Seminars and Journal Clubs
Development of ultra radiation hard silicon detectors for LHC Upgrade
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E.349
E.349
Description
Silicon particle detector have to survive operational in extremely harsh radiation environment after luminosity upgrade of the CERN LHC (Large Hadron Collider). The Super-LHC would result in an integrated fluence 1x10^16 p/cm2 and that is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies.
Particle radiation causes irreversible crystallographic defects in silicon material that deteriorate the detector performance. Electrically active defects are responsible for the changes in the operation of the particle detectors. First, the donor doping concentration of silicon is compensated by the acceptor type defects. This causes a space charge sign inversion (SCSI) in n-type silicon material and after the SCSI increase in detector full depletion voltage (Vfd). Second, leakage current of detector (Ileak) increases linearly as function of accumulated radiation fluence. The increases the shot noise of the detector and the heat dissipation of the tracker system. Third, overall charge collection efficiency (CCE) degrades because of trapping of charge carriers into the radiation induced defects. It is expected that the trapping will limit the charge collection depth to an effective range of 20 µm to 30 µm corresponding 80-90% dead volume of the detector. Thus, the trapping fundamentally limits the detector operation under Super-LHC conditions.
One concept of advanced radiation hard detectors is the use of charge or current injection. This is a development of CERN RD39 Collaboration and it is called current injected detector (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge. This leads to nearly uniform electric field through the detector at any operating voltage regardless of the radiation fluence. An important advantage of CID is that at some given operating voltage, the current decreases with increasing irradiation fluence. This would result in segmented detector decreasing shot noise with respect of increasing fluence. With CID concept it is additionally possible to increase the absolute value of the collected charge when the concentration of active trapping centers is reduced by cooling to low temperatures.