Modeling of a Highly Optimizable Vertical-Cavity Thermal Emitter for the Mid-Infrared

A device providing narrowband and highly directional mid-infrared (mid-IR) thermal emission was devised and modeled with the goal to provide foundations for the design and define the challenges for the fabrication process. The concept of choice is an aperiodic multilayer stack of dielectric layers (Si and SiO2) on a planar metallic surface acting as a heater. By varying the layer- depths, this design is highly optimizable for individual specifications, especially for enhancing the thermal emittance near to unity around a target wavelength. This work considers stacks with dielectric layers with silica on the top as well as on the bottom. The latter is acting as a vertical resonant cavity. A transfer matrix approach was devised and a proprietary genetic-algorithm toolbox was used to identify highly performant stack configurations. The wavelength- as well as temperature-dependences of all materials were carefully implemented using state-of-the-art dispersion models. Highly efficient thermal emission properties were achieved for several stack configurations, each corresponding to different substrate metals (Ag or W) or layer-depth boundaries.