Excimer laser annealing is shown to be very promising to promote Sb incorporation in Ge up to concentrations as high as 1 × 1021 at./cm3. However, we demonstrate that when Ge is melted by laser irradiation, a high excess of vacancies is generated in the molten region. These vacancies induce Sb electrical deactivation at the melt depth through the formation of Sbm-Vn complexes that act as a sink for further Sb atoms, even leading Sb to back-diffuse towards the surface, against the concentration gradient. These results are fundamental for the realization of new generation Ge-based micro and optoelectronic devices.