SEMICONDUCTOR SWITCHING DEVICE

... 1,211,745. Semi-conductor controlled rectifiers. GENERAL ELECTRIC CO. 27 Nov., 1967 [19 Dec., 19661, No. 53971/67. Heading H1K. In a PNPN switching device one of the outermost zones consists of a main region to which the anode or cathode is ohmically connected and an auxiliary region carrying a non-ohmic gate contactor having an area arranged for exposure to a controllable illumination source, the construction being such that the resistance between the gate contact or area and the anode or cathode is higher than that of any current path of the same length in the main region. This accelerates the spread of current of firing thus reducing the turn on delay and rise times and is achieved either by making the auxiliary region thinner or by isolating it from the main region. Where a thinned region is used may be circular and disposed, preferably centrally, within the main region or segmental or annular and disposed at or near the edge of the main region, or there may be plurality of regions ...