Temperature dependence of the long-term annealing behavior of neutron irradiated diodes from 8-inch p-type silicon wafers

Diehl L. Kałuzińska O.A. Mühlnikel M.C. Andersson M. Gerassyova N. Amer J. Sicking E. Groner D. Kieseler J. Defranchis M.
1 March 2026 Institute of Physics

Journal of Instrumentation
2026 #21 Issue 3

To face the higher levels of radiation due to the 10-fold increase in integrated luminosity during the High-Luminosity LHC, the CMS detector will replace the current Calorimeter Endcap (CE) using the High-Granularity Calorimeter (HGCAL) concept. The high-radiation regions of the CE, where fluences between 1.0·10¹⁴n_eq/cm²and 1.0·10¹⁶n_eq/cm²and doses of up to 2 MGy are expected considering an integrated luminosity of 3 ab^-1, will be equipped with silicon pad sensors. This includes the entire electromagnetic as well as parts of the hadronic section of the CE. The silicon sensors are processed on 8-inch p-type wafers with an active thickness of 300 μm, 200 μm and 120 µm and cut into hexagonal shapes for optimal use of the full wafer area and tiling. With each main sensor, several small test structures (e.g. pad diodes) are hosted on the wafers, used for quality assurance and radiation hardness tests. In order to investigate the radiation-induced bulk damage, these diodes have been irradiated with reactor neutrons at JSI (Jožef Stefan Institute, Ljubljana, Slovenia) to fluences between 5·10¹⁴n_eq/cm²2 and 1.5·10¹⁶n_eq/cm². This study focuses on the isothermal annealing behavior of the bulk material at different temperatures between 5.5°C and 60°C using electrical characterization and charge collection measurements. The results are used to extract the annealing time constants for this material and fluence range based on the Hamburg model approach to allow an estimation of the expected annealing effects in silicon sensors during the year-end technical stops and the long HL-LHC shutdowns. The annealing parameters found in this study will make it possible to model the annealing behavior of p-type silicon detector projects at HL-LHC fluence ranges better than the existing Hamburg model.

Radiation-hard detectors , Si microstrip and pad detectors

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Experimental Physics Department, CERN, Espl. des Particules 1, Geneva, Switzerland
Karlsruhe Institute of Technology, Engelbert-Arnold-Straße 4, Karlsruhe, Germany
Kirchhoff Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, Heidelberg, Germany
Uppsala University, Box 35, Uppsala, 751 03, Sweden
Al-Farabi Kazakh National University, Al-Farabi Avenue 71, Almaty, 050040, Kazakhstan
An Najah National University, Old Campus Street 7, Nablus, Palestine
HAN University of Applied Sciences, Ruitenberglaan 29, Arnhem, 6826 CC, Netherlands

Experimental Physics Department
Karlsruhe Institute of Technology
Kirchhoff Institute for Physics
Uppsala University
Al-Farabi Kazakh National University
An Najah National University
HAN University of Applied Sciences

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