Porosity gradient resulting from localised formation of porous silicon: The effect on waveguiding

Porous silicon formation on patterned substrates Leads to a depth-dependent porosity. These porosity variations depend on the anodisation parameters a nd on the size of the open windows in the masking layer. During the anodisa tion at a constant current intensity, the interfacial reaction area increas es and consequently the porosity decreases. Moreover, the porous silicon gr owth rate depends on crystallographic directions and induces a porosity gra dient along the core/cladding interface. These porosity gradients could be crucial in some applications such as optical waveguides. Oxidised porous si licon waveguides were fabricated through a masking layer by applying two co nstant current intensities Juring anodisation. The measured near field dist ribution reveals that the light propagation is localised near the core/clad ding interface. These observations confirm that a porosity gradient exists along vertical cross section of waveguides. This study deals with the poros ity gradient estimations resulting fl om the electrochemical etching throug h an opened window in a masking layer.