WIDE-BANDGAP PHOTODIODES FOR SCINTILLATOR READOUT

THE PURPOSE OF THIS PHASE I PROJECT IS TO MAKE PHOTODIODES FROM WIDE-BANDGAP III TO V MATERIALS FOR USE WITH SCINTILLATORS IN RADIATION DETECTION SYSTEMS. THE MATERIAL TO BE INVESTIGATED IS GALLIUM INDIUM PHOSPHIDE, GA.52IN.48P,WHICH HAS A BANDGAP OF 1.9 EV AND IS LATTICE-MATCHED TO GALLIUM ARSENIDE. THE PHOTODIODE DARK CURRENT, WHICH LIMITSTHE SIGNAL-TO-NOISE RATIO AND THE ENERGY RESOLUTION OF SYSTEMS USING SILICON PHOTODIODES, WILL BE GREATLY REDUCED BY USING A WIDE-BANDGAP MATERIAL. THE MATERIAL IS BEING GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION AND PROCESSED INTO-PROTOTYPE DETECTORS. THE PROTOTYPE PHOTODIODES ARE TESTED ELECTRICALLY AND OPTICALLY. THESE PHOTODIODES, IF THE TESTS ARE SUCCESSFUL, COULD BE USED TO REPLACE PHOTOMULTIPLIERS IN SEVERAL NUCLEAR AND HIGH ENERGY PHYSICS APPLICATIONS IN WHICH PHOTOMULTIPLIER TUBES ARE LESSTHAN IDEAL. PHOTOMULTIPLIERS, AS VACUUM TUBE DEVICES, SUFFER FROM A VARIETY OF DISADVANTAGES, INCLUDING RELATIVELYLARGE VOLUME, HIGH VOLTAGE REQUIREMENTS, LOW QUANTUM EFFICIENCY, SENSITIVITY TO MAGNETIC FIELDS, AND INSTABILITY. A PHOTODIODE SYSTEM WOULD ALLOW OPERATION COMPLETELY IN THE SOLID-STATE.