Ellipsometric study of the porous silicon: The impact of decoration and oxidation on porosity depth profiling

•Multiple-angle-of-incidence ellipsometric studies reveal a subsurface thin film of modified porous silicon (PSi) with higher porosity compared to the initial layer.•Isopropyl alcohol decoration leads to a decrease in the refractive index and slight thickness increase of the modified PSi film.•Ongoing PSi oxidation in atmospheric conditions causes a gradual decrease in the refractive index of the modified film over several months.•Ellipsometric analysis specifically reveals that the PSi samples subjected to high-temperature annealing exhibit incomplete oxidation, characterized by an oxidized layer thickness significantly smaller than the overall thickness of the PSi samples. The multiple-angle-of-incidence ellipsometric studies of the decoration by isopropyl alcohol of porous silicon (PSi) have been performed. The existence of a subsurface thin film of modified PSi with 5–7 % higher porosity contrary to the initial PSi layer was established. The refractive index and thickness of the film were calculated in the single-layer reflective system model. It was found that empty pores of the film after the sample was kept in isopropyl alcohol for 24 h were filled by its molecules. Thus, the effective refractive index of the modified film decreased while its thickness slightly increased. The refractive index decrease of the film over time during several months of observation is the result of the continuation of the PSi oxidation in atmospheric conditions. The work also presents the results of the PSi samples' oxidation degree by the ellipsometric method after high-temperature annealing in dry air (T = 1000 °C).