Alladi Ramakrishnan Hall

Continuum and Atomistic Modeling of quantum dot growth in heteroepitaxial systems

Madhav Ranganathan

IIT Kanpur

Heteroepitaxial semiconductor thin films, such as Germanium on Silicon, display spontaneous self-assembly into quantum dots. The root cause for quantum dot formation is the elastic strain due to the lattice mismatch between film (Germaniun) and the substrate (Silicon). This elastic strain increases with film thickness and eventually overcomes the surface energy and wetting interactions which try to keep the film flat. The exact mechanism of dot formation depends on the nature of the deposited film. When the deposited film consists of pure Germanium, quantum dots nucleate at random positions. On the other hand, when the deposited film is a Silicon-Germanium alloy, the quantum dots are formed due to an instability. We have modeled these regimes using atomistic kinetic Monte Carlo simulations and continuum linear elastic models and shown the nature of dot formation in both cases. The size distribution and alignment of dots is shown to depend on the growth parameters. Further, we have extended our methods to model growth on pre-patterned substrates where the quantum dots are uniform. The results are directly compared with molecular beam epitaxy experiments on these systems.