Investigation of the Anomaly in the Response of Silicon Semiconductor Radiation Detectors at Low Temperatures

Investigation of the response anomaly in silicon semiconductor radiation detectors cooled to temperatures below 40°K has been continued. Experiments with surface barrier detectors show that the mean temperature at which normally ionized impurity atoms accept electrons (as deduced from dE/dx measurement of the depletion depth) is a slowly varying function of the impurity concentration. This behavior is expected from the dependence of the Fermi level on the temperature, impurity concentration and ionization energy. Below the narrow temperature interval in which the majority of the impurity atoms accept electrons and hence become electrically neutral, particles which produce low ionization densities (beta particles) produce pulse heights with room temperature magnitudes, while particles with high ionization densities (alpha particles) produce pulse heights which are lower than those characteristic of room temperature operation and which depend on the detector bias voltage. The results of experiments conducted to investigate polarization effects in lithiumdrifted semiconductor radiation detectors are described.