The formation of Ge islands during molecular beam epitaxial growth was a spontaneous process and these islands, i.e. dots, were usually randomly arranged. In order to implement these nanoscaled islands into device applications, ordering of epitaxial dots was a crucial step. A study was made of the molecular beam epitaxial growth of Ge islands on Si(001) substrates, containing <110>-oriented square and long stripe type patterns defined by anisotropic wet etching of Si, in order to provide more understanding of how surface diffusion of Ge atoms would influence the formation of Ge islands on various types of surfaces. It was found that there were preferential nucleation sites for Ge islands along the bottom edges of the Si ridges. The Ge islands at the edge positions were larger than those formed on the free surface and they could be regularly spaced. Due to the consumption of Ge at the bottom edges of ridge patterns, the density of Ge dots on the free surface varied between about 3 x 108 and about 109/cm2 when changing the spatial separation between two adjacent Si ridges (2 to 100μm). A Ge mean diffusion length of about 7.5μm was determined for Ge growth at 700C.

Surface Diffusion Limited Nucleation of Ge Dots on the Si(001) Surface. Y.H.Wu, C.Y.Wang, A.Elfving, G.V.Hansson, W.X.Ni: Materials Science and Engineering B, 2002, 89[1-3], 151-6