Roles of atomic hydrogen in chemical annealing

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 4×10 15 cm -3 in its well annealed state and 6×10 16 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.