Determination of the complex refractive index of free-standing porous silicon and oxidized porous silicon in the Visible and Ultraviolet range

Abstract

This work determined the spectral values in the 250–850 wavelength regions of the complex refractive index, n and k, for free-standing porous silicon (PS) and oxidized PS layers. These values were extracted from the experimental reflectance and transmittance spectra. One of the free-standing PS layers was fabricated with high porosity, and the other had low porosity. Thereafter, both layers were oxidized by dry oxidation to achieve a free-standing oxidized PS layer. The oxidation of the porous structures dramatically affects the optical properties of the free-standing layers, especially in the short wavelength Ultraviolet and Visible ranges, since the average transmittance enormously increases, reaching almost 90% at some specific points. Also, we found that the average value of the refractive index and extinction coefficient is higher for PS layers with lower porosity than those with higher porosity. The extinction coefficient and refractive index values are further reduced by oxidizing the free-standing PS layers in the 250–850 wavelength region. The reader can see a zero extinction coefficient value for the oxidized PS layer manufactured with high porosity. Our results show that due to a dry oxidation process in an air environment, the absorption coefficient can be reduced until reaching a value of zero. Due to that, it could be possible to design photonic crystals such as Microcavities, Fibonacci structures, waveguides, and Rugate filters without optical losses caused by light absorption in the Ultraviolet and Visible regions. Pore diameter, thickness and Energy-dispersive X-ray spectroscopy (EDS) elemental spectrum of two different PS layers were determined.