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Investigation of the Symmetries of the Phonons in 4H and 6H-SiC by Infrared Absorption and Raman Spectroscopy
Linköping University, The Department of Physics, Chemistry and Biology.
2005 (English)Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
Abstract [en]

The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries.

The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2005. , 98 p.
Keyword [en]
Raman spectroscopy, Silicon Carbide (SiC), IR absorption Spectroscopy, Phonon displacements, Lattice dynamic model (LDM), 4h-SiC, 6H-SiC, Polar modes in SiC
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-6079ISRN: LiTH-IFM-EX-- 05/1524--SEOAI: oai:DiVA.org:liu-6079DiVA: diva2:21630
Presentation
2005-11-16, Rontgen, IFM, F huset, LIU, Linkoping, 13:15
Uppsok
teknik
Supervisors
Examiners
Available from: 2006-03-30 Created: 2006-03-30

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CiteExportLink to record
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Citation style
  • apa
  • harvard1
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