Avalanche photodiodes that have large area (currently 17mm active-area diameter but potentially up to 75 mm), uniform highgain, and low noise, when combined with a high voltage vacuumphotodiode "front end," make possible a hybrid photodetector thatcombines the strengths of photomultipliers and solid-statephotodetectors. The hybrid has the photo response of aconventional photomultiplier. It can have the extremely low darkcurrent of an S-20 photocathode, or it can have a tailored spectralresponse, such as a solar-blind ultraviolet response. At the sametime, the hybrid has many of the advantages of solid-statephotodetectors, such as simplicity, compactness, ruggedness, verylarge dynamic range, and freedom from afterpulsing. In aproximity-focused version, the hybrid offers insensitivity toexternal magnetic fields, while in an internally processed versionit offers the potential for extremely low cost. In certainrespects, such as its nearly ideal excess noise factor, itoutperforms either kind of photodetector. The hybrid is a candidate to replace photomultipliers in the readout of largecalorimeters in future high energy physics detectors at theSuperconducting Super Collider (SSC) and elsewhere. The objectiveof Phase I is to demonstrate the fast response and low excess noisecharacteristics of the hybrid photodetector. The Phase IIobjective is to resolve all technical issues and demonstrateprototypes ready for commercial manufacture.Anticipated Results/Potential Commercial Applications as described by the awardee:For SSC, the hybrid, with a solar-blindphotocathode, could be adopted as the photodetector of choice forreadout of a barium fluoride calorimeter; with a green-sensitivephotocathode, the hybrid could be used to read out alead/scintillating tile calorimeter. In the commercial market, alow cost version may replace photomultipliers in a wide range ofapplications. In defense applications, (such as opticalcommunications or laser radars) the nearly ideal excess noisefactor could lead to improved cost-performance of entire systems.
