Oscillator strength and effective charge in amorphous silicon carbon alloy

In the present paper we will present IR optical absorption data on the Si–C stretching of a-Si1−xCx films for x in the range 0.05≤x≤0.5. Taking into account the variation of the film density upon alloying, we are able to determine the absorption coefficient throughout the composition range. From the integrated absorption of the Si–C stretching band the oscillator strength and the effective charge are calculated. We found that the relation between integrated absorption and number of Si–C bonds is not linear. The proportionality factor A relating these two quantities increases on increasing carbon concentration. This behavior is of great importance for the IR analysis of these materials. The “constant” A is related to the effective charge of the mode, which in turn decreases with increasing carbon concentration. The physical origin of this effect is given. Finally, the effect of hydrogen on the effective charge is analyzed.