A systematic study has been performed to reveal the role of atomic hydrogen in chemical annealing, where the deposition of a thin layer and treatment with atomic hydrogen are repeated alternately, for the fabrication of a stable structure. Structural relaxation resulting from impingement of atomic hydrogen on the growing surface is differentiated into two processes: the structural promoted relaxation on the surface and changes caused within the sub-surface depending on the conditions for deposition of the thin layer and the flux of atomic hydrogen. The structural changes within the sub-surface resulted in either the widening of the optical gap or crystallization at rather low substrate temperatures (T s: 100-150° C). High-quality a-Si:H with the optical gap of 1.87 eV exhibiting rather high stability against light soaking was successfully fabricated by this technique. The defect density of the film was 4×1015 cm-3 in its well annealed state and 6×1016 cm-3 in the saturated state. At high T s, on the other hand, the hydrogen treatment mainly enhanced chemical activities of the growing surface and resulted in either narrowing of the optical gap or promotion of the grain growth.

High quality wide gap hydrogenated amorphous silicon films were prepared using a hydrogen chemical annealing technique involving the deposition of thin amorphous silicon films followed by a hydrogen radical (and/or ion) treatment. Thick films were prepared by repeating this process many times. The substrate temperature and the hydrogen treatment time can be used to select optical band gaps ranging from 1.8 to 2.1 eV. Low dangling bond defect densities in the as-deposited films ranging from 3 to 8×1015 cm−3 were measured over the entire optical band gap range. The light induced dangling bond densities were less than those found in standard high quality amorphous silicon. The optical band gap is strongly correlated to the medium range structure characterized by the dihydride density. The electronic transport and stability are correlated with the Si–Si bonding environments and the associated short range order including bond angle and bond length distributions.

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