Silicon rich silicon oxide films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The films were doped in situ using an organometallic precursor. Optical measurements show that the refractive indices of the films are determined by the silane to oxygen flow rate ratio used during the depositions. The erbium content as measured by elastic recoil detection (ERD) is also strongly dependent on the oxygen flow rate, with more erbium being incorporated in the more highly oxygenated films. The erbium content was also found to vary inversely with plasma power, which did not have a significant effect on the silicon to oxygen ratio. This allows the erbium and excess silicon levels of the films to be controlled independently.