Structure and correlations in porous silicon studied by X-ray scattering methods

The internal structure of p− and p+ doped porous silicon (PS) has been investigated by small-angle X-ray scattering (SAXS) and grazing incidence diffraction (GID) using synchrotron radiation. The silicon morphology in p− doped samples shows a bimodal distribution of small (some nm) and larger (some 10 nm) particle sizes for all porosities investigated. The diameter of the small particles decreases with increasing porosity, which is accompanied by a blue shift of the luminescence as predicted by theory. In p+ doped PS we found predominantly large cylindrically shaped particles, oriented perpendicular to the surface, forming a perfect lattice with holes. These particles are arranged with preferred lateral distances with a correlation length in the order of their sizes