Hydrogen Concentration and Distribution in High-Purity Germanium Crystals

High-purity germanium crystals used for making nuclear radiation detectors are usually grown in a hydrogen ambient from a melt contained in a high-purity silica crucible. The benefits and problems encountered in using a hydrogen ambient are reviewed. A hydrogen concentration of about 2×1015cm-3 has been determined by growing crystals in hydrogen spiked with tritium and counting the tritium ß-decays in detectors made from these crystals. Annealing studies show that the hydrogen is strongly bound, either to defects or as H2 with a dissociation energy > 3eV. This is lowered to 1.8eV when copper is present. Etching defects in dislocation-free crystals grown in hydrogen have been found by etch stripping to have a density of about 1×107cm-3 and are estimated to contain 108H atoms each.