Modeling of electric field in silicon micro-strip detectors irradiated with neutrons and pions

Edge-TCT method was used to extract velocity profiles in heavily irradiated silicon micro-strip detectors. Detectors were irradiated up to $10^{16} \rm{cm}^{-2}$ with reactor neutrons, 200 MeV pions and a combination of both. A simple electric field model assuming two space charge regions at each side of the detector and neutral bulk in-between was found to describe the field profile. It was observed that after heavy irradiation a sizeable electric field is present in the entire detector volume. For pion-irradiated detectors strikingly different profiles were obtained and attributed to the large oxygen concentration in the detector bulk. The model parameters were also studied during the long term annealing. The space charge region near the strips was found to shrink which in turn leads to larger electric field and impact ionization. The model parameters extracted from the measurements were fed to the device simulation program which showed reasonable agreement between simulated and measured data at lower fluences.