Characterization of Irradiated Silicon Sensors for HGCAL

As part of High Luminosity LHC (HL-LHC) project, the high-granularity calorimeter (HGCAL) will be a major upgrade of CMS experiment to replace the current endcap calorimeter. Due to the higher instantaneous luminosity of the HL-LHC and the rapidity range the HGCAL will cover, radiation tolerance is a primary design consideration. The majority of the HGCAL will be based on 120-, 200-, and 300 \textmu m thick silicon (Si) pad sensors and will sustain 1-MeV neutron equivalent fluences up to about 10\textasciicircum 16 neqcm\textasciicircum \textbraceleft -2\textbraceright . Campaigns have been underway to determine the level of degradation expected over the full life of the detector. A first study of irradiated test diode samples from 8-inch and 6-inch wafers at -30 \textdegree C is presented, including all three thicknesses and both bulk polarities. The electrical and charge collection properties are characterized after irradiation by current-voltage, capacitance-voltage and infrared Transient Current Technique measurements for sensors exposed to various fluence levels.