Premium
Vibrational Properties of the 〈001〉 Split Interstitial in Silicon
Author(s) -
Wruck D.
Publication year - 1978
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220890122
Subject(s) - dumbbell , silicon , degenerate energy levels , molecular vibration , interstitial defect , molecular physics , coupling constant , infrared , lattice (music) , atomic physics , chemistry , condensed matter physics , physics , doping , optics , quantum mechanics , raman spectroscopy , medicine , organic chemistry , acoustics , physical therapy
A theoretical investigation is made of the vibrational behaviour of the 〈001〉 split interstitial in silicon using the Green's function formalism. In particular, the cases of the Si‐Si, C–C, and C–Si dumbbell are discussed. For the numerical calculation of the vibrational frequencies a modified Keating force model is used, in which the coupling of the dumbbell stoms each with another and to the four nearest‐neighbour atoms as well as the changes in the force constants between these four neighbours are described in terms of the ratio d / x (2 d separation of the dumbbell atoms,4 a lattice constant). The calculations are performed with d / a as parameter using a perfect crystal Green's function determined from neutron scattering data. The results show for reasonable values of d / a (0.5 ≦ d / a ≦ 1) in the case of the equiatomic dumbbell (D 2d symmetry) the existence of two high‐frequency localized vibrations (an A 1 ‐ and a B 2 ‐ mode) and of two doubly degenerate (E ‐ type) resonance modes or localized modes near the maximum lattice frequency. In the case of the mixed dumbbell (C 2v symmetry) also two high‐frequency localized modes (both of A 1 ‐ type) and four resonance or low‐frequency localized modes (two of B 1 and two of B 2 ‐ type) are obtained. On the basis of the above calculations, an interpretation of the C(I) infrared absorption bands observed in carbon‐doped electron‐irradiated silicon crystals as the two A 1 ‐ modes of the C–Si〈001〉 dumbbell can be made on the basis of the absolute values of the frequencies and the relative line intensities but becomes difficult when considering also the separation of the two modes and its isotopic shift with respect to carbon.