Far-field thermal emission from a semiconductor hyperbolic metamaterial.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanophotonics

Background:

• Hyperbolic metamaterials (HMMs) exhibit unique electromagnetic properties.
• Controversy exists regarding the potential for super-Planckian thermal emission from HMMs via volume plasmon polariton (VPP) modes.
• Understanding thermal emission from HMMs is crucial for applications in thermophotovoltaics and thermal management.

Purpose of the Study:

• To experimentally investigate the far-field thermal emission of a Si:InAs/AlSb semiconductor hyperbolic metamaterial (HMM).
• To determine if VPP modes in HMMs can be outcoupled to the far field to achieve super-Planckian thermal emission.
• To explore the potential of HMMs for creating materials with tailored emissivity profiles.

Main Methods:

• Fabrication of a Si:InAs/AlSb HMM.
• Application of gold gratings with varying periods to the HMM surface to facilitate VPP mode outcoupling.
• Measurement of polarized thermal emission using Fourier transform infrared spectroscopy at elevated temperatures (185°C).

Main Results:

• The HMM exhibited minimal angle sensitivity in its thermal emission up to 50°.
• Multiple emission peaks were observed, correlating with the resonant wavelengths of VPP modes, confirming their outcoupling.
• Despite increased emissivity due to VPP modes, super-Planckian thermal emission was not achieved.

Conclusions:

• The experimental results demonstrate the outcoupling of VPP modes from semiconductor HMMs into free space.
• Super-Planckian thermal emission was not observed under the experimental conditions.
• The findings suggest that VPP modes can be utilized to engineer materials with designer emissivity characteristics for advanced thermal management and energy applications.