Ge Quantum Dot Self-Alignment on Vicinal Substrates

Abstract

In this chapter we propose a two-step growth process consisting of specific self-nanopatterning and subsequent self-assembly of Ge dots. During the first step, a nanostructured template layer is obtained by growth, which serves to order the Ge islands during the second step. Growth instabilities that develop during epitaxy of Si and Si_1−xGe_x on silicon substrates produce large-scale, highly corrugated, periodic and reproducible morphologies [1–8]. Such instabilities could be efficiently used as templates for subsequent ordering of Ge islands [9–13] without the need of sophisticated lithographic tools. To address this issue, perfect control and characterization of the morphological evolution of surface instabilities is needed. At the least, it is necessary to determine the optimized experimental conditions in order to develop specific patterns. Theoretical models used to describe stress-driven instability [14–21] present large discrepancies with experimental results. For instance, they neither explain the morphological evolution of the instability with the substrate orientation [7] nor the opposite effects of stresses of opposite sign are explained by the models. Also, morphological evolutions of the instabilities are still under debate, probably because kinetics (surface diffusion) [22, 23] and atomistic parameters (step edge energy), should also play a major role in these evolutions [24].

Moreover, the driving force of Ge island nucleation is not fully determined.