Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Physics

Supervisor

Lyudmila Goncharova

2nd Supervisor

Peter Simpson

Joint Supervisor

Abstract

In nanostructures (NSs), to acquire a fundamental understanding of the electronic states by studying the optical properties is inherently complicated. A widely used simplification to this problem comes about by developing a model for a small scale representation of types of NSs and applying it to a hierarchy of fabrication methods. However, this methodology fails to account for structural differences incurred by the fabrication method that lead to differences in the optical properties. Proper modelling is realized by first considering the proper range of experimental parameters individually as inputs to a theoretical model and applying the correct parameters to the corresponding fabrication method. This thesis studies the connection between the structural and optical properties of NSs as a function of the fabrication method, using, principally, x-ray photoemission, Rutherford backscattering, photoluminesence, and Raman spectroscopy.

Ion implanted Si and Ge quantum dots (QDs) in dielectric matrix were prepared to study the optical and structural properties, and compared against several other preparation methods. Ge QDs are known to exhibit a high concentration of defect states. The cause of these states was studied for QDs in a sapphire matrix and attributed to diffusion and desorption of Ge during annealing. Optical studies of Si QDs fabricated using an implantation mask revealed that state-filling and excitation transfer are important parameters in densely packed QD arrays. Structural analysis of Si QDs in silica revealed a well defined interface composed of Si$_2$O$_3$ and no stress was detected. Furthermore, the valence level was pinned at its bulk position possibly due to interface states. This information was used to refine our theoretical model of QDs and then compared with a range of crystalline and amorphous Si and Ge NSs. Stronger confinement effects were observed in amorphous Si and Ge NSs, possibly due to the nature of the interface or re-normalization of the effective mass as a function of NS size. These results establish a framework for proper parameter control in theoretical modelling.

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