Ge dots were grown on Si(001) substrates pre-covered with 0.05 to 0.1ML of carbon. The C pre-deposition reduces the dot size to less than 20nm at growth temperatures ranging from 450 to 550C. In situ scanning tunnelling microscopy showed that sub-monolayer C-deposition locally induced c(4 x 4) reconstruction. The reconstruction was assigned to clusters of six C atoms localized in the two topmost atomic layers in between two Si surface dimers. The non-uniform distribution of carbon together with the enhanced surface roughness give rise to the early onset of island formation at Ge coverages as low as 2.5ML. These islands show intense photoluminescence signals at 4K. scanning tunnelling microscopy and transmission electron microscopy showed that the islands were irregularly shaped. No faceting was detected up to coverages of 4ML. At 5.8ML of Ge islands with (105) side facets and a (001) top facet were observed.

Self-Organized Growth of Ge Quantum Dots on Si(001) Substrates Induced by Sub-Monolayer C Coverages. O.Leifeld, R.Hartmann, E.Müller, E.Kaxiras, K.Kern, D.Grützmacher: Nanotechnology, 1999, 10[2], 122-6