C s–H 2* defect in crystalline silicon

Abstract

An infrared absorption study has been carried out on hydrogen-doped Si crystals with high carbon content. Hydrogen (deuterium) was introduced into the crystals by high-temperature (1250–1350°C) in-diffusion from H 2 (D 2) gas ambient. After hydrogenation several local vibrational mode lines were observed in the ranges of 660–690, 790–820, 1920–1960, 2120–2230, and 2680–2950 cm −1. Two Si–H (Si–D) lines with frequencies at 792.0 (571.6) and 1921.8 (1401.2) cm −1 were found to have the same dependence on hydrogenation temperature and the same annealing behaviour, therefore they were assigned to a single defect. Measurements on samples co-doped with hydrogen and deuterium revealed the appearance of new lines at 793.2, 1400.3, and 1922.7 cm −1 indicating that the defect of interest incorporates two weakly interacting hydrogen atoms. Uniaxial stress measurements showed that the 792.0 cm −1 line represents an E mode (two-fold degenerate) of a trigonal centre. A correlation was found in annealing behaviour of the lines at 792.0 and 1921.8 cm −1 with that of a line at 2752.3 cm −1. The lines at 792.0 and 1921.8 cm −1 were assigned to Si–H bend and stretch modes, respectively, and the line at 2752.3 cm −1 to a C–H stretch mode of a CH 2* complex with C 3v symmetry. One hydrogen atom of the complex is bound to a C atom and locates on C 3v axis close to bond-centre site, and the other is bound to a Si atom and locates at an antibonding site.