Study of radiation damage in silicon detectors for high ... - F9

8 1. IntroductionForward SCTBarrel SCTPixel DetectorsTRTFigure 1.3: Schematic layout of the ATLAS Inner Detector (ID).This work presents results obtained by the study of radiation induced defects ofsilicon bulk under controlled conditions. Biasing voltage and temperature were controlledduring and after irradiations. Irradiation ux was varied from about 10 8 to few times10 15 n/cm 2 s to search for a ux eect on defect creation. Frequent measurements ofreverse current and full depletion voltage were performed during and immediately after theirradiation to provide better insight into fast defect annealing. Finally, abias dependentdefect annealing was discovered, resulting in about two times higher full depletion voltageof the biased samples after the end of benecial annealing.Radiation damage caused in silicon detectors can be separated to damage to siliconbulk and surface damage. The latter is mainly due to xed positive charges, collected atthe border between the semiconductor and the oxide. It increases the conductivity of thesurface, giving rise to surface currents. Surface damage can also distort the eld belowthe surface structures, thus changing the operation properties of a detector. It dependsconsiderably on detector design and manufacturing, which have been well studied andunderstood. Thus the surface damage seems to be manageable. Bulk damage, on theother hand, is much less understood. It causes an increase of the leakage current and ofthe eective dopant concentration. This results in increased operation voltage, increasednoise due to leakage current and increased power consumption and therefore heat. Allthose eects signicantly inuence the operational capability ofa silicon detector.Due to the interaction of radiation (n, p, , e, etc.)with silicon atoms the