On the nanostructure of pure amorphous silicon

New features of the nanoscale structure of amorphous (a)-Si produced by ion-implantation-induced amorphization of crystalline (c)-Si have been determined by the technique of small-angle x-ray scattering (SAXS). Si ion energies up to 17 MeV were used to generate a thick amorphous layer (8 µm) on a c-Si wafer to enable the SAXS measurements. As-implanted and thermally annealed (up to 540 ³C) a-Si were studied. No nanovoids were detected within a sensitivity of 0.1 vol %, but the atomic-scale structure produced a measurable diffuse scattering signal that decreased with increasing anneal temperatures. These measurements show that the known density deficit of 1.8% in a-Si relative to c-Si cannot be due to voids and that a-Si is homogeneous on nm length scale.