Radiation hardness and precision timing study of silicon detectors for the CMS High Granularity Calorimeter (HGC)

The high luminosity upgraded LHC or Phase-II is expected to increase the instantaneous luminosity by a factor of 10 beyond the LHC's design value, expecting to deliver 250 fb⁻¹ per year for a further 10 years of operation. Under these conditions the performance degradation due to integrated radiation dose will need to be addressed. The CMS collaboration is planning to upgrade the forward calorimeters. The replacement is called the High Granularity Calorimeter (HGC) and it will be realized as a sampling calorimeter with layers of silicon detectors interleaved. The sensors will be realized as pad detectors with sizes of less that ∼1.0 cm² and an active thickness between 100 and 300 μm depending on the position, respectively, the expected radiation levels. For an integrated luminosity of 3000 fb⁻¹, the electromagnetic calorimetry will sustain integrated doses of 1.5 MGy (150 Mrads) and neutron fluences up to 10¹⁶ neq/cm². A radiation tolerance study after neutron irradiation of 300, 200, and 100 μm n-on-p and p-on-n silicon pads irradiated to fluences up to 1.6×10¹⁶ neq/cm² is presented. The properties of these diodes studied before and after irradiation were leakage current, capacitance, charge collection efficiency, annealing effects and timing capability. The results of these measurements validate these sensors as candidates for the HGC system.