Germanium spectrometers with internal junctions

For fabricating a spectrometer from a high purity Ge crystal with an internal junction two contact configurations are possible: pvπn or pπvn, where n and π represent the high purity n and p portions respectively. The two configurations are compared theoretically and experimentally with respect to depletion voltages, pulse risetimes, charge collection efficiencies and γ-ray pulse height resolutions. It is shown that the pvπn configuration has advantages in depletion voltage, charge collection, and timing properties as a result of the more favorable electric field. Spectrometers with depletion depths of 3 cm at 2000 V have been made from material having a net concentration gradient of dopants of 5 x 10 -9cm-4. The charge trapping in the Ge limited the high energy (approximately 1 MeV) γ-ray resolutions to about 0.4% for a 3 cm pvπn device. For spectroscopy of high energy charged particles, however, these diodes combine a thin entrance window (<50μg/cm2)with a large stopping power and should be very useful. (Auth.)