Dispositif semi-conducteur a zones successives contigues

909,870. Semi-conductor devices, WESTERN ELECTRIC CO. Inc. May 30, 1961 [June 10, 1960], No. 19470/61. Class 37. The turn-off gain of a PNPN(NPNP) device is made large by arranging that the total α is slightly greater than unity, the α of one of the included transistors being less than but close to unity and the other greater than but close to zero. In the arrangement shown in Fig. 2, the NPN transistor is made by conventional methods to have a gain of about 0.99 but the PNP transistor is made to have a gain of about 0.05 by making the injection efficiency γ low. This is achieved in practice by making the sheet resistance of P zone 24 much higher than that of base zone 23. Actual figures are 1000 ohms/ square for the P zone and 50 ohms/square for the N zone. The device may be produced by starting with a N-type silicon base 23, the P and N zones 22, 21 being produced by successive diffusion of boron and phosphorous respectively and P region 24 is produced by phosphorous diffusion. In a further embodiment (Fig. 3) injection efficiency is reduced by causing electrode 36 to shunt most of the current from the contact 36 around the emitter junction. The resistance in the N 2 base region 33 is made large compared to the forward resistance of the emitter junction. P+ region 38 is provided to ensure that the current flowing across the junction consists primarily of holes injected into the N region 33. In the arrangement of Fig. 4, α is made low by making #, the transport factor low. This is achieved by centrally locating and reducing the area of P zone 42. Further, a pair of low resistance electrodes 46, 48 are provided so that minority carrier emission tends to accumulate in their region. Specifications 813,862, 817,905, 817,906 and 909,869 are referred to.