Relation between Microscopic Defects and Macroscopic Changes in Silicon Detector Properties after Hadron Irradiation

Silicon detectors produced from materials with different doping and oxygen concentration have been irradiated with 27 MeV and 23 GeV protons, 192 MeV pions and 5.3 MeV neutrons. In isothermal annealing studies at 60°C the microscopic defect evolution (measured with DLTS) and the changes in the detector leakage current were monitored in parallel. It is shown that the annealing of a broad DLTS peak located at about 0.42eV below the conduction band is correlated with a decrease of leakage current. This electron trap is at least partly attributed to the singly charged divacancy. At the same time an electron trap level at about EC-0.24eV which is commonly attributed to the doubly charged divacancy level is growing with increasing annealing time. The annealing process of both electron traps (EC-0.42 and EC-0.24 eV) and the annealing of the current related damage parameter α have been found to be independent of the oxygen and doping concentration in the materials under investigation (2×10 < [O] < 10cm and 10 < [P] < 4×10cm). Furthermore the introduction rate of the defect level at EC-0.42 eV and the current related damage parameter α are independent of the type of used particle, if the particle fluence is normalized to the non ionizing energy loss (NIEL). However, the introduction rates of the observed point defects VO and CiCs were found to depend on the particle type. Thus clear indication is given that the generation of point defects does not scale with the NIEL. Compared to the neutron irradiated samples the introduction rate of point defects after irradiation with charged hadrons was found to be higher by a factor between 1.6 and 2.2.