Characterization of hydrogen-like states in bulk Si_1-xGe _x alloys through muonium observations

Much of our knowledge of the charge states, lattice site and behaviour of hydrogen in bulk semiconductors comes from observation of its muonium analogue. Here we present studies of muonium behaviour across the composition range in bulk, Czochralski-grown Si_1-xGe_x alloy material, focusing in particular on the muonium hyperfine parameters. For the bond-centred muonium species, a broad distribution of parameters is observed, consistent with a variety of bonding environments. The average value of the isotropic component of the bond-centred hyperfine parameter shows a linear variation with alloy composition, which might be expected based on the linear variation with composition of alloy bond lengths. In contrast, the hyperfine parameter of the tetrahedral-site muonium species (Mu_T) appears to vary non-linearly with alloy composition, and an explanation of this in terms of Mu_T mobility is provided. The temperature dependence of the Mu_T hyperfine parameter observed in several alloy compositions is compared with that seen in pure Si. Previous descriptions of the low-temperature behaviour of the Mu _T parameter in Si are discussed in the light of results from Si _1-xGe_x material.