THE USE OF THE SIGNAL CURRENT PULSE SHAPE TO STUDY THE INTERNAL ELECTRIC-FIELD PROFILE AND TRAPPING EFFECTS IN NEUTRON DAMAGED SILICON DETECTORS

The induced current pulse from ionizing events occurring near contacts on each side of a p+-n-n+ silicon junction detector may be used to map the electric field present in the detector. It is of interest to define the operative effects of fast neutron-induced displacement damage in detectors destined for high radiation environments in SSC or LHC. The hole current shape, in particular, has been useful to determine that the field maximum moves to the ''rear'' n+ contact as the material apparently changes to p-type at 8 x 10(12) 1 MeV n/cm2. Trapping times for both holes and electrons have been measured as a function of neutron fluence using the current pulse width to measure charge collection time as well as using calculated charge collection times. A clear linear relationship is found for the trapping probability (1/tau) versus neutron fluence. Current pulse shapes have been calculated for representative detector fields and mobility relationships and comparison with measured shapes is reasonable.