Lookup NU author(s): Professor Patrick Briddon
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Local vibrational modes of carbon impurities in relaxed Si1-xGex have been studied with infrared absorption spectroscopy in the composition range 0.05≤x≤0.50. Carbon modes with frequencies in the range 512-600 cm-1 are observed in 13C+-implanted Si1-xGex after annealing at 550°C. Measurements on samples coimplanted with 12C+ and 13C+ show that these modes originate from defects containing a single carbon atom and from the variation of the mode frequencies with composition x, the modes are assigned to substitutional carbon in Si1-xGex. Based on the frequencies obtained from a simple vibrational model, the observed modes are assigned to specific combinations of the four Si and Ge neighbors to the carbon. The intensities of the modes indicate that the combination of the four neighbors deviates from a random distribution. Ab initio local-density-functional cluster theory has been applied to calculate the structure and the local mode frequencies of substitutional carbon with n Ge and 4-n Si neighbors in a Si and a Ge cluster. The calculated frequencies are ∼9% higher than those observed, but the ordering and the splitting of the mode frequencies agree with our assignments.
Author(s): Hoffmann L, Bech Nielsen B, Nylandsted Larsen A, Leary P, Jones R, Briddon PR, Oberg S
Publication type: Article
Publication status: Published
Journal: Physical Review B - Condensed Matter and Materials Physics
Print publication date: 01/01/1999
ISSN (print): 0163-1829
ISSN (electronic): 1550-235X
Publisher: The American Physical Society
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