LIGHT-SCATTERING FROM POROUS SILICON

Light scattering from porous silicon Layers has been investigated. It reveals that scattering depends strongly, first, on the layer thicknes s and secondly on the doping level of the substrate. During the format ion of porous silicon (PS) on p-type Si material, the bottom of the PS layer develops a roughness which is responsible for the observed scat tered light. The two other possible contributions to the scattering, t he bulk PS and the interface between PS and air were found to be negli gible (< 1%) compared with the first one and independent of the layer thickness. Mechanical roughness and optical scattering measurements gi ve a bottom interface flatness of the order of 100 Angstrom per micron of layer and a mean lateral spatial frequency of the oscillations of 1 mu m(-1), independent of the sample thickness. In contrast the back interface of layers from a heavily doped p + substrate remains almost hat and the level of scattering is low.