RADIATION DAMAGE RESISTANT SILICON FOR PARTICLE PHYSICS DETECTORS

THE USE OF SILICON (SI) RADIATION DETECTORS IN PARTICLE PHYSICS RESEARCH AND OTHER APPLICATIONS IS RESTRICTED BY THE DETECTORS' SENSITIVITY TO RADIATION DAMAGE. THIS IS PARTICULARLY TRUE FOR THE NEW GENERATION OF HIGH ENERGY COLLIDERS LIKE THE SUPERCONDUCTING SUPER COLLIDER (SSC), WHERE A HIGH INTENSITY OF NEUTRONS CREATES SERIOUS BULK DAMAGE PROBLEMS. MOST OF THE RADIATION DAMAGE RESEARCH ON THESE DETECTORS HAS FOCUSSED ON STUDIES OF IRRADIATED DEVICE BEHAVIOR IN DETECTORS MADE FROM THE SAME SOURCE OF SI AND BY SIMILAR OXIDE PASSIVATION TECHNIQUES, WITH LITTLE EFFORT TO DATE ON IMPROVING THE MATERIAL. THESE STUDIES HAVE SHOWN THAT NEUTRON BULK DAMAGE CREATES EXCESS LEAKAGE CURRENT NOISE, CHARGE TRAPPING RESULTING IN SIGNAL DETERIORATION, AND CHANGES IN COMPENSATION LEVEL THAT CHANGE THE ELECTRIC FIELD DISTRIBUTION IN THE DEVICE. THIS LAST PROBLEM IS PERHAPS THE MOST SERIOUS, PARTICULARLY FOR TRACKING DEVICES AND DRIFT CHAMBERS. CHANGES IN COMPENSATION LEVEL BY UNIFORMLY DISTRIBUTED RADIATION DAMAGE CAN AMPLIFY THE ORIGINAL FLUCTUATIONS IN COMPENSATION, THEREBY CAUSING MAJOR SPATIAL NONUNIFORMITIES IN RESISTIVITY AND ELECTRIC FIELD STRENGTH. ALUMINUM (AL) IS KNOWN TO PASSIVATE BOTH POINT AND CLUSTER DEFECTS IN SI, AND IT IS POSITED THAT AL DOPING MAY BE USEFUL FOR IMPROVING THE RADIATION HARDNESS OF SI DETECTORS. THE PHASE I RESEARCH WILL ASSESS THE FEASIBILITY OF THIS DOPING METHOD (WHICH INTRODUCES AL INTO THE POLISHED WAFERS OR FINISHED DEVICES). THESE DOPED MATERIALS ARE THEN AVAILABLE FOR PHASE II RADIATION DAMAGE STUDIES. THE SPATIAL DISTRIBUTION OF THE AL INTRODUCTION CAN BE CONTROLLED TO COUNTERACT COMPENSATION GRADIENTS IN THE STARTING MATERIAL. AL DOPING MAY ALSO GREATLY REDUCE COSTS BY ALLOWING CHEAPER STARTING MATERIAL.