Trapping Effects in Ge(Li) Detectors and Search for a Correlation with Characteristics Measured on the P-Type Crystals

Abstract

Various Ge(Li) detectors showing trapping effects (low energy tailing for an applied field of 103 V/cm) with uniform γ-ray irradiation have been studied using a collimated beam of 137Cs γ-rays. The following parameters have been determined : velocity, mobility, drift length and carrier lifetime. For many samples, a good agreement between experimental measurements of charge collection efficiency with the position of irradiation and calculated curves is obtained de monstrating that the trap distribution is uniform. The carrier velocities and mobilities are practically not modified in the samples showing trapping effects, but the drift lengths are lowered and, as a consequence, the carrier lifetimes. Various-measurements including infrared transmission spectra, etch-pit distributions, electron lifetimes have been made on the starting P-type crystals. Results are presented showing a valuable correlation between the electron lifetimes measured at 77°K by the pulse charge method and detector performance.