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 scatt ering using synchrotron radiation. The silicon morphology in the sampl es shows a bimodal distribution of particle sizes for all porosities i nvestigated: small spherically shaped particles with a diameter of a f ew nanometers and large cylindrically shaped particles oriented with t heir axis perpendicular to the surface. Fractal structures could not b e observed. With increasing porosity the diameter of the small particl es decreases and a blue shift in the photoluminescence and absorption is observed which supports the quantum confinement model to explain th is behavior.