Integratable differential light detector

Claim 1

A three-terminal semiconductor device which can transform the magnitude of the difference of intensities of two input light beams into a corresponding electrical output signal, comprising first and second photo diodes having a common semiconductor substrate, wherein each of said diodes includes at least an N-doped region and a P-doped region, the first diode having a first ohmic contact formed on a surface of its P-doped region, the second diode having a second ohmic contact formed on a surface of its N-doped region, a connecting intrinsic or near intrinsic region between a surface of the N-doped region of the first diode and a surface of the P-doped region of the second diode, and a third ohmic contact formed to the connecting region; said ohmic contacts being connected to respective terminals for connecting the device to a direct-current power supply having negative, positive and intermediate potential terminals, with the first contact connected to the negative terminal, the second contact to the positive terminal, and the third contact via current sensing means to the intermediate potential terminal; the device being operative with the two light beams directed respectively to the first and second photo diodes resulting in the production and collection of electrons from the detection of an intensity of one light beam and the production and collection of holes from the detection of the intensity of the other light beam, with the connected or integrated semiconductor allowing the recombination of electrons and holes, the excess number of electrons or holes, depending upon which light beam is received with the greatest intensity, being extracted from the recombination region and detected by the current sensing means to produce an output signal indicative of the difference of intensity of the two light beams.