Photothyristor

1,161,269. Semi-conductor devices; lasers. WESTINGHOUSE ELECTRIC CORP. 4 Oct., 1967 [10 Oct., 1966]. No. 45177/67. Headings H1G and H1K. [Also in Division G2] A PNPN semi-conductor controlled rectifier comprises a semi-conductor wafer 10 having two base regions of the P-type 16 and N-type 14 sandwiched between two emitter regions of the P-type 12 and N-type 18 to define three PN junctions; anode 28 and cathode 33 at the major surfaces of the wafer 10 in non-rectifying contact with the emitter regions; and a light energy pipe 40 optically coupled to the N-type emitter region to conduct light pulses from a light source and direct them upon the emitter 18 so that after passing through the emitter they generate electron-hole pairs at least in the adjacent P-type base 16. The semi-conductor wafer is made of silicon and the N-type emitter 18 has a thickness of the order of 10-3 cm. The light pulses have a wavelength of 8500 Angstrom units and are produced by one or more gallium arsenide laser diode assemblies immersed in liquid nitrogen and mounted directly on the fibre-optic light pipe face. Where a number of controlled rectifiers are to be fired simultaneously this light pipe comprises a main pipe system, Fig. 6, divided at the end farthest from the lasers into a plurality of smaller diameter pipes 62, 64, 66 connected to respective controlled rectifiers. These smaller pipes are each made up of a number of individual, randomly assembled fibres 68 to ensure that the light is split equally amongst them to give equal light energy at each rectifier.