Radiation induced point- and cluster - related defects with strong impact to damage properties of silicon detectors

This work is focusing on the investigation of those radiation induced defects causing degradation effects of Silicon detector performance. Comparative studies of the defects induced by irradiation with Co⁶⁰- γ rays, 23 GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of some point defects and cluster related centers having a strong impact to damage properties of Si diodes. The detailed relation between the “microscopic” reasons as based on defect analysis and their “macroscopic” consequences for detector performance are presented. In particular, it is shown that the changes in the Si device properties (depletion voltage and leakage current) after exposing to high levels of Co⁶⁰- γ irradiation can be completely understood by the microscopically investigated formation of two point defects: i) a defect formed via a second order process (Ip) that can be associated with the long searched for V2O complex or with a Carbon related center and is the cause for the observed type inversion effect in Oxygen lean material; ii) a bistable donor (BD) created during irradiation that is strongly generated in Oxygen rich material, associated with one of the earlier thermal donors in Si. It is the cause for the observed positive space charge induced by irradiation in oxygenated Si diodes. Specific for hadron irradiation are the annealing effects which decrease resp. increase the originally observed damage effects as seen by the changes of the depletion voltage (effects known as “beneficial” and “reverse” annealing, respectively). A group of four cluster related defects proved to be responsible for these annealing effects. Their formation is not affected by the Oxygen content or Si growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions.