The impact of neutral base region on the collected charge in heavily irradiated silicon detectors

The collected charge in Si detectors irradiated up to the fluences of Super-LHC range (1016 neq cm−2) is calculated using an approach of double peak electric field distribution with an active base region. In the calculations the base region located between the space charge regions is considered as an active element of the detector structure in which the electric field is non-zero and depends on the irradiation fluence. With this advanced approach, the collected charge vs. fluence dependences is calculated and compared to those obtained using a standard linear electric field in an irradiated Si detector. The study is carried out for pad detectors, and for strip detectors with a strip pitch of 80 μm typical for ATLAS topology. It is shown that at the fluence ≥1015 cm−2 the electric field in the active base stimulates an increase of the collected charge by a factor of 1.3 and 4.2 in strip and pad detectors, respectively. The values of the collected charge calculated in the assumption of the double peak electric field and active base are still smaller than the experimental data. This suggests that additional effects may contribute to the collected charge that is under study.