Bias-dependent radiation damage in high-resistivity silicon diodes irradiated with heavy charged particles

High-resistivity p+–n–n+ planar diodes were irradiated with neutrons to fluences up to 2×1014 cm−2 1 MeV neutron NIEL equivalent and with pions to 0.47×1014 cm−2. Special care was taken to irradiate samples under strictly controlled conditions (temperature, bias). The influence of detector biasing on the effective dopant concentration as measured with the C–V method was studied. Permanently biased diodes exhibit about two times higher |Neff| after beneficial annealing has been completed. After switching off the bias the difference between biased and unbiased samples diminishes with a temperature-dependent annealing time. Part of the difference is attributed to a bistable defect since it recovers if the bias is re-applied for a few days at room temperature. The bias-induced damage was estimated to result in a 40–70 V addition to required bias for detectors in the ATLAS SCT after 10 years of LHC operation.