In situ TEM study of the growth of Ge on Si(111)

We have used the UHV-TEM to study the growth of Ge on Si(111) in situ, from the deposition of the fuse monolayer to complete relaxation by the introduction of dislocations. We show that, at 650 degrees C, the growth of Ge islands is dominated by seeps on the surface. Indeed, islands nucleated on steps that run along the (11 (2) over bar) direction have a very high aspect ratio, while other islands are roughly triangular in shape. Dislocations form initially exclusively by coalescence of these smaller islands. Further growth involves a complicated competition between surrounding strained islands and the relaxed island. At lower temperature (350 degrees C), steps still are a preferred site for island formation, but the limited surface diffusion makes it possible for islands to also nucleate on flat terraces. In this case, an island grows by incorporating dislocations at its edge, which results in a completely relaxed island from the start, and a very uniform network of dislocations. These in situ electron microscopy studies reveal a much more complicated and rich growth process than previously imagined, and tie previously obtained results together into a single picture.