Photoconductive hydrogenated amorphous silicon films were deposited by ion-beam-assisted evaporation using a hydrogen-argon plasma. The plasma source was used to generate the ion beam which was accelerated by a moderate substrate bias (U = 20 V). The influence of the substrate temperature was studied between 100 and 500 degreesC. The hydrogen bonding configurations were obtained from infrared spectrometry experiments. The effusion of hydrogen and of argon was followed by thermal desorption spectrometry. It was demonstrated that an increase of the substrate temperature produces a densification of the material, which has a great influence on the stability of hydrogen and on the photoconductivity. The optical parameters, such as the optical gap and the refractive index are correlated to the structure evolution.