Hydrogen behaviour in bulk Si_1-xGe_x alloys as modelled by muonium

Si_1-xGe_x alloys have been the subject of much attention over the past decade due to their ability to provide new electrical properties and functionality whilst using existing silicon device fabrication technology. Here we are concerned with the behaviour of isolated hydrogen in bulk alloy material, as modelled by its pseudo-isotope muonium. In particular, hyperfine parameters of muonium species are determined; for the bond-centred state, a broad distribution of hyperfine constant is found, consistent with a variety of different bonding environments within the alloy, but with the average value showing a linear variation with alloy composition. The ionisation behaviour of the bond-centred species is also modified in low-Ge material compared with that seen in Si. The tetrahedral muonium species shows a lower than expected hyperfine parameter in low-Ge alloy material. Comparison with the known behaviour of hydrogen in Si and Ge when isovalent impurities are present is also made.