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As-growth and Annealing Porous Silicon Mirrors for Optical Applications in the UV: Features for its possible use as Optical Sensor

Abstract This work presents a study of the evolution of the reflectance spectra of porous silicon as-growth and with thermal oxidation under controlled conditions. Porous silicon layers were prepared by electrochemical anodization of a silicon substrate p+ in an aqueous solution of hydrofluoric acid and ethanol. Multilayer structures were formed on the basis of porous silicon, two different layers were realized by controlling the refraction index of each one of the layers using the Bruggemann model, in this case for multilayer as-growth, and subsequently a dry oxidation was performed to observe the change in refractive index and reflectance. A model that contains the refractive index of silicon, air and silicon oxide is used for predicting the behavior of the reflectance spectra. With this model is possible to control the width of the reflectance spectrum of the band pass or also called Distributed Bragg Reflector (DBR), DBR were characterized and measured by SEM and UV-VIS spectroscopy. Reflectance spectra were obtained and we can see that the annealing provoked a shifted towards the ultra violet (UV). These changes on reflectance and refractive indexes indicate that oxidation processes can modify the multilayer porous silicon. The optical band gap energy (Eg) was obtained from 4.36 to 3.98 eV to the DBR. These low cost devices open the way to the development of optical sensing in UV entirely based on silicon.