Radiation hardness study of Silicon Detectors for the CMS High Granularity Calorimeter (HGCAL)

The high luminosity LHC (HL-LHC or Phase-II) is expected to increase the instantaneous luminosity of the LHC by a factor of about five, delivering similar to 250 fb(-1) per year between 2025 and 2035. Under these conditions the performance degradation of detectors due to integrated radiation dose/fluence will need to be addressed. The CMS collaboration is planning to upgrade many detector components, including the forward calorimeters. The replacement for the existing endcap preshower, electromagnetic and hadronic calorimeters is called the High Granularity Calorimeter (HGCAL) and it will be realized as a sampling calorimeter, including 40 layers of silicon detectors totalling 600m(2). The sensors will be realized as pad detectors with cell size between 0.5 and 1.0 cm(2) and an active thickness between 100 mu m and 300 mu m depending on their location in the endcaps. The thinner sensors will be used in the highest radiation environment. For an integrated luminosity of 3000 fb-(1), the electromagnetic calorimeter will have to sustain a maximum integrated dose of 1.5MGy and neutron fluences of 1 : 0 x 1016 neq/cm(2). A tolerance study after neutron irradiation of 300 mu m, 200 mu m, 100 mu m and 50 mu m n-on-p and p-on-n silicon pads irradiated to fluences up to 1 : 6 x 10(16) n(eq)/cm(2) is presented. The main properties of these diodes have been studied before and after irradiation: leakage current, capacitance, charge collection efficiency with laser and sensitivity to minimum ionizing particles with radioactive source (Sr-90). The results show a good performance even after the most extreme irradiation.