Study of charge Transport in Silicon Detectors: Non-Irradiated and Irradiated

Abstract

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 $\Phi \approx 3 \cdot 10^{14}$ particles/cm$^2$ is reproduced via this model: i) by adding a small n-type region 15 $\mu$m 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 $5 \cdot 10^{13}$ 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 $\Phi \approx 10^{14}$ 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