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In this work, we studied the possibility of synthesizing nanocrystalline germanium (Ge) via dry and wet oxidation of both amorphous and polycrystalline Si₀.₅₄Ge₀.₄₆ films. In dry oxidation, Ge was rejected from the growing SiO₂ forming a Ge-rich polycrystalline layer. As for wet oxidation, Ge was incorporated into the oxide, forming a layer of mixed oxide, SixGe₁₋xOy. Formation of nanocrystalline Ge was observed when the layer of SixGe₁₋xOy was annealed in a N₂ ambient. We have fabricated a metal-insulator-semiconductor structure with nanocrystalline Ge embedded within the insulator layer to study its feasibility as a memory device. / Singapore-MIT Alliance (SMA)

Growth and evolution of germanium (Ge) nanocrystals embedded into a silicon oxide (SiO₂) system have been studied based on the Ge content of co-sputtered Ge-SiO₂ films using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. It was found that when the proportion of Ge relative to Ge oxide is 20%, TEM showed that annealing the samples at 800°C for 60 min resulted in the formation of a denuded region between the silicon/silicon oxide (Si/SiO₂) interface and a band of Ge nanocrystals towards the surface of the film. By introducing a 20nm thick thermal oxide barrier on top of the silicon (Si) substrate on which the film is deposited, no denuded region in the bulk of this sample is observed. It is proposed that this barrier is effective in reducing both Ge diffusion into the Si substrate and Si diffusion from the substrate into the film. Si diffusing from the Si substrate reduces the Ge oxide into Ge which can subsequently diffuse into the Si substrate. However, the oxide barrier is able to confine the Ge within the oxide matrix so that the denuded region in the bulk of the film cannot form. However the reduction in diffusion should be more significant for Ge as its diffusion coefficient is lower than Si due to its larger size. It is suggested that the denuded region consists of amorphous Ge diffusing towards the Si/SiO₂ interface. When the Ge content is increased to slightly more than 70%, TEM showed that Ge nanocrysyals formed after annealing at 800°C for only 30 min for samples with and without the oxide barrier. There is no denuded region between the Ge nanocrystals band and the Si/SiO₂ interface for both samples but it was observed that coarsening effects were more prominent in the film deposited on top of the oxide barrier. The reduction effect of Si on Ge oxide should not play a significant role in these samples as the Ge content is high. / Singapore-MIT Alliance (SMA)

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This thesis covers the application of the local density approximation of density functional theory to a variety of related processes in germanium and silicon. Effort has been made to use calculated results to explain experimentally observed phenomena. The behaviour of vacancies and vacancy clusters in germanium has been studied as these are the dominant intrinsic defects in the material. Particular attention was paid to the annealing mechanisms for the divacancy as a precursor to the growth of the larger clusters, for which the electrical properties and formation energies have been studied. Some preliminary work is also presented on the germanium self-interstitial structure and migration paths. Attention was then turned to a selection of dopant-vacancy defects in both silicon and germanium. An effort was made to explain recent experimental observations in silicon through investigating a number of defects related to the arsenic E-centre. Following this, the properties of donor-vacancy clusters in germanium were studied, and comparison with the results calculated for silicon suggest a significant parallel between the behaviour of the defects and dopants in the two materials. Finally, extensive work was performed on the diffusion of phosphorus and boron in germanium. Diffusion of both dopants was studied via interstitial and vacancy mediated paths as well as by a correlated exchange path not involving any intrinsic defects. The results obtained confirmed current theories of the mechanisms involved in the diffusion of the two defects, while also expanding the knowledge of other paths and giving Fermi level dependences for the energy and mechanism for diffusion of the two defects. Boron diffusion was found to exhibit strong Meyer-Neldel rule effects, which are used to explain the unusually high diffusivity prefactors and energy barriers calculated from experimental measurements for this dopant.

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Pui-kong Lim. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 73-75.