Radiation effects on surface and bulk properties of ATLAS18 silicon sensors under low- and high-dose γ irradiation and annealing

Silicon strip detectors for the ATLAS Inner Tracker (ITk) at the HL-LHC must withstand harsh radiation conditions, including fluences of up to 1.6 × 1 0 15 1 MeV n eq / cm 2 and total ionizing doses (TID) of up to 66 Mrad. These requirements are met using radiation-hard n + -in- p technology implemented in the ATLAS18 silicon strip sensors currently under production. This work presents a combined study of γ -irradiation effects in ATLAS18 silicon sensors, including both segmented miniature strip sensors (“minis”) and unsegmented MD8 diodes fabricated on ATLAS18 production wafers. The samples were irradiated with a 60 Co γ source to multiple low TIDs between 0.5 and 100 krad, corresponding to the dose range relevant for the early operational phase of the ITk tracker. Additional measurements extending up to a few Mrad were performed to investigate the saturation of surface related damage effects. Post-irradiation characterization included measurements of total, bulk, and surface leakage currents, as well as capacitance-voltage measurements used to extract the full depletion voltage. The thermal stability of radiation-induced defects was studied using isochronal annealing between 80 °C and 300 °C and isothermal annealing at 60 °C and 160 °C. In addition, complementary studies of MD8 diodes irradiated to ultra-high doses of several hundred Mrad, well beyond the ATLAS ITk requirements, are included to investigate possible bulk-related effects induced by pure γ irradiation and their annealing behavior. The combined analysis of low- and ultra-high-dose irradiation provides a comprehensive picture of surface- and bulk-related γ -induced effects in ATLAS18 silicon sensors and their thermal evolution.