Yukhymchuk V. Optical and morphological properties of low-dimensional structures based on of silicon, germanium, and their solid solutions

The thesis presents the solution of the problem of finding out the mechanisms and specific features of physical processes which determine the formation of germanium- and silicon-based nanostructures and the relationship of their morphological characteristics with structural and optical properties. The work generalizes the results of the studies of morphological, structural, and optical properties of self-assembled nanoislands formed by molecular beam epitaxy, at the variation of different technological parameters. An important role of interdiffusion in the process of self-assembled formation of GeSi nanoislands on Si substrates is shown. The interdiffusion results from non-uniform strain both in the nanoislands and in the surrounding areas. A considerable intermixing of the components within the islands affects the mechanical strain values as well as the islands size and determines the critical volume, at which the transition from pyramid-shape to dome-shape growth occurs. The properties of the nanostructures with GeSi islands are shown to be affected by the parameters of buffer layers used for the epitaxial deposition of Ge and by the processes of covering of the islands by the silicon layer because their shape, composition and relaxation degree depend on overgrowth temperature and cover layer thickness. A possibility of application of multilayer structures with GeSi islands as detectors of near infrared radiation is demonstrated. It is shown for planar SiGe layers, formed on Si substrates, doping with carbon provide controllable influence on the relaxation of strain in the structures. Radiative processes in Si-based nanostructures, fabricated by a transformation of a single-phase system SiOx into a two-phase one (Si+SiO2) at thermal annealing, are studied.