The growth of Ge on the (001) surfaces of Si was studied by means of scanning tunnelling microscopy. By monitoring the spatial distribution of two-dimensional Ge islands after sub-molecular deposition, anisotropies were found in the surface diffusivity and lateral sticking coefficient of Ge adatoms at various types of step. It was found that the fast direction for Ge surface diffusion was along the substrate dimer rows. The 2 types of monatomic step had very different lateral sticking coefficients for Ge adatoms. A metastable so-called hut cluster phase was found to provide a kinetic pathway for the transition between the 2-dimensional Ge layers and so-called macroscopic 3-dimensional clusters. The hut clusters had (105)-type facet planes, and nucleated preferentially at [100]-type steps. The nucleation barrier for the huts was lower than that for the macroscopic clusters, and therefore provided an easier path, for accommodating Ge adatoms from the gas phase, than did the direct formation of macroscopic clusters.

Y.W.Mo, M.G.Lagally: Journal of Crystal Growth, 1991, 111[1-4], 876-81