An enhanced device simulation of heavily irradiated silicon detectors at cryogenic temperatures

Radiation hardness is a critical design concern for present and future silicon detectors in high energy physics. Tracking systems at the CERN Large Hadron Collider (LHC) are expected to operate for ten years and to receive fast hadron fluences equivalent to 10¹⁵ cm^-2 1MeV neutrons. Recently, low temperature operating conditions have been suggested as an effective means to mitigate the damaging effects of radiation on detector charge collection properties. In order to investigate this effect, simulations have been carried out using the ISE-TCAD DESSIS device simulator. The so-called "three-level" model has been used. A comprehensive analysis of the influence of the V₂, C_iO_i and V₂O defect capture cross-sections on the effective doping concentration (N_eff) as a function of temperature and fluence has been carried out. The capture cross sections have been varied in the range 10^-18-10^-12 cm². The simulated results are compared with charge collection spectra obtained with 1064 nm laser pulses on devices irradiated with 23 GeV protons as a function of detector bias voltage. To validate the model, a wide range of temperature and fluence has been studied using a 1-D simplified structure. Thousands of simulation results have been cross-checked with the experimental data. The data between 190 K (the lower limit for simulations due to computational difficulties) and 290 K are well reproduced for all of the fluences considered. We conclude that the three-level model can be successfully used to predict irradiated detector behavior down to a temperature of at least 190 K.