Study of charge transport in silicon detectors: Non-irradiated and irradiated

The electrical characteristics of silicon detectors (standard planar float zone and MESA detectors) as a function of the particle fluence can be extracted by the application of a model describing the transport of charge carriers generated in the detectors by ionizing particles. The current pulse response induced by alpha and beta particles in non-irradiated detectors and detectors irradiated up to fluences Phi approximate to 3.10(14) particles/cm(2) is reproduced via this model: i) by adding a small n-type region 15 pan deep on the p(+) side for the detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one additional dead layer of 14 mu m (observed experimentally) on each side of the detector, and introducing a second (delayed) component to the current pulse response. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about 5.10(13) particles/cm(2) and converging, beyond, to saturation values of about 1050 cm(2)/Vs and 450 cm(2)/Vs for electrons and holes, respectively. At a fluence Phi approximate to 10(14) particles/cm(2) (corresponding: to about ten years of operation at the CERN-LHC), charge collection deficits of about 14% for beta particles, 25% for alpha particles incident on the front and 35% for alpha particles incident on the back of the detector are found for both type of detectors.