An all-dielectric black absorber? A group of researchers from China has recently demonstrated this functionality using a lithography-free and large-scale compatible fabrication route. The efficient harvesting of electromagnetic waves by sub-wavelength nanostructures can result in perfect light absorption in a broad spectral range. Although advances in nanofabrication have provided the opportunity to realize deep sub-wavelength nanounits, the repeatability and upscaling of these routes remained a challenging task. Thus, recently, the concept of lithography-free planar light perfect absorbers has attracted much attention. On the other hand, metals, as the common component used in these absorbers, are prone to oxidation and corrosion under high temperatures and harsh environments, which in turn limits their long-term stability. A dielectric based design could eliminate these deficiencies.

In this paper the authors have addressed both issues using an elegant design. Using a Ge based Fabry-Perot cavity design they achieved an average absorption above 97% with high angular tolerance of up to ±50°. The planar morphology of the design facilitates its adaptation on a flexible platform. Considering the fact that semiconductors (such as Ge) have highly efficient excited state dynamics (compared to metals), this design can potentially be used in many applications including large-scale flexible optoelectronics.

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