Bulk radiation damage in silicon detectors and implications for LHC experiments

Bulk radiation damage to high resistivity n-type silicon detectors was studied with incident π+ (190 MeV) and protons (500, 647 or 800 MeV). Silicon bulk damage constants were extracted based on proton fluences, Φ, up to ∼8 × 1013 cm−2 and for π+ fluences up to ∼3 × 1013 cm−2. Although the measured damage constants for π+ and for proton irradiations were different, a simple empirical relationship was proposed to relate the π+ and proton radiation damage data. In addition: (a) Activation time constants for reverse annealing were determined at four temperatures between 0°C and 50°C. (b) 8 silicon detectors were exposed to a second proton fluence of ∼3 × 1013 cm−2. The resulting changes in the effective dopant concentration, Neff, were consistent with a model where the bulk radiation effects were purely additive. (c) Following reverse annealing the bulk radiation damage to high resistivity n-type silicon detectors was consistent with the simple functional form: Neff(Φ) = Neff(0)e−cΦ − (gc + gY)Φ, with c, gc and gY damage coefficients measured for π+ and proton radiation. The measured damage coefficients were used to provide predictions for the depletion voltage for the innermost pixel and silicon strip layers in the large detectors at the LHC.