GaAs—Si photon-activated switch

A light-activated low-level switch (LAS) has been developed for multiplexing applications. The switch consists of an electroluminescent GaAs p-n 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 multiplexers. A general design theory based on the Ebers & Moll [1] low-level transistor model 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.