CALCULATION OF OPTICAL CONSTANTS IN POROUS SILICON THIN FILMS USING DIFFUSED AND SPECULAR REFLECTANCE MEASUREMENT

In this work a method is proposed to calculate the optical constants of porous silicon (PS) thin films. The method is based on the theoretical simulation of the experimental reflectance spectra. In the optical system of this method the PS is considered a homogeneous, absorbing thin film, deposited on a silicon substrate of semi-infinite dimension. The theoretical form of the systems reflectance is calculated using the summation method proposed by Airy. Light scattering is included in the model by introducing the Davies–Bennett relation. The refraction index of the material is fit with the simple harmonic oscillator, proposed by Wemple–DiDomenico. The model was tested on two samples fabricated with anodization times of 25 and 35 min; the values for the refraction indexes, absorption coefficients, thickness and roughness were calculated for both samples. The PS samples were fabricated by electrochemical anodization of single crystal p-type silicon substrates in HF (25%) + isopropyl alcohol solution.