ELECTRICAL-PROPERTIES AND CHARGE COLLECTION EFFICIENCY FOR NEUTRON-IRRADIATED P-TYPE AND N-TYPE SILICON DETECTORS

Ion-implanted n-type and p-type detectors have been irradiated with neutrons of approximately 1 MeV up to a fluence of 10(14) cm-2. From I-V and C-V measurements the reverse current and the full depletion voltage have been determined at successive levels of neutron fluence. The effective doping concentration versus fluence and the reverse current damage coefficient are presented. Room temperature annealing after the irradiation is discussed. At successive levels of neutron fluence, the shape of the current pulse induced by relativistic electrons and alpha particles has been studied using a fast current amplifier. For a detector irradiated up to 1.1 10(14) n cm-2 and biased at approximately 20% above the depletion voltage, the charge collection deficit for approximately 2 MeV electrons is < 20% for an integration time of 15 ns. For alpha particles the current pulse is different for front and rear side incidence and its shape changes with neutron fluence. This shape is related to the electric field inside the detector and therefore provides another way to determine the neutron-induced effective impurity concentration.