Long term damage studies using silicon detectors fabricated from different starting materials and irradiated with neutrons, protons, and pions

The long term annealing behavior of particle detectors fabricated from high resistivity float zone silicon with initial doping concentrations ranging from 0.6 × 1012 cm−3 (p-type) to 2.5 × 1012 cm−3 (n-type) was studied after exposure to fast neutrons with fluences up to 8 × 1012 cm−2. Moreover, the energy dependence of the pion displacement damage function was investigated and long term damage effects were compared for high fluence irradiations by neutrons, protons, and pions (Φ > 1013 cm−2). The effective doping concentration and the bulk generation current, taken from standard CV- and IV-measurements, were monitored in isothermal annealing procedures at 50°C. The reverse annealing of the effective doping concentration was found to be independent of the initial doping concentration. On the other hand, considerable differences were seen for the unannealing fraction. The problem of a particle and energy independent fluence normalization to equivalent 1 MeV neutron values (damage functions, NIEL hypothesis) is discussed.