EFFECTS OF THE DEFECT STRUCTURE ON HYDROGEN TRANSPORT IN AMORPHOUS-SILICON

Hydrogen evolution transients were measured for hydrogenated amorphous silicon prepared by Si implantation of crystalline silicon and subseq uent hydrogen implantation. The evolution curves are found to be simil ar for different H concentrations but with entirely different atomic a nd nanoscale structures, as was evidenced by small-angle x-ray scatter ing and infrared absorption investigations [Phys. Rev. B 53, 4415 (199 6)]. This behavior is explained by a hydrogen-diffusion controlled eff usion with a limited density of sites in the amorphous material that c an be occupied by hydrogen. The experimental effusion curves are model ed by using diffusion coefficients in the implanted layers that were d etermined by secondary-ion mass spectrometry. Diffusion through a high ly disordered material of low H content is found to have an activation energy of 2.26 eV. (C) 1997 American Institute of Physics.