Gate turn-off thyristor with a cathode base layer having four distinct impurity concentrations

Claim 1

In a gate turn-off thyristor having an anode A, cathode K, a first gate G 1 , a second gate G 2 and a gate current amplifying electrode arranged between the cathode and the first gate, the cathode and the second gate being arranged in a main thyristor portion MG and the first gate and the gate current amplifying electrode being arranged in an auxiliary thyristor portion AG, both the main and auxiliary thyristor portions being formed with a semiconductor device including alternately-different four PNPN semiconductor layers comprised of: (a) a first P-type layer P 1 having an anode electrode; (b) a first N-type layer N 1 adjoining said first P-type layer P 1 ; (c) a second P-type layer including: a first-impurity atom concentrations CP 2 and CP 2 ' layer P 2 both contacting said first N-type layer N 1 ; and a second-impurity atom concentration CP 2 - layer P 2 - adjoining said first-impurity atom concentration layer P 2 and under the cathode K and first and second electrodes G 1 and G 2 , said second concentration CP 2 - being of lower concentration than concentrations CP 2 and CP 2 '; and (d) a plurality of second N-type layers formed in the layer P 2 - and including a layer N 2 formed under the cathode, a layer N 3 formed under the gate current amplifying electrode, wherein said first-impurity atom concentration layer P 2 includes an impurity atom concentration CP 2 ' formed in the main thyristor portion MG having a higher impurity concentration than the impurity atom concentration CP 2 formed in the auxiliary thyristor portion AG, whereby turn-on time and turn-off time of the thyristor are both improved.