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TitleRaman spectroscopy of nanocrystalline and amorphous GaN
Publication TypeJournal Article
Year of Publication2005
AuthorsTrodahl, H.J., Budde F., Ruck B.J., Granville S., Koo A., and Bittar A.
JournalJournal of Applied Physics
Date Published2005
ISSN00218979 (ISSN)
KeywordsAmorphous materials, Crystallites, Deposition, Gallium nitride, Growth kinetics, Ion energy, Molecular vibrations, Nanostructured materials, Natural frequencies, Oxygen, Phonon energy, Phonons, Raman scattering, Raman spectroscopy, Thin films, Translational symmetry, X ray diffraction analysis
AbstractWe report Raman measurements on thin films of strongly disordered GaN and GaN:O prepared by ion-assisted deposition. The incident photon energies used in the experiments ranged from 1.95 to 3.8 eV, spanning the interband edge. Under subgap excitation the signal resembles the crystalline GaN vibrational density-of-modes, with significant broadening as expected for disordered material. There is a strong resonant behavior at the interband edge of the same mode for which a strong resonance is found in crystalline GaN, with a width suggesting that the entire vibrational branch contributes to the signal. Even nanocrystalline material is found to display Raman spectra characteristic of very short-range (<1 n) translational symmetry, in agreement with x-ray diffraction evidence for the random stacking nature of the 3 nm diameter crystallites. The presence of oxygen at even 25 at.% has only a subtle effect on Raman spectra at the network vibrational frequencies below 800 cm-1, but its presence is signaled by the appearance of an oxygen mode at 1000 cm-1. An N2 line at 2360 cm-1 correlates with a nitrogen excess introduced during growth. © 2005 American Institute of Physics.

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