Tunable directional thermal emission using a phase change material-based multilayer structure

The directional and spectral control of thermal emission with a tunable angular range is essential for realizing next-generation smart thermal emitters. However, existing photonic strategy-based thermal emitters manage thermal emission only over a fixed angular range. Here, we present a lossless chalcogenide phase change material (PCM)-based tunable multilayer structure as a thermal emitter for actively regulating angular selectivity in thermal emission. We develop a tunable multilayer stack with a thickness of 1.35 μm by layering alternating thin films of SiO₂ and a high-crystallization-temperature PCM, such as Sb₂S₃. The principle underlying the proposed tunable directional control of thermal emission relies on the tunable Brewster mode within the SiO₂-Sb₂S₃ multilayer cavity. For p-polarized light, the cavity exhibits maximum emissivity across a broad spectral band (10-18 μm) around the Brewster angle. In particular, a peak emissivity of over 95% is achieved in this broad spectral band at the Brewster angle. The angular range of maximum thermal emission can be tuned through the non-volatile structural phase transition property of Sb₂S₃, while maintaining a constant spectral bandwidth. Moreover, we demonstrate electrically controlled thermal emission using a microheater-integrated Sb₂S₃-SiO₂ multilayer cavity. This photonic structure could serve as a versatile, tunable, lithography-free platform to dynamically control the angular range of directional thermal emission and emissivity for emerging applications of thermal emitters.