Hydrogen migration in doped and undoped polycrystalline and microcrystalline silicon

Hydrogen diffusion in phosphorous and boron doped polycrystalline and microcrystalline silicon was investigated by deuterium diffusion experiments. Deuterium concentration profiles were measured as a function of temperature, deuterium, and dopant concentrations. The effective diffusion coefficient is thermally activated and varies from 0.01 to 1.69 eV in response to changes in the deuterium and dopant concentrations. This variation is accompanied by a change of the diffusion prefactor by more than 15 orders of magnitude and is even consistent with results reported on H diffusion in hydrogenated amorphous silicon. Using the theoretical diffusion prefactor the energy EA required to yield the diffusion coefficient was calculated. EA reveals a Fermi energy dependence similar to that of the formation energy of H⁺ and H^- in c-Si. Based upon the experimental data a unified microscopic model for H diffusion is proposed.