  Amorphous hydrogenated silicon (a-Si:H) is an important material for surface
defect passivation of photovoltaic silicon (Si) wafers in order to reduce their
recombination losses. The material is however unstable with regards to hydrogen
(H) desorption at elevated temperatures, which can be an issue during
processing and device manufacturing. In this work we determine the temperature
stability of a-Si:H by structural characterization of a-Si:H/Si bilayers with
neutron- (NR) and X-ray reflectometry (XRR) combined with photoconductance
measurements yielding the minority carrer lifetime. The neutrons are sensitive
to light elements such as H, while the X-rays which are insensitive to the
H-concentration, provide an independent constraint on the layer structure. It
is shown that H-desorption takes place at a temperature of approximately T =
$425\,^{\circ}\mathrm{C}$ and that hydrogen content and minority carrier
lifetimes have a strongly correlated linear relationship, which can be
interpreted as one hydrogen atom passivating one defect.
