Nanoclustering of hydrogen in ion-implanted and plasma-grown amorphous silicon

We report a systematic study of small-angle x-ray scattering and Raman spectroscopy on hydrogen-implanted amorphous silicon $(a-\mathrm{Si})$ and standard device-quality plasma-grown $a-\mathrm{S}\mathrm{i}:\mathrm{H},$ both having a hydrogen concentration of 11 at. %. The modifications of short-range and medium-range structural order induced by annealing are investigated. We find that annealing causes the formation and growth of nanoscale H complexes in both materials. However, the volume content of the H nanoclusters is strongly influenced by the disorder in the original structure, remaining smaller by a factor of 3 in the $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ with respect to the H-implanted sample. We discuss qualitative resemblances and quantitative differences of the structural evolution of H-implanted $a-\mathrm{Si}$ and $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ in terms of H solubility and defect structure in $a-\mathrm{Si}.$ In addition, the study of $a-\mathrm{Si}$ implanted with H at different concentrations shows that the amount of H nanoclustering increases superlinearly with the concentration of H atoms exceeding solubility.