Thermal darkening of one-dimensional photonic crystal containing tellurium suboxide

The purpose of this study is to experimentally and theoretically evaluate the optical properties of a one-dimensional photonic crystal (PC) with a defect layer before and after an annealing procedure. A sputtering technique with high index (TeOx) and low index (SiO2) materials was used to fabricate the 1D PC with a defect layer. The chemical and structural analysis of a single layer TeOx thin film was evaluated by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD). The optical constant of the single layer was also determined based on the envelope method from transmittance spectra measured by ultraviolet visible near-infrared spectrophotometry (UV-VIS-NIR). The measured reflectance spectra of the 1D PC were compared with the results simulated using the transfer matrix method (TMM) before and after the annealing procedure. A photonic bandgap (PBG) appears within the desired, near-infrared (NIR), region. The defect mode in the 1D PC was observed at lambda = 1455 nm within the PBG of lambda = 1235-1723 nm (Delta lambda = 488 nm). The reflectance spectra overall shifted toward longer wavelength due to thermal darkening effect resulting from the thermally induced optical property changes.