Diffusion of germanium in silica glass

The first measurements of the diffusion coefficient of substitutional germanium in silica glass are reported. Samples were prepared by implanting germanium ions into high purity silica. The concentration of germanium at the surface remained essentially zero, indicating that germanium evaporated readily from the surface of the sample. It was found that, during an initial anneal, the peak concentration of germanium shifted toward the surface. We attribute this to a drift motion of ions in the field created by the implant. The motion of the ions during an anneal could be changed by applying a DC electric field. A preliminary annealing procedure was established which eliminated the drift motion, so that the subsequent motion of germanium could be described as simple diffusion. EXAS measurements indicated that germanium was clustered together in the as-implanted samples, but that after this pre-anneal, germanium was incorporated into the matrix. The diffusion coefficient of the substitutional germanium in silica was found to be 7250 exp(−6.6 × 104/T) cm2/s, which corresponds to an activation energy, Q = 131 kcal/mol.