ICDS Conference, Sendai, Japan, 7.95

PECULIARITIES OF INTERSTITIAL CARBON AND DI-CARBON DEFECTS IN Si

R. Jones, P. Leary,

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

S. Öberg

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

V. TORRES

Departamento de Física, Universidade de Aveiro, 3800 Aveiro, Portugal.

Abstract

The C_i and C_s-C_i defects in Si exhibit several unexplained properties. In the neutral charge state, the C_i defect possesses two almost degenerate vibrational modes suggesting a trigonal defect in disagreement with the C_2v symmetry deduced from several experiments. The B-form of the second defect is believed to consist of a Si interstitial, Si_i, located near a BC site between two C_s atoms, in apparent conflict with the results of PL experiments which show that the C-related vibrational modes are decoupled. The structure and vibrational modes of both defects are analysed using LDF cluster theory. The degeneracy of the modes o f C_i is attributed to an almost D_3h structure, with a 3-fold axis along [01-1]. The modes of the di-carbon interstitial lead to a resolution of the long standing problem concerning the almost zero-shifts due to mixed isotopes in the 580 and 543 cm-1 local modes observed in PL studies.

Keywords: ab initio theory, carbon interstitials, silicon, vibrational modes