A model of charge collection for irradiated p+n detectors

The charge collection in irradiated p+n silicon detectors was studied as a function of the reverse bias voltage. Oxygenated and non-oxygenated devices were irradiated beyond type inversion with 24 GeV/c protons. The charge collection is successfully described with a model based on the hypothesis that the charge trapping depends on the carriers velocity. With this model, values for the full depletion voltage are extracted which show good agreement with those measured using the CV technique. The model allows a quantitative understanding of why although oxygenation of p+n devices improves substantially the full depletion voltage, much less improvement is observed in the charge collection efficiency.