Near unity narrowband infrared thermal emitters on silicon with silicon carbide-germanium metasurfaces

Traditional thermal emitters are characterized by an incoherent broadband emission spectrum. However, narrowband coherent thermal emission with a high-quality factor in thermally stable materials is highly desirable for applications such as sensing, thermal energy management, thermophotovoltaic systems, and other infrared technologies. Recent advances in engineered nanostructured polaritonic materials, particularly polar dielectric materials in the mid-infrared (MIR) regime, have enabled new approaches to tailoring narrowband coherent thermal emission. The use of low-loss phonon polaritons in thermally stable silicon carbide provides a promising route to MIR thermal emission. In this work, we demonstrate narrowband, near-unity MIR thermal emission by coupling coherent surface phonon polaritons in a SiC layer with a subwavelength germanium grating on a silicon substrate. The demonstrated polarization-dependent thermal emitter, compatible with silicon fabrication technologies for seamless on-chip photonic integration, exhibits narrowband high emissivity (>90%) at a wavelength of ∼11 μm. Furthermore, we show that these emitters achieve experimental quality factors well above 100 while maintaining significant emission across a wide range of incident angles for MIR radiation.