Films of a-Si:H have been prepared in a vacuum deposition system both with and without the help of low energy ion beam bombardment. Water vapour was introduced into the system in order to determine how it is incorporated into the Si film and to observe the effects of the ion beam on this process. Silane was used as the feed gas for the ion source and the ion beam enabled the oxygen to form only the bridging configuration between Si atoms. Without the ion beam, three oxygen related absorption peaks are obtained in the infrared spectrum. Water-free films of a-Si:H were prepared to investigate the effects of ion beam voltage, ion beam intensity and substrate temperature on the resulting film photoconductivity. These parameters are interrelated and a maximum in the photosensitivity is found for rather narrow ranges of these parameters.