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 less than or equal t o x less than or equal to 0.5. Taking into account the variation of the fil m density upon alloying, we are able to determine the absorption coefficien t throughout the composition range. From the integrated absorption of the S i-C stretching band the oscillator strength and the effective charge are ca lculated. We found that the relation between integrated absorption and numb er 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 "consta nt" A is related to the effective charge of the mode, which in turn decreas es with increasing carbon concentration. The physical origin of this effect is given. Finally, the effect of hydrogen on the effective charge is analy zed. (C) 2000 Elsevier Science Ltd. All rights reserved.