All-semiconductor plasmonic metamaterials for mid-infrared perfect absorption and selective thermal emission

IntroductionSince the advent of metamaterial science, resonant perfect absorbers (PA) with sub-wavelength thickness have been of interest for electromagnetic wave control in various spectral ranges [1]. Perfect absorbers are... [ view full abstract ]

Introduction

Since the advent of metamaterial science, resonant perfect absorbers (PA) with sub-wavelength thickness have been of interest for electromagnetic wave control in various spectral ranges [1]. Perfect absorbers are based on suppressed transmission due to a metallic ground plane and simultaneous suppression of the reflected beam, by impedance matching to free space owing to effective material parameters [2]. In this work, we present PA metamaterials using a layer system of dielectric and highly doped semiconductor (HDSC) materials. Plasmonic and cavity resonances can be excited in this layer system when the topmost layer is patterned with nanoantennas. The strong absorptivity is equal to good thermal emission properties, making the perfect absorbers ideal candidates for narrowband selective thermal sources.

Methods

InAsSb:Si/GaSb/InAsSb:Si layer structures were grown lattice-matched by solid-source molecular beam epitaxy. The topmost layer was patterned using UV or laser interference lithography followed by reactive ion etching (ICP-RIE) and wet chemical etching to obtain a sharp interface between the HDSC and the dielectric spacer. The PA samples were characterized by FTIR spectroscopy in reflectance and transmission mode. The experimental results were corroborated by electromagnetic simulations using the rigorous coupled wave analysis (RCWA). Furthermore, the thermal emission of the PA samples was measured.

 Results and discussion

We evaluate the thickness of the spacer layer as one of the key parameters to determine the interaction of the plasmonic and cavity resonances supported by the structure. Structures with different spacer thicknesses were optically characterized before and after fabrication of the nanoantennas. For an adapted spacer thickness, reflectivity as low as 0.5% is achieved. In addition, PA structures were tested as highly sensitive surface enhanced infrared absorption (SEIRA) spectroscopy substrates, using 20 nm thin films of polymethyl-methacrylate (PMMA) as test analyte. Finally, we show that the emissivity deduced from the thermal emission spectra of the samples is in agreement with Kirchhoff’s law compared to the samples’ reflectivity. Based on these results, we propose a novel surface enhanced sensing technique using the thermal emission of the near-perfect absorbers.

References

[1] Watts et al. Adv. Mater. 2012, 24, OP98-OP120.

[2] Landy et al. PRL 2008, 100, 207402.