Anomalous B diffusion profiles in nanocrystalline Si

B concentration profiles measured by secondary ion mass spectrometry in a 250 nm thick nanocrystalline Si (nc-Si) layer made of 50 nm wide grains show unusual diffusion profiles. The usual B diffusion model, which takes into account the variation of the B lattice diffusion coefficient with B concentration, fails to explain the profiles measured in nc-Si. In contrast, B diffusion profiles can be well fitted using a model that takes into account moving grain boundaries with a B-concentration-dependent migration rate.