Anharmonic local vibration of carbon in crystalline silicon.

In order to investigate the anharmonicity in the local vibration of the substitutional carbon (Cs) impurity in silicon crystal, we have carried out infrared absorption experiment for the higher harmonic absorption line associated with the fundamental one at 605 cm-1. To detect weak higher harmonic absorption, we adopted the cast-grown multicrystalline silicon for solar cell fabrication, whose Cs concentration is extraordinary high compared with the silicon crystals for microelectronic devices. The thickness of the samples was optimized so that the small spectral structure can be well distinguished. Although the second harmonic line at 1206 cm-1 has been well observed, we found no other higher harmonic lines of observable intensity. We thus conclude that the local vibration of the Cs in silicon is dominated by the third order anharmonicity only, with negligibly weak fourth anharmonicity, in contrast to the case of well-investigated CaF2:H. The energies of the fundamental and second harmonic lines, together with the line intensity ratio, have been explained consistently by the model that took into account the third anharmonic potential. [ABSTRACT FROM AUTHOR]