Thermal Stability and Optical Behavior of Porous Silicon and Porous Quartz Photonic Crystals for High-Temperature Applications

This work investigates the changes in the optical response of photonic crystals based on porous silicon (PSi) as a function of temperature. Using the transfer matrix method in combination with thermo-optical properties, we numerically calculate the optical response of two types of photonic crystals: Distributed Bragg Reflectors (DBRs) and Fabry-Perot microcavities (FPMs). The results reveal that the photonic bandgap shifts with increasing temperature and pressure, with the defect mode in the microcavity notably shifting to longer wavelengths as the temperature rises. Additionally, we explore the transformation of PSi into porous quartz (PQz) via thermal oxidation, which preserves the porosity and multilayer structure, while altering the chemical composition. This results in geometrically identical photonic systems with distinct chemical properties, offering enhanced stability. Our simulations show that PSi structures exhibit a redshift in the photonic bandgap due to thermal expansion, while PQz structures remain optically stable even at elevated temperatures. This work highlights the potential of PQz as a robust material for high-temperature photonic applications, with tunable optical properties and stable performance under extreme conditions. The findings emphasize the feasibility of using porous-silicon-based photonic crystals for advanced optical devices in harsh environments.