Narrowband diffuse thermal emitter based on surface phonon polaritons

Thermal emission engineering with ability to realize spectral and spatial selection has attracted great attention in recent years. Nanophotonic control of thermal radiation has demonstrated narrowband thermal emitter but with high angle-sensitivity and diffuse thermal emitter but with low quality factor (Q). Here, we demonstrate a simultaneous narrowband, diffuse thermal emitter consisting of 80 nm (<λ/100) thick Ge nanostructures on a silicon carbide (SiC) phononic material. Based on surface phonon polaritons, a spectral coherent emission with a high Q factor of 101 is achieved at ∼10.9 μm wavelength in experiment. Furthermore, this phonon-mediated nanostructure provides spatial control with strong diffuse thermal emission with a full angle at half maximum of 70°. Additionally, the emission wavelength and intensity are tuned by replacing Ge with phase change materials (Ge₂Sb₂Te₅ and In₃SbTe₂). The designed narrowband diffuse thermal emitter offers new perspectives for the engineering of emission and paves the way for infrared applications, including thermal sources, radiative cooling, infrared sensing, and thermal photovoltaics.