ionization in the SCR during the whole transition process accelerates switching. The avalanche injection (AI) suggested by Gunn [1] in diodes is the process providing impact ionization despite the voltage decrease in the device during its switching. At first we consider simplified AI processes and their potentialities in three-layer structures. Then the results are extended to more complex four- and five-layer structures by including the gate current. At the end the experimental data are given.