Bimodal size distribution in p−porous silicon studied by small angle X-ray scattering

The structure of free-standing films of p−-doped porous silicon with different porosities has been investigated by small-angle X-ray scattering using synchrotron radiation. The silicon morphology in the samples shows a bimodal distribution of particle sizes for all porosities investigated: small spherically shaped particles with a diameter of a few nanometers and large cylindrically shaped particles oriented with their axis perpendicular to the surface. Fractal structures could not be observed. With increasing porosity the diameter of the small particles decreases and a blue shift in the photoluminescence and absorption is observed which supports the quantum confinement model to explain this behavior.