GaAs-Si photon-activated switch

A light-activated low-level switch has been developed for multiplexing applications. The switch consists of an electroluminescent GaAs PN diode and a double emitter silicon transistor. (Both NPN and PNP units have been made.) The two (light emitter and detector) are coupled optically. The switch is a substantial improvement over existing switching devices used in multiplexors. A general design theory based on Ebers & Moll's paper is given with special emphasis on breakdown voltage, "ON" impedance, offset voltage, and switching speed. It is shown how the design considerations lead to a specific geometry for the detector. Results of extensive testing are reported. The devices operating with a 100 mw diode input showed the following characteristics: NPN PNP BVEE20-25 v 30-40 v REE10-15 \Omega <100 \OmegaVo<50 µv <50 µv ton{RL=10K} {RL=1M} < 3 µsec < 3µsec toff{RL=10K} <10 µsec <10 µsec {RL=1M} <150 µsec <150 µsec