Optical and structural properties of SiO{sub x} films grown by molecular beam deposition: Effect of the Si concentration and annealing temperature
- Department of Chemistry, University of Helsinki, P. O. Box 55, Helsinki FI-00014 (Finland)
- Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto (Finland)
- Department of Micro and Nanosciences, Aalto University, P.O. Box 13500, FI-02150, Aalto (Finland)
We study the properties of Si-rich silicon oxide SiO{sub x} (x < 2) films grown on silica substrates by molecular beam deposition, in a wide range of Si content and annealing temperatures. The measured refractive index and absorption coefficient are successfully described using the effective medium approximation and the chemical compositions measured by x-ray photoelectron spectroscopy (XPS). The Si-SiO{sub 2} phase separation and the degree of Si crystallization increase with the annealing temperature; however, even after annealing at 1200 Degree-Sign C, the samples contain a large proportion of suboxides and partially disordered Si. The Si Raman signal and the absorption coefficient are nearly proportional to the amount of elemental Si provided by XPS. On the other hand, the Si Raman signal is much weaker than it is expected from the amount of elemental Si, which can be explained by the presence of ultra-small Si nanocrystals (diameters < 2 nm) and/or by the difference in the properties of bulk and nanoscale Si. The 1.5-eV photoluminescence (PL) intensity is the highest for annealing at 1100-1150 Degree-Sign C and x = 1.8-1.9. In contrast, the PL quantum yield steadily increases when the intensity of the Si Raman signal decreases. This observation suggests that the Si nanocrystals observed in the Raman spectra are not direct light-emitting centers. The temperatures induced by laser light in these films are surprisingly high, especially at the highest Si content (x {approx} 1.3). The laser-induced temperature (up to {approx}350 Degree-Sign C) substantially down-shifts the Raman band of Si nanocrystals (in our experiments from {approx}518 to {approx}512 cm{sup -1}) and increases the absorption coefficient (by a factor of {approx}1.4).
- OSTI ID:
- 22089574
- Journal Information:
- Journal of Applied Physics, Vol. 112, Issue 9; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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