Abstract
Infrared absorption spectroscopy remains a challenge due to the weak light-matter interaction between micron-wavelengthed infrared light and nano-sized molecules. A highly doped semiconductor supports intrinsic plasmon modes at infrared frequencies, and is compatible with the current epitaxial growth processing, which makes it promising for various applications. Here, we propose an all-semiconductor plasmonic resonator to enhance the infrared absorption of the adsorbed molecules. An optical model is employed to investigate the effect of structural parameters on the spectral features of the resonator and the enhanced infrared absorption characteristics are further discussed. When a molecular layer is deposited upon the resonator, the weak molecular absorption signal can be significantly enhanced. A high enhancement factor of 470 can be achieved once the resonance wavelength of the resonator is overlapped with the desired vibrational mode of the molecules. Our study offers a promising approach to engineering semiconductor optics devices for mid-infrared sensing applications.
Highlights
Infrared (IR) spectroscopy of the distinct vibrational and rotational molecular resonances provides a powerful tool for the analysis and characterization of a wide range of molecules [1,2,3]
We proposed an all-semiconductor plasmonic resonator with Fabry-Perot–like resonance to enhance the infrared absorption of the molecules
To explore the possible application of the proposed resonator in surface-enhanced infrared absorption spectroscopy (SEIRAS), we considered the electromagnetic coupling between the plasmonic modes and infrared vibrational modes of molecules
Summary
Infrared (IR) spectroscopy of the distinct vibrational and rotational molecular resonances provides a powerful tool for the analysis and characterization of a wide range of molecules [1,2,3]. The wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross-sections of the molecules. This mismatch makes infrared detection and identification of nanoscale volumes of molecules challenging. Many intrinsic plasmonic properties can be masked by the poor metal quality or poor semiconductor-metal interfaces To overcome this problem, an all-semiconductor nanoantenna array utilizing epitaxially grown InAs had been demonstrated for infrared sensing [21]. Strong absorption can be achieved by coupling into the negative-index, highly confined surface plasmon polariton modes in a multilayer epitaxial structure [22]. The enhanced infrared absorption characteristics are further discussed for SEIRAS
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