Ellipsometric study of refractive index anisotropy in porous silicon

Porous Si layers of different thicknesses were prepared by anodising p(+)-t ype Si substrates with a resistivity of 0.01 Omega cm. The porosity of the samples ranged from 23% to 62%. The refractive index values for the ordinar y and extraordinary rays were determined by multiple angle of incidence ell ipsometry, from which an optical anisotropy parameter varying from 13% to 2 0% was obtained. The porous Si layers were modelled as uniaxially anisotrop ic films on an isotropic substrate, with an optical axis perpendicular to t he sample surface. The morphological anisotropy which is typical for the p( +) -type porous Si with a predominating cylindrical geometry is responsible for these optical properties. All the porous Si layers studied were found to be optically negative. (C) 1999 Elsevier Science B.V. All rights reserve d.