Charge Collection Physics in Semiconductor Detectors

Introduction The NASA-funded IUCF-LBL collaboration to study the effects of radiation damage and the subsequent annealing of high-purity germanium detectors continues. Radiation damage considerations are extremely important in long duration germanium detector applications in space and in many accelerator experiments. Damaging radiation, such as high-energy protons and neutrons, create giant disordered regions in the germanium crystal lattice that predominantly trap a few percent of the holes produced by ionizing radiation.' The resolution of the detector degrades, as the hole-trapping results in a low-energy tail on gamma-ray peaks. During the last few years the scope of the program has broadened to include a general study of the collection of charge, both electrons and holes, as they move through the germanium lattice in undamaged, as well as radiation-damaged detectors. Various tools such as escape peaks from high-energy gamma rays, as well as analytical and Monte Carlo gamma-ray line-shape calculations, help provide understanding of many interesting charge collection properties. In addition to the research on germanium detectors, the radiation-damage effects of 200-MeV protons on room temperature CdZnTe detectors have also been evaluated.