Theoretical ab-initio calculations (including both the Configuration Interaction and Density Functional approaches) are used to describe some of the critical surface reactions during plasma enhanced chemical vapor deposition of amorphous and micro-crystalline silicon films. The energetics as well as the reaction mechanism are calculated for the abstraction of surface hydrogen by incident silyl and hydrogen radicals. Another important reaction involving the insertion of these radicals (silyl and hydrogen) into strained Si-Si bonds on the surface is also evaluated. Experiments involve surface topology evolution studies of plasma deposited a-Si:H films using atomic force microscopy (AFM) as well as structural and electrical characterization of silicon dioxide films using several techniques including infrared spectroscopy, ellipsometry, and current-voltage measurements. A predictive kinetic model to describe the growth of silicon films from a predominantly silyl radical flux is developed to explain experimental observations regarding the properties of plasma deposited amorphous silicon films. The model explains diffusion length enhancements under certain processing conditions as well as lays a foundation for understanding the Si-Si network formation during the deposition of a-Si films.