Hydrogen in silicon: current understanding of diffusion and passivation mechanisms

A model for H diffusion and passivation is described that explains the experimental results from solar cell passivation, such as variations in the degree of passivation in substrates from different vendors, passivation due to forming gas anneals following Al alloying, and the effects of plasma enhanced chemical vapor deposition (PECVD) nitridation. Two major features of the model are inclusion of: (i) a new H diffusion mechanism involving hydrogen-vacancy complex {V-H} formation; and (ii) surface damage that causes high solubility of H at the Si surface and dissociation of molecular H at low temperatures. The theoretical analysis, based on static potential energy surfaces at the ab-initio Hartree-Fock level, identifies some details of diffusion mechanisms.