Steps and Ge epitaxy on vicinal Si (111) surfaces: an STM study

Using high-resolution scanning tunneling microscopy, we investigate the periodicity of mixed arrays of single and triple steps and the atomic structure of triple steps on three vicinal Si(111) samples with off-angles 1.5 ∘ ≤ θ ≤ 9.45 ∘ towards the [1¯1¯2] direction. The comparison between the (556) and (557) triple-step structure demonstrates that only the number of 7x7 terraces is affected by miscut. At variance with the singular Si(111) case, Ge epitaxy is strongly correlated to step morphology, resulting, at the critical coverage and small misorientation, in the nucleation of holed nanoislands from step-edge protrusions. During step-flow growth, stress-driven bunching of atomic steps (ripples) is observed on the (557) surface, indicating that this mechanism of stress relief of Si(001) vicinal surfaces works also on Si(111) surfaces.