Charge transport in non-irradiated and irradiated silicon detectors

A model describing the transport of the carriers of the charge deposited in n-type silicon detectors by ionizing particles is presented. In order to reproduce the experimental current pulse responses induced by alpha and beta particles in non-irradiated and irradiated detectors up to fluences ($\Phi$) much beyond the n to p-type inversion, a n-type region 15 microns deep is introduced on the p$^+$ side of the diode. This model also gives mobilities decreasing linearily up to fluences of around $5 \cdot 10^{13}$ particles/cm$^2$, and beyond, converging to saturation values of about 1000 cm$^2$/Vs and 450 cm$^2$/Vs for electrons and holes, respectively. The charge carrier lifetime degradation, due to trapping with increased fluence, is responsible for a charge collection deficit for $\beta$ particles and for $\alpha$ particles found in agreement with direct CCE measurements.