Inter-defect charge exchange in silicon particle detectors at cryogenic temperatures

Silicon particle detectors in the next generation of experiments at the CERN Large Hadron Collider will be exposed to a very challenging radiation environment. The principal obstacle to long-term operation arises from changes in detector doping concentration (N_eff), which lead to an increase in required operating voltage. We have previously presented a model of inter-defect charge exchange between closely-spaced centres in the dense terminal clusters formed by hadron irradiation. This manifestly non-Shockley-Read-Hall mechanism leads to a marked increase in carrier generation rate and negative space charge over the SRH prediction. We present here measurements of spectra from ²⁴¹Am alpha particles and 1064 nm laser pulses as a function of bias over a range of temperatures. Values of N_eff and substrate type are extracted from the spectra and compared with the model. The model is implemented in both a commercial finite-element device simulator (ISE-TCAD) and a purpose-built simulation of inter-defect charge exchange. Deviations from the model are explored, and conclusions drawn as to the feasibility of operating silicon particle detectors at cryogenic temperatures.