We have studied by SIMS the diffusion of boron in Ge-preamorphised silicon over a range of anneal temperatures and times, focusing on the influence of the depth of the boron profile relative to the crystalline-amorphous (c/a) interface. It is shown that, for all durations, transient enhanced diffusion (TED) occurs on both sides of the c/a interface. For short annealing times, the amplitude of TED varies by about two orders of magnitude between the surface and the end-of-range (EOR) defect band, formed just below the original c/a interface. We propose a model in which TED arises from the coupling between a Si-interstitial supersaturated « box », the EOR defect region, whose supersaturation decreases with time as the EOR defects grow, and a surface whose recombination efficiency is close to that of a perfect sink. The model successfully describes the different behavior of deep and shallow boron profiles, without requiring the existence of a diffusion barrier.