Wavelength-tunable mid-infrared thermal emitters with a non-volatile phase changing material.

The ability to continuously tune the emission wavelength of mid-infrared thermal emitters while maintaining high peak emissivity remains a challenge. By incorporating the nonvolatile phase changing material Ge ₂ Sb ₂ Te ₅ (GST), two different kinds of wavelength-tunable mid-infrared thermal emitters based on simple layered structures (GST-Al bilayer and Cr-GST-Au trilayer) are demonstrated. Aiming at high peak emissivity at a tunable wavelength, an Al film and an ultrathin (∼5 nm) top Cr film are adopted for these two structures, respectively. The gradual phase transition of GST provides a tunable peak wavelength between 7 μm and 13 μm while high peak emissivity (>0.75 and >0.63 for the GST-Al and Cr-GST-Au emitters, respectively) is maintained. This study shows the capability of controlling the thermal emission wavelength, the application of which may be extended to gas sensors, infrared imaging, solar thermophotovoltaics, and radiative coolers.