Charge Transport in Non-Irradiated and Irradiated Silicon Diodes

A model describing the transport of charge carriers generated in silicon detectors (standard planar float zone and MESA diodes) by ionizing particles is presented. The current pulse response induced by and particles in non-irradiated detectors and detectors irradiated up to fluences 3 10 particles/cm is reproduced through this model: i) by adding a small n-type region 15 m deep on the p side for the standard planar float zone detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one dead layer 14 m deep (observed experimentally) on each side, and introducing a second (delayed) component. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about 5 10 particles/cm and converging, beyond, to saturation values of about 1000 cm/Vs and 455 cm/Vs for electrons and holes, respectively. At a fluence 10 particles/cm, charge collection deficits of about 13% for particles, 25% for particles incident on the front and 35% for particles incident on the back of the detector are found for both type of diodes.