Narrow Bandwidth and Tunable Mid-Infrared Thermal Emitter Design Based on Double Asymmetric Dielectric Metasurfaces

Thermal emitters working in the mid-infrared (MIR) region are indispensable in many applications, such as sensing, thermophotovoltaics, and imaging. Resonance wavelength tunability, high efficiency, cost-effectiveness, and high quality (Q) factor are desirable properties of thermal emitters. Selective thermal emitters have been realized using metallic metasurfaces, which, due to ohmic losses, do not exhibit very sharp emission peaks. Recently, metasurfaces possessing very high Q factors made of dielectric materials with asymmetric features that exploit quasi-bound states in the continuum are introduced. The dielectric metasurface-based thermal emitters shown in the literature have a single type of asymmetry, such as a difference in the length of resonators or angular separation of resonators. However, resonance wavelength and thermal emissivity could be tuned by having multiple types of asymmetries. This study proposes a structure consisting of a zigzag array of silicon rectangular bars with different lengths as resonators. Gold is the choice of the substrate with a dielectric layer made of Al2O3 sandwiched between gold substrate and silicon bars. Based on the conducted simulations, an emissivity value exceeding 0.99 with a Q factor of 116 at the resonance wavelength of 5.818 µm was obtained when the silicon bars were separated by π/25 from the origin in opposite directions with a length asymmetry factor of 0.3. Additionally, independent tuning of emissivity intensity and resonance wavelength is displayed. Such findings can lead to bespoke thermal emitter designs.