We have investigated the role of hydrogen in hydrogenated microcrystalline silicon (μc-Si:H) formation using hydrogen plasma treatments, in particular examining the possibility of subsurface reaction due to permeating hydrogen atoms, which leads to the crystallization of hydrogenated amorphous silicon (a-Si:H). It is demonstrated that the hydrogen plasma treatment of a-Si:H film on the anode using a cathode covered by a-Si:H film, which is inevitably coated during the deposition period, gives rise to the deposition of μc-Si:H over the a-Si:H layer, i.e., chemical transport takes place. It is also found that the pure hydrogen plasma treatment using a clean cathode induces only etching of the a-Si:H layer. These results imply that the present hydrogen plasma condition does not cause crystallization of a-Si:H but only etching, and that careful experimentation is required to determine the real subsurface reaction due to atomic hydrogen.
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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