SURFACTANT EPITAXY OF SI ON SI(111) SURFACE MEDIATED BY A SN LAYER .2. CRITICAL STEP FLOW OF THE GROWTH WITH AND WITHOUT MEDIATE

The critical step distance of growths of Si on the Si(111)7 x 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, lambda(s), the activation energy for the formation of the critical nucleus, E(i), 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.