High Purity Germanium for Detector Fabrication

Abstract

The preparation of large (100) oriented germanium crystals with net concentrations of electrically active impurities in the range 1-10 × 1010cm-3 is described. This material has been used successfully for the fabrication of semiconductor detectors having depletion layers up to 8 mm thick, without using lithium compensation. Electrical evaluation is performed by studying the Hall coefficient as a function of temperature, and by measuring the resistivity along the length at 77°K. Dislocation densities in most crystals range from 2000 to 5000 cm-2 Several dislocation-free crystals have also been grown. The oxygen concentration, measured by lithium precipitation, is approximately 1014 cm-3 in germanium grown from quartz crucibles and much less than this when grown from graphite. The solubility of lithium in pure, oxygen-free germanium is found to be 3.5 × 1013cm-3 at 23°C.