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The electrical properties and lattice disorders of 50 keV, focused ion beam (FIB) gallium-implanted silicon layers have been investigated as a function of beam scan speed and ion dose. The critical dose for continuous amorphous layer formation is 8 ∼ 10 × 1013 ions/cm2, when the beam scan speed is lowered to about 10−2 cm/s. This is about 1/3 that of conventional ion implantation. The increase in secondary defect formation after annealing is also observed as the beam scan speed decreases under implantation conditions close to the critical dose. However, the effect of high dose rate on the electrical activation of gallium atoms and critical dose reduction is not as significant as with FIB implantation by a lighter ion mass, such as boron. The results are compared with those obtained by conventional ion implantation.