Abstraction of hydrogen by SiH radicals from hydrogenated amorphous silicon surfaces

The dynamics and energetics are presented of two Eley-Rideal reactions by which SiH radicals impinging at thermal energies on growth surfaces during plasma deposition of hydrogenated amorphous silicon (a-Si:H) films abstract hydrogen atoms from the surface and return to the gas phase as SiH₂ radicals. The reactions were observed during classical molecular-dynamics simulations of a-Si:H film deposition from SiH radicals impinging on an initially H-terminated Si(001)-(2 × 1) surface maintained at 500 K. The H-abstraction reaction may either produce a danging bond on the surface or eliminate a surface coordination defect. The computed activation energy barriers for the two hydrogen abstraction reactions are 0.15 and 0.07 eV, respectively, and the corresponding exothermic reaction energies are 0.20 and 0.30 eV. The effects of both reactions on the growth surface are examined through detailed analysis involving the local structural configurations and the associated bond angle and bond length distributions in the vicinity of the surface hydrogen abstraction sites.