The 1018 meV (W or I1) vibronic band in silicon

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Abstract
Uniaxial-stress and magnetic field perturbations confirm that the 'W' zero-phonon line, produced in crystalline silicon by radiation damage, occurs between spin-singlet, nondegenerate orbital states at a trigonal centre. The authors show that the excited state of the W line undergoes strong stress-induced interactions with both non-degenerate and doubly degenerate orbital states lying about 30 meV to higher energy. Although this is the major stress perturbation, there is negligible vibronic interaction of the excited states, and the vibronic properties of the W band are explained in terms of simple relaxation involving perturbed lattice modes. The one observed local vibrational mode of the centre has Si isotope effects consistent with its involving only Si atoms. The stress data are used to show that the series of W-like bands produced by bombarding Si with inert-gas ions may be W centres perturbed by the strain of a nearby inert-gas atom.