Infrared absorption spectra of SiO2 precipitates of various shapes in silicon: calculated and experimental

Abstract

It is shown that the infrared absorption band at 1230 cm-1, observed under certain conditions of oxygen precipitation in silicon, is the LO mode of SiO2. The LO mode, which is normally infrared inactive, becomes infrared active under the condition of polarization of small (<0.36 μm) platelets in an appropriate dielectric matrix (silicon). Infrared absorption spectra of SiO2 particles of various shapes, imbedded in silicon, have been calculated. For platelet SiO2 precipitates, the spectrum shows an absorption band at 1215 cm-1, which is reasonably close to the observed band at 1230 cm-1. For SiO2 precipitates of other shapes the spectra do not exhibit this absorption band. Instead, they exhibit a slightly weaker primary absorption band at 1095 cm -1, the TO mode, and a very weak band at 1170 cm-1, which is a mixed mode of longitudinal and transverse optical phonons.