Effect of Dry Oxidation on the Optical Response and Morphology of Mesoporous Hybrid Structures

This work presents a detailed experimental and theoretical investigation of periodic and quasiperiodic hybrid photonic structures composed of porous silicon (PS) and thermally oxidized porous Si-SiO₂. Designed with a Fibonacci sequence and embedded between asymmetric Bragg mirrors, the structures were fabricated via electrochemical etching on p-type (100)-oriented silicon wafers with distinct doping levels (P⁺ and P⁺⁺). A two-step dry oxidation process (350 °C and 800 °C) was employed to stabilize the porous network and transform PS into a robust hybrid Si-SiO₂ matrix. SEM and EDS analyses revealed that wafer doping significantly affects morphology, oxide growth, and silicon retention, with P⁺-based structures maintaining smoother surfaces and higher Si content postoxidation. Optical transmission spectra revealed that oxidation induces substantial blue shifts in localized defect modes, resulting from changes in refractive index and optical path length. Notably, porous Si-SiO₂ structures fabricated from P⁺ wafers exhibit sharper and less attenuated localized modes compared to those from P⁺⁺ wafers, due to reduced Rayleigh scattering losses. Scattering loss estimations corroborate these findings. This study uniquely correlates morphology, doping, and oxidation kinetics to optical performance, demonstrating that dry oxidation can be strategically employed to enhance light confinement and reduce optical losses in mesoporous Fibonacci-based photonic structures. These results position porous Si-SiO₂ hybrid systems as promising platforms for low-loss photonic devices, sensors, and microcavity-based applications.