6.7 CONCLUSIONS

This chapter reviewed recent progress in the development and investigation of lateral quantum nanostructures produced by organometallic chemical vapor deposition on nonplanar substrates. It was demonstrated that the formation of these nanostructures strongly relies on self-ordering effects. In particular, they directly relate to the self-limiting growth characteristics of a nonplanar surface, which result from the interplay of growth rate anisotropy, capillarity, and entropy of mixing effects. The combination of lithography for preparing the nonplanar substrate patterns prior to growth and the self-limiting surface evolution during growth yields lateral nanostructures with high regularity and reproducibility, and with very good interface quality. As compared with methods relying on spontaneous self-ordering, this seeded self-ordering technique is more demanding, in that it requires the preparation of the nonplanar surface template, which adds lithography and processing steps to the fabrication procedure. Moreover, the lateral density of the resulting nanostructures is determined by the lithography features, and thus the achievement of high lateral densities remains a challenge of the lithography step. However, using this approach one can obtain positional order of nanostructure arrays, which is far beyond what can be achieved today with spontaneous self-ordering approaches. In addition, the driving force towards the ordered phase in this approach is stronger than in currently used self-ordering schemes of semiconductor nanostructures. This results in nanostructure arrays with better uniformity over large substrate areas. The fact that vertical stacking of the lateral nanostructures on a nonplanar substrate can be done with vertical spacings approaching 10 nm helps...