Gate turn-off thyristor

Claim 1

In a gate turn-off thyristor device including: a semiconductor body having three zones of alternatingly opposite conductivity type between the major surfaces thereof which constitute the control base, main base and counter-emitter zones respectively of a gate turn-off thyristor, and an emitter zone of a conductivity type opposite that of said control base zone formed in said control base zone at one of said major surfaces; said control base, main base and counter emitter zones of said semiconductor body being each divided into first and second regions with said emitter zone being in said first region of said control base zone, whereby said emitter zone and said first regions of each of said control base, main base and counter-emitter zones constitute a main gate turn-off thyristor; a further emitter zone of a conductivity type opposite that of said control base zone formed in said second region of said control base zone at said one major surface, whereby said further emitter zone and said second regions of each of said control base, main base and counter-emitter zones constitute an auxiliary gate turn-off thyristor; a common ohmic contact for said first and second regions of said counter-emitter zone; a respective ohmic contact on said one major surface for each of said first region of said control base zone, said second region of said control base zone, said emitter zone and said further emitter zone; and conductive means connecting said contact for said first region of said control base zone to said contact for said further emitter zone, whereby said contact for said first region of said control base zone and said common contact for both regions of said counter-emitter zone constitute the load current terminals of said thyristor device and said ohmic contact for said second region of said control base zone constitutes the control current input terminal of said thyristor device for turning same on and off; the improvement wherein: said first and second regions of at least one of said zones of said semiconductor body are differently doped to cause said auxiliary thyristor to have a turn-off gain and a holding current which are sufficiently less than the turn-off gain and the holding current respectively of said main thyristor so that said auxiliary thyristor will remain conducting during the current conducting switched-on state of said main thyristor and continuously feed a control current to said control electrode of said main thyristor to reduce the forward voltage drop of said main thyristor whereby the on-state behavior of said semiconductor switch is improved and the holding current of said semiconductor switch is reduced.