Porosity depth profiling of thin porous silicon layers by use of variable-angle spectroscopic ellipsometry: a porosity graded-layer

Variable-angle spectroscopic ellipsometry was used to determine nondestructively the porosity depth profile and thickness of thin porous silicon layers produced by anodization of p(+)-doped silicon wafers. A porosity graded-layer model is presented and used in the analysis of the material. In the porosity graded-layer model an inhomogeneous layer is built up by several thin sublayers with the porosity changing slightly from one sublayer to the next. Results from the ellipsometry analysis and from transmission electron microscopy reveal inhomogeneous layers whose porosity and thereby optical properties change with their depth in the layers. (C) 1998 Optical Society of America.