Extended theory for local‐phonon‐coupled low‐energy anharmonic excitation of oxygen in silicon: Calculation of line intensity ratio

Abstract

To describe consistently the energies and the intensities of the infrared absorption lines of oxygen in silicon for the 30, 600, 1100, 1200, 1700, and 1800 cm–1 bands, an original model for the two-dimensional low-energy excitation of oxygen coupled to the A2u local mode has been expanded so as to include the coupling to the A1g local mode. Calculations with the expanded model have reproduced the overall energy levels that describe well the energies of all the absorption lines and the relative oscillator strengths of the main lines at 1205.7 and 648.2 cm–1. The former and the latter are, respectively, caused by the coupling of the two-dimensional low-energy anharmonic excitation to the A2u and A1g local modes. Thus, it is considered that this expanded model has properly taken into account the essential interaction terms. However, the reason for the values of the oscillator strengths calculated for the 1748.6 and 1819.5 cm–1 lines being too small should be clarified.