Direct observation and measurements of neutron-induced deep levels responsible for Neff changes in high-resistivity silicon detectors using TCT

Neutron-irradiation-induced deep levels responsible for changes of the space charge concentration Neff in high-resistivity silicon detectors have been revealed directly using the Transient Current Technique (TCT). It has been observed by TCT that the absolute value and sign of Neff experience changes due to the trapping of non-equilibrium free carriers generated near the surface (about 5 μm depth into the silicon) by short wavelength laser pulses in fully depleted detectors. Electron trapping causes Neff to change towards negative direction (or more acceptor-like space charges) and hole trapping causes Neff to change towards positive direction (or more donor-like space charges). The specific temperatures associated with these Neff changes are the freeze-out temperatures for free carrier emission from the corresponding deep levels. The carrier capture cross sections of various deep levels have been measured directly using TCT with different free carrier injection schemes.