Effects of the nearest neighbors and the alloy matrix on SiH stretching vibrations in the amorphousSiOr:H (0<r<2) alloy system

Hydrogenated silicon suboxides, ${\mathrm{SiO}}_{\mathrm{r}}$:H, for alloy range (0<r<2) have been deposited by remote plasma-enhanced chemical vapor deposition (remote PECVD) under conditions in which hydrogen is incorporated predominantly in monohydride or SiH bonding configurations. We have investigated both the SiH bond-stretching and bond-bending absorption bands by infrared (ir) absorption spectroscopy as a function of r, the alloy composition. In this paper, we have focused on the bond-stretching absorption bands, and have modeled the shape of the bond-stretching band as a function of the alloy composition. There are four distinct local environments for the SiH group in the sub- oxides; these can be written as HSi-${\mathrm{Si}}_{3\mathrm{-}\mathrm{n}}$ ${\mathrm{O}}_{\mathrm{n}}$, for n=0–3. A sum of Gaussian functions, one for each environment, is used to synthesize the absorption in the SiH stretching band. The peak positions of these Gaussians are calculated by an induction model which includes both local and matrix (or alloy) effects; the amplitude weightings are determined from a random statistical model for the local bonding environments of the Si-O groups in the ${\mathrm{SiO}}_{\mathrm{r}}$ alloy. We find that the frequency shifts caused by changes in the matrix, and associated with different values of r, are comparable to the shifts associated with the different local environments. The combination of these effects serves to diminish the discreteness of subband features in the absorption spectrum.