The foreseen upgrade of the LHC to its high luminosity phase (HL-LHC), willmaximize the physics potential of the facility. The upgrade is expected toincrease the instantaneous luminosity by a factor of 5 and deliver anintegrated luminosity of 3000 fb-1 after 10 years of operation. As a result ofthe corresponding increase in radiation and pileup, the electromagneticcalorimetry in the CMS endcaps will sustain maximum integrated doses of 1.5 MGyand neutron fluences above 1e16 neq/cm2, necessitating their replacement forHL-LHC operation. The CMS collaboration has decided to replace the existing endcapelectromagnetic and hadronic calorimeters by a High Granularity Calorimeter(HGCAL) that will provide unprecedented information on electromagnetic andhadronic showers in the very high pileup of the HL-LHC. In order to employ Sidetectors in HGCAL and to address the challenges brought by the intenseradiation environment, an extensive R&D program has been initiated, comprisingproduction of prototype sensors of various types, sizes and thicknesses, theirqualification before and after irradiation to the expected levels, andaccompanying simulation studies. The ongoing investigation presented here includes measurements ofcurrent-voltage and capacitance-voltage characteristics, along with predictedcharge collection efficiences of the sensors irradiated to levels expected forthe HGCAL at HL-LHC. The status of the study and the first results of theperformance of neutron irradiated Si detectors, as well as their comparisonwith numerical simulations, are presented.
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