Infrared Evaluation Techniques for Ge(Li) Detectors

The types of Ge(Li) detector spectrum degradation due to "trapping effects" are first considered, and a model is presented which explains this degradation in terms of specific phenomena. Then two detector evaluation techniques which utilize infrared light for studying these phenomena are outlined and the significant results obtained using these techniques are presented. The infrared absorption measurement yields information concerning apparent strain in the crystal which can be related to localized trapping effects in the detector. The detector response to monochromatic infrared light determines the presence of localized lithium precipitation (a major cause of spectrum tailing) and permits a quantitative measurement of the important carrier traps in germanium such as the lithium-defect trap, copper, nickel, and iron. Utilizing these measurements, it is possible to completely characterize the performance of a crystal and determine the source of detector degradation in one day. Very good correlation is consistently obtained.