Metastable and equilibrium structures in semiconducting silicides.

The low temperature form of the iron disilicide (P-FeSi2) phase has been widely shown to be a promising material for Si-based opto-electronics devices due to its direct band gap (0.87 eV). These materials can be easily produced using a wide range of techniques. This work focuses on two techniques that utilises an ion beam, ion beam assisted deposition (IBAD) and ion beam synthesis (IBS). IBAD has been identified as a suitable technique for producing low cost material over large areas, which is particularly important for applications as solar cells, McKinty et al (2002), This thesis reports in details on the work to optimise the microstructures of four materials. Fe deposited on Si in the ratio of 29%; 71% and produced using IBAD and Fe implanted into- Si using IBS. Also the effect of implanting a transition metal is investigated, Fe implanted into an overlaid SiGe layer and Co implanted into FeSi2, both produced using IBS. Both the initial and annealed conditions were investigated using transmission election microscopy (TEM), x-ray diffraction (XRD) and Rutherford backscattering spectroscopy, (RBS) were used to characterise the microstructures. The results showed that in both techniques p-FeSi2 is formed in the initial condition. The effect of using a second beam during deposition was to increase nucleation on the Si substrate interface, resulting in a reduced grain size, as compared to non-IBAD samples. Samples deposited at 300°C or lower produced an amorphous beta-FeSi2 layer, while at temperatures higher than 300°C the formation of crystalline beta-FeSi2 phase were seen. Also the effect of the process parameters was investigated with respect to the microstructures produced. During thermal annealing the microstructures coarsened by Ostwald ripening. The second area of research was to study the phase equilibria in the Fe-Si binary and Co-Fe-Si ternary systems. The alloys were produced by the author using a plasma are furnace. Three annealing regimes were used in the study, 850°C for 24 hours, 900°C for 24 hours and 1000°C for 10 hours. Ten Co-Fe-Si alloys were produced with the compositions chosen specifically to reveal the phase equilibria of the ternary system. Electron microprobe analysis EPMA and XRD were used to characterise the system. Based on the results two isothermal surfaces, at 900°C and 1000°C, were proposed