The critical step distance of growths of Si on the Si(111)7 × 7 surface with and without a Sn layer which mediates the step flow is interpreted in terms of the Burton-Cabrera-Frank (BCF) theory and Walton's atomistic nucleation theory. A pseudo-parabolic approximation is used to derive the diffusion length of adatoms before re-evaporation, λs, the activation energy for the formation of the critical nucleus, Ei, and the size of the critical nuclei, i*. The surfactant epitaxy with the mediate is due to an increase in the activation energy for the island formation which results in a large critical step distance for the step flow. An approximate formula for the relation between deposition rate and critical step distance, or off-angle of the Si substrate, is proposed based on the analyses. © 1992.
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