Hydrogen release in annealed hydrogenated a-Si/a-Ge multilayers

A combined study of hydrogenated sputtered single a-Si and a-Ge layers and a-Si/a-Ge multilayers (MLs) has been carried out in order to establish the reasons of H release and associated structural degradation of the MLs when they are submitted to annealing. ERDA analysis of the single layers of a-Si and a-Ge shows that H escapes from the layer much more efficiently in a-Ge than in a-Si. This agrees with IR absorbance measurements on the MLs showing that the Ge-H signal disappears at a lower annealing time (for a given annealing temperature) than Si-H and Si-H2 do. The conclusion is drawn that the structural degradation of a- Si/a-Ge MLs primary starts with release of H in the Ge layers most probably because of the smaller binding energy of the H-Ge bond and the greater weakness of the Ge lattice.