Optical properties of beta-iron silicide, ruthenium silicide and osmium silicide: Semiconducting transition metal silicides

Various optical techniques were used to study the semiconducting transition metal silicides of β-FeSi₂, Ru₂Si₃, and OsSi₂. The Raman spectra of ion beam synthesized (IBS) β-FeSi ₂ were shown to provide evidence of a net tensile stress in these IBS materials. Possible origins of the observed stress were suggested and a simple model was proposed in order to calculate a value of the observed stress. A correlation between the tensile stress, the nature of the band gap, and the resulting light emitting properties of IBS β-FeSi₂ was suggested. The photoreflectance (PR) spectra of IBS β-FeSi₂ reveals a direct gap at 0.815 eV and were shown to agree with the band gap value obtained by photoluminescence (PL) once the adjustments for the temperature difference and trap related recombination effects were made. This provides very convincing evidence for intrinsic light emission from IBS β-FeSi₂. Furthermore, a model was developed that helps to clarify the variety of inconsistent results obtained by optical absorption measurements. When the results of PL and PR were inserted into this model, a good agreement was obtained with our measured optical absorption results. We also obtained PR spectra of β-FeSi ₂ thin films grown by molecular beam epitaxy. These spectra reveal the multiple direct transitions near the fundamental absorption edge of β-FeSi ₂ that were predicted by theory. We suggest an order of these critical point transitions following the trends reported in the theoretical investigations. Doping these β-FeSi₂ thin films with small amounts of chromium was shown to have a measurable effect on the interband optical spectra. We also report on the effects of alloying β-FeSi₂ with cobalt. A decrease in the critical point transitions nearest the fundamental absorption edge was observed as the cobalt concentration increased. Finally, Raman spectroscopy was used to study the vibrational properties of β-FeSi₂. The measured Raman spectra agreed very well with the results predicted by group theory.; The optical properties of Ru₂Si₃ single crystals and polycrystalline thin films were explored using spectroscopic ellipsometry, ultraviolet to the near infrared (UV-VIS-NIR) transmission and reflectivity measurements, photothermal deflection spectroscopy, and Raman spectroscopy. We determined that the fundamental transition is direct with a value of 0.85 ± 0.01 eV. The dielectric function was measured over a large energy range using spectroscopic ellipsometry and compared to theoretical results. A very good agreement was obtained between experiment and theory. Raman spectroscopy was used to study the vibrational properties of both the Ru₂Si₃ single crystals and polycrystalline thin films.; The optical properties of bulk polycrystalline OsSi₂ were explored using spectroscopic ellipsometry, UV-VIS-NIR reflectivity measurements, and Raman spectroscopy. We determined the first direct transition to have a value of about 1.88 eV. The dielectric function was measured over a large energy range using spectroscopic ellipsometry and compared to theoretical results. A very good agreement was obtained between experiment and theory. Raman spectroscopy was used to study the vibrational properties of OsSi ₂. An electroless metal deposition technique was used to deposit thin films of osmium onto a silicon substrate and a brief summary of the results were given. We suggest that this method of depositing osmium is safer and more economical than conventional techniques such as e-beam evaporation.