Charge transport in non-irradiated and irradiated silicon diodes

Abstract

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 /spl alpha/ and /spl beta/ particles in non-irradiated detectors and detectors irradiated up to fluences /spl Phi//spl ap/3/spl middot/10/sup 14/ particles/cm/sup 2/ is reproduced through this model: i) by adding a small n-type region 15 /spl mu/m deep on the p/sup +/ 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 /spl mu/m 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/spl middot/10/sup 13/ particles/cm/sup 2/ and converging, beyond, to saturation values of about 1000 cm/sup 2//Vs and 455 cm/sup 2//Vs for electrons and holes, respectively. At a fluence /spl Phi//spl ap/10/sup 14/ particles/cm/sup 2/, charge collection deficits of about 13% for /spl beta/ particles, 25% for /spl alpha/ particles incident on the front and 35% for /spl alpha/ particles incident on the back of the detector are found for both type of diodes.