The thermal diffusion of Ge implanted into SiO 2 films growth on a Si substrate has been studied by nuclear analyses and μ-Raman spectroscopy with and without the presence of co-implanted 30Si and 29Si barriers, each located from both sides of the Ge implanted distribution. Combination of Rutherford backscattering spectroscopy and Resonant nuclear reaction analysis shows that, under thermal activation at 1100°C, implanted Ge diffuses differently toward the sample surface and the SiO 2/Si interface due to the occurrence of Ge outgassing effects, as well as the non-homogenous distributions of the implanted ion species and the defects they have generated inside SiO 2. A maximum local atom concentration of co-implanted silicon as low as ∼1.6 at. % is found to completely block the germanium diffusion in both directions, leading to the formation of Ge nanocrystals and Si/Ge aggregates evidenced by μ-Raman spectroscopy. In addition to highlighting the role of Si excess on the Ge trapping mechanism, such a result makes the nominal silicon oxide stoichiometry and composition two crucial parameters to stabilize Ge during high temperature annealing, which explains the strong discrepancies reported for the Ge thermal diffusion coefficient in the literature.