Thermally robust ring-shaped chromium perfect absorber of visible light

A number of light-absorbing devices based on plasmonic materials have been reported, and their device efficiencies (or absorption) are high enough to be used in real-life applications. Many light-absorbing applications such as thermophotovoltaics and energy-harvesting and energy-sensing devices usually require high-temperature durability; unfortunately, noble metals used for plasmonics are vulnerable to heat. As an alternative, refractory plasmonics has been introduced using refractory metals such as tungsten (3422°C) and transition metal nitrides such as titanium nitride (2930°C). However, some of these materials are not easy to handle for device fabrications owing to their ultra-high melting point. Here, we propose a light absorber based on chromium (Cr), which is heat tolerant due to its high melting temperature (1907°C) and is compatible with fabrication using conventional semiconductor manufacturing processes. The fabricated device has >95% average absorption of visible light (500-800 nm) independent of polarization states. To verify its tolerance of heat, the absorber was also characterized after annealing at 600°C. Because of its compactness, broadband operational wavelength, and heat tolerance, this Cr perfect absorber will have applications in high-temperature photonic devices such as solar thermophotovoltaics.