Type inversion in silicon detectors

Silicon strip detectors and photodiodes were irradiated in an 800 MeV proton beam. The change of the effective doping concentration was monitored by measuring diode C- V curves. Type inversion is observed at a fluence Φ = 1.5 × 10 13 cm −2. Further evidence for type inversion is obtained from a study of pulses generated by an infrared LED in silicon strip detectors. A two-level parametrization is used to describe donor removal and acceptor state creation during proton irradiation: N eff = N 0 exp(− cφ)− βφ . We measure values of c = (5.5 ± 1.1) × 10 14 cm 2 and β = (0.031 ± 0.006) cm −1. After type inversion the depletion voltage increases with proton fluence. This may set the limit for the lifetime of silicon detectors at future colliders. However, the occurence of type inversion does not degrade the performance of silicon strip detectors. The effective doping concentration showed a complex post irradiation behaviour. After a short term annealing period the doping concentration increased beyond the value that had been reached immediately after the exposure.