p-n-p-n optical detectors and light-emitting diodes

Light-emitting diodes with the high-radiance Burrus configuration have been made with an internal p-n-p-n structure which causes an
S
-type negative resistance. The devices were double heterostructures using InGaAsP material. By using the proper external load impedance and bias voltage, the negative resistance can be used to obtain bistable operation with switching from low current to high current triggered by a small current (e.g., 1 μA). Light coupled into the center junction can be used as the source of signal current. Since light output is proportional to the total current, this type of device can be used as a light-signal repeater.