Monitoring radiation damage in the ATLAS Pixel Detector

With the increasing radiation dose accumulated by the ATLAS Pixel Detector at the LHC, effects of radiation damage become more and more visible due to the creation of silicon crystal defects. The monitoring of the detector reveals an increase in the leakage current, which is proportional to the rising radiation dose. Measurements of the effective depletion voltage show a general trend of reduction due to the decrease of the effective n-doping concentration. The most recent measurement indicates that the depletion voltage is close to its expected minimum and thus that type-inversion is imminent in the innermost detector layer. A track-based method has been developed to estimate the depth of the depleted zone after type-inversion, allowing a continuous monitoring of the sensor performance. Results are, so far, in agreement with a complete depletion of the sensor.