  Thermal stability of hydrogenated amorphous Si/Ge multilayers has been
investigated by Scanning Electron Microscopy (SEM), Transmission Electron
Microscopy (TEM) and Small-Angle X-Ray Diffraction (SAXRD) techniques.
Amorphous H-Si/Ge multilayers were prepared by RF sputtering with 1.5 and 6
ml/min H2 flow-rate. It is shown by Elastic Recoil Detection Analysis (ERDA)
that the hydrogen concentration increased by increasing H2 flow-rate. Annealing
of the samples was carried out at 400 and 450 oC for several hours. It has been
observed that samples prepared with 6 ml/min flow-rate at both annealing
temperatures underwent significant structural changes: the surface of the
samples was visibly roughened, gas bubbles were formed and craters were
created. The decay of the periodic structure of Si and Ge layers in these types
of multilayers was faster than in non-hydrogenated samples. Samples prepared
with 1.5 ml/min flow-rate have similar behaviour at 450 oC, but at 400 oC the
decay of the first order SAXRD peaks was slower than in case of the
non-hydrogenated multilayers. Qualitatively the observed behaviour can be
explained by the fast desorption of the saturated hydrogen, leading to the
formation of bubbles and craters at 450 oC, as well as, at 400oC in the sample
with lower H-content, by the possible passivation of the dangling bonds
resulting in a slowing down of the diffusion intermixing.
