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We simulated hydrogenated nanocrystalline silicon with molecular dynamics calculations using embedding and melt-quenching approaches. The embedding approach generates a well-defined crystallite residing in an amorphous matrix and a structure free of coordination defects. The H-distribution is inhomogeneous with an excess hydrogen density at the strained grain boundary between the nanocrystallite and the amorphous matrix. The amorphous matrix is better ordered in hydrogenated nanocrystalline-Si than in the homogenous amorphous silicon networks. Nanocrystals have been annealed at higher temperature where the nanocrystalline regions shrink in size. Nucleation and growth theory of these nanocrystals is developed. Melt-quenching simulations generate nc-Si structures which do not show a disordered grain boundary but generate a very high density of defects in the amorphous region, which cannot be annealed. The embedding approach may favor structures closer to experimental H-diluted growth conditions. Melt-quenching may better represent structures formed by laser induced recrystallization. [ABSTRACT FROM AUTHOR]

We examine different types of order measured in hydrogenated amorphous silicon (a-Si:H) and their effect on the optical absorption (band gap). We first review previous experimental work determining order on a short-range scale as probed by Raman spectroscopy, and provide, using molecular dynamics simulations, a theoretical explanation for why the band gap increases when this type of ordering is improved. We then present results on a-Si:H films deposited by hot wire chemical vapor deposition (CVD) and plasma enhanced CVD where the short-range order, from Raman spectroscopy, does not change, but order on a larger or medium-range scale does. This order is determined by measuring the width of the first x-ray diffraction peak, and was varied by depositing films at different substrate temperatures and/or different hydrogen dilutions. We find that the film band gap also increases when this type of ordering improves, and we provide a possible mechanism to explain these trends. We also suggest that much of the previous literature showing an increase in band gap with increasing film hydrogen content should be treated with caution, as these works may not have accurately deconvoluted the effects of optical adsorption due to film hydrogenation from those due to both types of lattice ordering. Finally, we argue that this same trend may apply, to a limited extent, to microcrystalline silicon. [ABSTRACT FROM AUTHOR]

Investigates the role of the atomic hydrogen by molecular dynamics simulations of the hydrogen deposition process. Analysis on backscattering events in a-Si:H and C-Si; Displacements of the silicon and hydrogen atoms of the substrate from their initial positions; Techniques used for growing a-Si:H films.