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The main aim of this work was to measure the spectroscopic response of intentionally damaged MESA silicon detectors. A uniformly damaged region was created using protons delivered by the University of Montreal, Montreal, QC, Canada, 6-MV tandem accelerator at different energies and fluences. Only the back half of the detectors was damaged. The vacancy density created in the damaged region was built at a level of 7×1015 vacancies/cm3. The detectors were scanned over their whole volume with protons of well-defined ranges. The response characteristics were studied using protons backscattered from a thin gold foil at nine different primary proton beam energies. The highest energy was selected for allowing the protons to reach the ohmic side (n+-side). This reach confirms that the detectors thickness is 300 μm, accordingly to the wafer thickness. The scanning of the detectors from the undamaged frontside was performed with three different proton energies of ranges within the undamaged region. Two proton energies were selected for probing the transient region extending between the damaged and undamaged regions of the detectors. Three energies of protons were chosen to probe the damaged region of the diodes. The same set of energies was selected for the study of the detectors spectroscopic features while illuminating the detectors' backside. The measured spectroscopic responses of the irradiated detectors were compared to the response of the undamaged detector. For frontside illumination, the total charge collection efficiency (TCCE) was determined close to 100% and 50% for protons stopped in the undamaged and damaged region, respectively. In the case of backside illumination, the TCCE was significantly smaller for protons of low energy, about 15-30% at a depth of 100 μm, and increases up to 80%-85% for the highest proton energy stopped in the detector. The results show that the silicon detectors can be partly and strongly deteriorated by megaelectronvolt protons of fluences of 1011 p/cm2.
Date of Publication: Dec. 2004