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

## TL;DR

This study shows how dry oxidation affects the structure and optical properties of porous silicon materials, which could be useful for photonic devices.

## Contribution

The study uniquely links morphology, doping, and oxidation effects to optical performance in mesoporous photonic structures.

## Key findings

- P+ wafers maintain smoother surfaces and higher Si content after oxidation compared to P++ wafers.
- Oxidation causes blue shifts in localized defect modes due to refractive index changes.
- Porous Si–SiO2 structures from P+ wafers show reduced Rayleigh scattering losses and sharper optical modes.

## Abstract

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.