Refractive index change in porous silicon after detaching from the substrate

Porous silicon technology offers a simple, wide dynamic range technique for tuning the refractive index of silicon in multilayer structures. However, the refractive index values are very sensitive to fabrication parameters, oxidation and other factors. In this work we investigate some possible causes of refractive index change in porous silicon (PS) fabricated by electrochemical etching of silicon in hydrofluoric acid (HF). The index change is monitored through the wavelength shift in the response of Bragg Reflectors Multilayer Porous Silicon. A shift in the response towards shorter wavelengths was observed after the porous silicon thin film was detached from the silicon substrate. This shift is attributed in part to oxidation due to PS large surface area, and also to stresses inside the material after releasing the thin film from the substrate; these factors have been studied and possible solutions have been suggested.