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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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Amorphous hydrogenated silicon-germanium alloys have been studied using a variety of junction-capacitance techniques to establish the dependence of the mobility gap electronic structure and the density of deep defects on the germanium content. The Urbach tail slope is observed to be nearly constant over the whole alloy range. The energy position of the dominant deep defect band near midgap is deduced and evidence for a shallower unoccupied defect band undergoing a large lattice relaxation is also observed. The total density of deep defects is found to increase exponentially with increasing germanium content and the details of this increase are shown to be consistent with a weak bond to dangling bond conversion model.