Porosity Gradient Resulting from Localised Formation of Porous Silicon: The Effect on Waveguiding

Abstract

Porous silicon formation on patterned substrates leads to a depth-dependent porosity. These porosity variations depend on the anodisation parameters and on the size of the open windows in the masking layer. During the anodisation at a constant current intensity, the interfacial reaction area increases and consequently the porosity decreases. Moreover, the porous silicon growth rate depends on crystallographic directions and induces a porosity gradient along the core/cladding interface. These porosity gradients could be crucial in some applications such as optical waveguides. Oxidised porous silicon waveguides were fabricated through a masking layer by applying two constant current intensities during anodisation. The measured near field distribution reveals that the light propagation is localised near the core/cladding interface. These observations confirm that a porosity gradient exists along vertical cross section of waveguides. This study deals with the porosity gradient estimations resulting from the electrochemical etching through an opened window in a masking layer.