Development of Polycrystalline Silicon Based Photonic Crystal Membrane for Mid-Infrared Applications

Free-standing polycrystalline silicon (Si) based photonic crystal (PhC) membranes with etched circular and square holes are developed to display high reflectivity in the mid-infrared (MIR) region. Greater than 90% reflection was measured in the MIR wavelengths around 3.58 μm. By using square air holes in the PhC membrane, the mechanical strength of the polycrystalline Si membrane can be enhanced as square air holes have a lower filling factor of 36% of air holes, compared to 49% in circular air holes while keeping the reflectance around 3.45 μm more than 90%. Such Si PhC membranes offer opportunities for specific applications like filters. To illustrate the feasibility of such devices, simulation works are done by configuring two Si PhC membranes to create a Fabry-Perot interferometer operating in MIR region. The filtered peak shows a full width half maximum of 0.08 nm which corresponds to a quality factor of around 43800, thus demonstrating the possibility of high-resolution applications such as gas sensing and hyperspectral imaging.