SCANNING-TUNNELING-MICROSCOPY STUDY OF SURFACE-MORPHOLOGY AT THE INITIAL GROWTH STAGE OF SI ON A 7X7 SUPERLATTICE SURFACE OF SI(111)

Scanning-tunneling-microscopy (STM) images were taken from the surface of a Si layer grown at a rate of 0.6 nm/min on a Si(111)-7×7 substrate held at 250°C in order to study the surface morphology change in terms of the thin-film-growth process. Each STM image was obtained from the Si layer whose growth was terminated at an arbitrary value of the specular reflected high-energy electron-beam intensity (I). At the initial growth stage on the native Si(111)-7×7 substrate, the amplitude of I does not oscillate regularly, and three-dimensional (3D) islands nucleate and grow layer by layer. When a second bilayer has a mean thickness between 13/4 and 21/4 bilayers, the layer growth starts with the nucleation and growth of 2D islands, and is followed by regular oscillation in I. The transition from a 3D to a 2D growth mode can be deduced from the difference in the nucleation and growth processes of islands on the native Si(111)-7×7 substrate and the growing Si layer; this is because the latter surface is composed of small domains with metastable 2×1, 2×2, 5×5, 7×7, and 9×9 superlattices. © 1995 The American Physical Society.