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 α and β particles in non-irradiated detectors and detectors irradiated up to fluences Φ≈3·10¹⁴ particles/cm ² is reproduced through this model: i) by adding a small n-type region 15 μm 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 μm deep (observed experimentally) on each side, and introducing a second (delayed) component. For both types of detectors, the model gives mobilities decreasing linearity up to fluences of about 5·10¹³ particles/cm² and converging, beyond, to saturation values of about 1000 cm²/Vs and 455 cm ²/Vs for electrons and holes, respectively. At a fluence Φ≈10¹⁴ particles/cm², charge collection deficits of about 13% for β particles, 25% for α particles incident on the front and 35% for α particles incident on the back of the detector are found for both type of diodes