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Substitutional carbon in Si1-xGex

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.

Publication metadata

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

Year: 1999

Volume: 60

Issue: 19

Pages: 13573-13581

Print publication date: 01/01/1999

ISSN (print): 0163-1829

ISSN (electronic): 1550-235X

Publisher: The American Physical Society


DOI: 10.1103/PhysRevB.60.13573


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