P-type ultrashallow junctions are widely fabricated using Ge preamorphization prior to ultralow-energy boron implantation. However, for future technology nodes, issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). An understanding of the effect of the buried Si/SiO2 interface on defect evolution, electrical activation, and diffusion is needed in order to optimize the preamorphization technique. In the present study, boron has been implanted in germanium preamorphized silicon and SOI wafers with different preamorphizing implant conditions. Subsequent to implantation an isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall-effect and secondary-ion-mass spectroscopy techniques. The results show a variety of interesting effects. For the case where the Ge preamorphization end-of-range defects are close to the buried oxide interface, there is less dopant deactivation and less transient-enhanced diffusion, due to a lower interstitial gradient towards the surface.