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Dynamic Properties of Interstitial Carbon and Carbon-Carbon

P. Leary, R. Jones

Department of Physics, The University of Exeter, Exeter, EX4 4QL, UK

S. Öberg

Department of Mathematics, University of Luleå, Luleå, S95187, Sweden

V. J. Torres

Departamento de Física, Universidade de Aveiro, 3810 Aveiro, Portugal.

Physical Review B, 55, 2188, 1997


Interstitial carbon, C tex2html_wrap_inline334 , defects in Si exhibit a number of unexplained features. The C tex2html_wrap_inline334 defect in the neutral charge state of gives rise to two almost degenerate vibrational modes at 920 and 931 cm tex2html_wrap_inline338 whose 2:1 absorption intensity ratio naturally suggests a trigonal defect in conflict with uniaxial stress measurements. The di-carbon, C tex2html_wrap_inline340 -C tex2html_wrap_inline334 , defect is bi-stable, and the energy difference between its A and B forms is surprisingly small even though the bonding is very different. In the B-form appropriate to the neutral charge state, a silicon interstitial is believed to be located near a bond centered site between two C tex2html_wrap_inline340 atoms. This must give rise to vibrational modes which involve the motion of both C atoms in apparent conflict with the results of photoluminescence experiments. We use an ab initio LDF cluster method, AIMPRO, to calculate the structure and vibrational modes of these defects and find that the ratio of the absorption intensities of the local modes of C tex2html_wrap_inline334 is in reasonable agreement with experiment even though the structure of the defect is not trigonal. We also show that modes in the vicinity of those detected by PL for the B-form of the di-carbon center involve independent movements of the two C atoms. Finally, the trends in the relative energies of the A and B-forms in three charge states are investigated.

Antonio Resende
Wed Jan 15 12:41:08 GMT 1997