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This work reports on the structure of defects around Sn atoms in amorphous germanium-tin alloys deposited by the rf sputtering of compound targets, The influence of atomic hydrogen on the structure of such defects is reported for the first time. Th.e samples were analyzed by Rutherford backscattering spectrometry and conversion electron Mossbauer spectroscopy. The main conclusion of this research is that, besides the known substitutional position of Sn atoms in the a-Ge network, a new Sn bonding configuration appears, which may be at the origin of the degradation of the optoelectronic properties of the alloy found experimentally. This new configuration is an octahedrally coordinated Sn atom resulting from the trapping of Ge vacancies by Sn atoms, the energetically favored final site being the tin atom in the center of the Ge relaxed divacancy.

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