Surface and interface effects on the stability of SiGe nanoislands

Deposition of Ge upon Si substrates is the prototype of the mechanism called Stranski- Krastanov growth, i.e. the self-assembled formation of 3D islands, following the formation of a thin, 2D Wetting Layer. As is shown in Chapter 1, the nucleation of these islands is random and non-uniform when the deposition is performed upon the standard Si(001) substrate. Deposition of SiGe on different substrates of Si can lead, however, to a high degree of uniformity. Some examples are described in Chapters 3 and 4. The aim of this thesis is to supply a quantitative analysis for some peculiar phenomena concerning island nucleation that occurs on these non-standard substrates. This is performed through the evaluation of the internal energy of the island (including also effects on the substrate) as discussed at length in Chapter 2, where the elastic, surface and edge energy contributions are described, focusing particular attention to the second one, that turns out to be quite complicated. Particular attention is devoted to the island nucleation on stepped substrates of Si (Chapter 4). An in-depth analysis of the formation of faceting upon the substrate Si(1 1 10) is carried out in Chapter 5, whereas Chapter 6 deals with the transition from the faceting to three-dimensional islands on this peculiar system. Conclusions are drawn in Chapter 7. Appendices A and B contain some additional information regarding the elastic field and the description of surfaces. In Appendix C an analysis of the strained surface energy is carried out. In Appendix D some preliminary work performed during the PhD period on other impor- tant surfaces for the SiGe system is discussed. Finally at page 203 a Curriculum Vitae is reported.