A 1/6 monolayer of GaAs was grown onto a very flat GaAs surface by using metal-organic vapor-phase epitaxial techniques, and 2-dimensional nuclei were studied by using high-vacuum scanning tunnelling microscopy. On the basis of the 2-dimensional nuclei densities, the surface diffusion coefficient at 530C was estimated to be equal to 2 x 10-6cm2/s. It was found that, during growth, the bunched-step (multi-step) separation saturated and was independent of the substrate misorientation angle. The results could be explained in terms of a mechanism that took account of 2-dimensional nucleus formation on the wider terraces, and their coalescence on ascending steps. A step-bunching simulation which was based upon this model revealed that the saturated multi-step separation was proportional to the 2-dimensional nucleus separation (that is, to the reciprocal of the square root of the density).

M.Kasu, N.Kobayashi: Journal of Applied Physics, 1995, 78[5], 3026-35