| In this thesis work, two systems of semiconductor quantum dot nanostructures were investigated by an advanced technology which combines the chemically sensitive Z-contrast imaging and bonding sensitive electron energy-loss spectroscopy in scanning transmission electron microscope. The crystallographic structure, composition, and electronic properties of quantum dots were characterized at the atomic scale to understand structure-property relationship, which is important for the prospective device application of these quantum dot materials.; The results on the SnxSi1−x/Si multi-layer system revealed two types of formation mechanisms for Sn quantum dots. The first mechanism involved with a phase separation process of the SnxSi 1−x alloy layers, while the other one operated by filling the voids in the Si matrix with endotaxially grown Sn. Based on this void-mediated formation mechanism, a new method for growing quantum dots may be developed. The study of InAs quantum dots embedded in GaAs focused on the effects of a variety of growth parameters on the dots correlated with the optical properties of materials. The structural analysis provided key information for controlling the morphology of the quantum dots, and also preventing the degradation of the quality of materials. In particular, it was found that a newly developed pulsed laser annealing technique for post-growth annealing of materials can increase the number density of dots while keep the shape and size of dots unchanged. The diffusion mechanism behind this technique needs to be understood in the future study for further applications on other quantum dot materials. |
