School of Physics - Theses
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ItemA Study of Silicon on Diamond( 2021)In modern-day technology, silicon and silicon-based materials play a key role in the production of computing parts, specifically, the transistors within the chips. The exponential densification of transistors has caused the excess heat generated during operation to significantly hamper chip performance. This has led to the rise of hyperbolic language which refers to this problem as the `silicon apocalypse', and the material as `dark silicon', on account of each chip mostly being turned off to limit heating. The focus of this work lies in creating a silicon-based heterostructure with diamond, which has an unparalleled thermal conductivity, to effectively extract and dissipate heat directly from the chip. To realise such a structure, this work explored the usage of single crystal diamond as a substrate for silicon growth. As diamond had been previously grown on silicon carbide with limited coherence, shown in literature by other authors, the work begins by investigating the interface between 3C-SiC and a diamond substrate both experimentally and theoretically. It was found that 3C-SiC could form a coherent interface with diamond across several nanometres and that, through atomistic simulation, it was possible to realise greater regions of coherence. In the fabrication process, which involved heating thermally deposited silicon within an ultra high vacuum chamber, it was discovered that thin film dewetting became a major hurdle for long range coherence. This dewetting phenomenon and the behaviour of silicon on diamond during annealing then became the second major focus of this thesis to better understand how, or if, a coherent interface could be achieved between these two materials. To diminish the possibility of dewetting, which occurs with very thin films, PECVD silicon was chosen as an accessible method to time-efficiently deposit thicker layers. In spite of the benefits of PECVD silicon, crystallisation through annealing did not yield single crystal silicon. Instead, minimal interaction was found below 600C between the diamond substrate and silicon, which exhibited behaviour in line with PECVD silicon on other substrates as reported in the literature. However, at elevated temperatures around 1000C, a novel form of diamond etching was observed. The results gleaned from this work indicated that 3C-SiC/diamond heterostructures with a coherent interface could be produced, and thus, future applications are possible. The formation of a silicon and diamond heterostructure, however, was hampered by thin film dewetting and so further testing is needed to determine whether a coherent interface could be achieved using processing techniques applied in the case of 3C-SiC, but with thicker layers. By utilising a more accessible deposition method, namely PECVD, thicker layers became readily available on diamond substrate. Under thermal treatment, the PECVD silicon was found to crystallise into a polycrystalline layer, and at temperatures exceeding 1000C, even begin etching the diamond substrate. These series of studies bring to light several fundamental details of a silicon and diamond interface that are a prerequisite to the utilisation of diamond substrates in the future, especially with silicon-based materials.