Hydrogen diffusion and mobile hydrogen in amorphous silicon

Diffusion phenomena in hydrogenated amorphous silicon (a-Si:H) are modeled assuming that mobile H excited from Si-H bonds normally annihilates at dangling-bond defects, as in the ``H collision'' model of light-induced metastability. This diffusion model explains the long-standing puzzle of the doping dependence of the hydrogen diffusion coefficient DH. It also yields the magnitudes of the DH Arrhenius prefactors in doped and undoped a-Si:H. Mobile H diffuses over an energy barrier of about 0.3 eV; at room temperature, its diffusion rate is slightly greater than that of H in crystalline Si.