This paper discusses the bonding of H atoms in a-Si1−xGex: H alloys that are deposited in a dual magnetron sputtering system. The relative numbers of SiH and GeH bonds, as a function of the Ge content are found to be qualitatively different than in films (a) grown by the glow discharge (GD) decomposition of germane, silane mixtures, or (b) deposited in diode sputtering (DS) systems with Ge/Si targets. The intrinsic films deposited by magnetron sputtering display higher concentrations of bonded H in monohydride arrangements and higher majority carrier photoconductivities than either the GD or DS alloy films. These differences are explained in terms of a model for H atom incorporation which emphasizes the relative importance of surface and plasma phase chemical interactions. In the magnetron films, H atom bonding is primarily determined by surface reactions, whereas in the other two techniques plasma phase chemistry is the dominant factor which favors precursors with SiH rather than GeH bonds.