Fabrication of a reflective mirror within wide incidence angles for mid-infrared wavelength

One-dimensional (1-D) photonic crystal with photonic band-gap based on porous silicon is fabricated with alternative etching currents during anodization. The microstructure was characterized by scanning electron microscopy and the optical reflectance spectra by Fourier transform infrared spectroscopy. A band-gap centered at 6 microns with a bandwidth of 3 microns has been successfully obtained. The prepared multilayer structure can reflect mid-infrared within a wide incidence angle up to 50deg. After proper oxidation process, its thermal properties can be improved significantly, and meanwhile the band-gap only slightly shifts to that centered at 5.7 microns. PECVD of Si₃N₄ is employed to improve the surface morphology in order to make the structure suitable to the fabrication of sensors. It is found that deposition of Si₃N₄ does not change the reflectance properties of the structures.