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-Si) and standard device-quality plasma-grown a-Si: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-Si:H with respect to the H-implanted sample. We discuss qualitative resemblances and quantitative differences of the structural evolution of H-implanted a-Si and a-Si:H in terms of H solubility and defect structure in a-Si. In addition, the study of a-Si implanted with H at different concentrations shows that the amount of H nanoclustering increases superlinearly with the concentration of H atoms exceeding solubility.