Abstract

A numerical study has been carried out on optical properties of an absorber made of a natural anisotropic hyperbolic material, subject to normally incident light. The proposed absorber, consisting of an array of pyramidal nanostructures, made from bismuth telluride (Bi₂Te₃, a hyperbolic medium) on the top of a smooth substrate, is submerged in water. The designed absorber was numerically studied by using finite-difference time-domain (FDTD) method and rigorous coupled-wave analysis (RCWA) method. Numerical results show that such an absorber has a perfect absorptance for solar energy in a broadband wavelength range of 300 - 2400 nm by combining the slow-light effect and gradient index effect together. The unique optical property of such absorber contributes to the potential application in solar energy harvesting.

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