Ellipsometry studies on the effect of etching time in porous silicon

The optical response of n-type porous silicon is investigated using spectroscopic ellipsometry in the energy range of 1.5–View the MathML source. The close interrelationship between the microstructure and electronic states is examined on (1 0 0) oriented n-type single crystal silicon wafers anodically etched for different durations under illumination with a halogen lamp. Changes occurring in the pseudodielectric response upon etching are analyzed using a multilayer model within the effective medium approximation. Sum rules are used to evaluate changes in the effective number of electrons participating in the optical transition (Neff). The process of etching is shown to result in a substantial shift of spectral weights to the visible region.