High Operating Temperature Limitations for Germanium Detectors

The operation of germanium spectrometers at temperatures considerably in excess of 77°K (with attendant advantages in the cooling system) has been made possible with the advent of high purity germanium. The basic limitations on operating temperature are due to (1) increased trapping effects and (2) increased electronic noise. An extensive analysis has been made of temperature-dependent noise sources. The principal limitation is due to trap and band-to-band bulk-generated currents. Experimentally determined parameters for germanium indicate that the operation of larger-volume detectors at temperatures in excess of 200°K is feasible. Several high purity detectors (1 cm3 and 14 cm3 in volume) have already been operated satisfactorily in the 170-180°K range, considerably higher than the 130-140°K maximum range observed for Ge(Li) detectors. In all detectors tested thus far, the principal limitation has been due to trap-generated current, which indicates the possibility of further improvement.