A study of charge trapping in irradiated silicon with test beam data

This note describes an original method which has been developed to determine the trapping time constants in irradiated silicon using the data of the ATLAS Pixel Detector test beams. The charge collection efficiency is measured as a function of the drift length in irradiated silicon, and the charge carrier trapping lifetime is extracted comparing the data with a numerical simulation of the detector response to ionizing particles. The measurements have been performed on pixel detectors irradiated with protons to a fluence of $1.1 \cdot 10^{15}$~\nequ. A trapping lifetime of ($2.3 \pm 0.8$)~ns is found after annealing to minimum in full depletion voltage, while it is $(4.1 \pm 0.7)$~ns after 25~h annealing at 60~$^0$C. Comparison with measurements made with the transient current technique is discussed.