Restoration of lithium driftability in some vacuum-grown germanium crystals for gamma-ray detectors

Abstract

Germanium crystals used for γ-ray detectors frequently exhibit slow or non-uniform lithium-ion drift. The presence of oxygen is one known cause. However, it has been found in these laboratories that in large (~ 1kg) germanium crystals grown by the Czochralski method under vacuum, the presence of a fast diffusing impurity (probably copper) also leads to variable drift. Normal, uniform drift in these crystals has been restored by using gallium-indium alloys as a getter at ~ 800°C. The method is described in detail and the effects on crystal resistivity, dislocation density and lithium drift rate are presented. Gamma-ray detectors fabricated from gettered material show high resolution characteristics.