The electrical activation and clustering of Ga implanted in crystalline Ge was investigated in the (0.3–1.2)×1021 Ga/cm3 concentration range. To this aim, Ge samples implanted with 50 keV gallium, and annealed at several temperatures up to 650 °C, have been subjected to a detailed structural and electrical characterization. The substrate was maintained at 77 K during implantation to avoid the formation of the honeycomb structure that occurs during implantation at room temperature of heavy ions at high fluence. Secondary ion mass spectrometry analyses indicated a negligible Ga diffusion and dopant loss during the thermal annealing. The carrier concentration in the recrystallized samples measured by Hall effect showed a maximum concentration of active Ga of ∼6.6×1020 Ga/cm3. A remarkable Ga deactivation occurred with increasing the annealing temperature from 450 to 650 °C although the sheet …