  The present work is essentially focused on the study of optical and
structural properties of hydrogenated amorphous silicon thin films (a-Si:H)
prepared by radio-frequency cathodic sputtering. We examine separately the
influence of hydrogen partial pressure during film deposition, and the effect
of post-deposition thermal annealings on the main optical characteristics of
the layers such as refraction index, optical gap and Urbach energy. Using the
grazing X-rays reflectometry technique, thin film structural properties are
examined immediately after films deposition as well as after surface oxidation
or annealing. We show that low hydrogen pressures allow a saturation of
dangling bonds in the layers, while high doses lead to the creation of new
defects. We show also that thermal annealing under moderate temperatures
improves the structural quality of the deposited layers. For the films examined
just after deposition, the role of hydrogen appears in the increase of their
density. For those analysed after a short stay in the ambient, hydrogen plays a
protective role against the oxidation of their surfaces. This role disappears
for a long time stay in the ambient.
  Keywords
  Amorphous silicon, Grazing incidence X-rays, Hydrogen, Optical properties,
Penetration depth, Reflectometry, Thermal annealing, Thin films.
  PACS Numbers
  61.10.K - 61.43.D - 68.55.JK - 68.55.81.15.A
