The defect luminescence spectrum at 0.9351 eV in carbon-doped heat-treated or irradiated silicon

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Abstract
The electron-vibronic band with its no-phonon (NP) transition at 0.9351 eV which was recently detected in heat-treated silicon is strong after irradiation of silicon and has been studied in high-resolution photoluminescence. The defect exhibits a quasi-local mode of quantum energy h(cross) omega =66.3 meV which is observed as one- and two-phonon vibronic sidebands. The existence of an electronic excited state at an energy of 1.8 meV in excess of the upper level of the NP transition is demonstrated by temperature-controlled experiments. Uniaxial stress and Zeeman measurements show that the defect possesses rhombic I (C2v) point group symmetry, and that the NP line is a 'spin-1/2 to spin-1/2' ( Gamma 5 to Gamma 5) transition. The stress response is nonlinear due to the mixing of the two electronic states by the perturbation. Piezo-optical splitting and interaction parameters are determined. The g-values are gisotropic=2 for one level of the NP line and gx=3.65, gy=1.5 and gz=0.8 for the other level suggesting that the defect is a pseudo-donor with a tightly bound hole and a loosely localised electron. A carbon isotope effect is observed in the NP transition and in the local-mode satellite giving evidence that one carbon atom per optical centre is involved. Sample statistics and a boron-specific vibronic satellite (h(cross) omega =29.4 meV) suggest that boron is also involved.

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