Far-field thermal emission from a semiconductor hyperbolic metamaterial.

Abstract

This paper investigates the far-field thermal emission of a Si:InAs/AlSb semiconductor hyperbolic metamaterial (HMM). Understanding the thermal emission of HMMs could result in advancements in thermophotovoltaics and thermal emission management. In recent years, there has been controversy about whether the large wavevector volume plasmon polariton (VPP) modes that exist in HMMs could be outcoupled into the far field using a grating and give rise to super-Planckian thermal emission. In this experiment, gold gratings with varying periods were applied to the surface of the HMM to outcouple the VPP modes into free space. The sample was heated to 185°C, and the polarized thermal emission was measured using Fourier transform infrared spectroscopy. The HMM showed minimal angle sensitivity up to 50°. The sample showed multiple peaks in emission which corresponded to the resonant wavelengths of the VPP modes, demonstrating outcoupling from these modes. Although these modes showed increases in the emissivity, super-Planckian emission was not observed. Emission from VPP modes could be leveraged to create materials with designer emissivity profiles.