The dissertation is devoted to the investigation of the features of physical processes that cause thermally stimulated structural transformations in nanocomposites based on oxides of silicon, aluminum, hafnium and zirconium doped with one or more types of impurities (silicon, germanium, rare earth ions). The effect of these processes on the optical, electrical and luminescent characteristics of nanocomposites and structures based on them is clarified. It is shown that radio frequency magnetron sputtering allows the fabrication of thin composite layers and multilayer structures with the desirable characteristics.
The structure of the work reflects its evolution from the study of simpler materials, in particular, undoped or doped with one type of oxide impurity, to complex nanocomposites, when they are doped with several impurities and/or they are constructed as multilayer structures. This way - "from simple to complex" - allows not only to summarize the results of research, which were obtained gradually in the direction of complicating the types of materials and structures based on them, but also to trace the relationship between different materials in terms of evolution of their properties, common patterns and predict the properties of new, more complex, materials and identify ways and means of managing their parameters. The thesis contains seven sections that cover and summarize the results of research. The first section of the dissertation presents a review of the literature on the topic of the dissertation, describes the main methods of obtaining composite layers doped with silicon/germanium and rare earth ions. The second section describes methods of manufacturing composite layers and structures based on them. Different approaches in the production of samples by the method of radio frequency magnetron sputtering and atomic ball deposition are analyzed. It is shown that the change of different technological parameters (deposition temperature, partial gas pressure, target power) allows to control the chemical composition of composite layers, as well as to grow multilayer structures. Several experimental methods were used to get information on structural, optical, electric and luminescent properties of the samples. In particular, spectroscopic methods (study of photoluminescence and its excitation spectra, Raman scattering, infrared absorption, spectral ellipsometry) and structural methods (atomic force microscopy, X-ray diffraction, electron microscopy, atop probe tomography), and electrical methods are used. The main results of this work are the following.
It is established that the main mechanism of Si crystallites formation in oxide layers doped with silicon is spinodal decomposition and out-diffusion of oxygen. The mechanism of luminescence in such materials is elucidated and the key role of silicon crystallites in excitation of luminescence of rare earth ions is established. It is found that the quenching of rare earths photoluminescence in the (Si, Er)-SiO2 and (Si, Nd)-SiO2 layers annealed at high temperatures is due to the processes of segregation of rare earth ions and the formation of the corresponding silicates.
It is established the factors that allow the stabilization of amorphous structure of HfO2 and ZrO2. It is shown that upon thermal annealing of Si-HfO2 layers, which leads to the formation of Si crystallites, they are covered with SiOx shell, which separates them from HfO2 matrix.
The possibility of formation of Ge crystallites in HfO2 and ZrO2 due to spinodal decomposition which occurs at lower temperatures than in the case of Si-HfO2, is shown. This allows the creation of Ge crystallites embedded in the amorphous matrix of HfO2 or ZrO2. Memory effects are demonstrated in such materials.
A method of non-destructive express control of optical and structural properties of these materials by combining the methods of spectral ellipsometry and infrared spectroscopy is proposed.
The application of developed materials and structures for optical communication elements, solar cells, and flash nonvolatile memory is demonstrated.
