Mid-IR localized surface plasmon resonances (LSPR) have been demonstrated in nano-ribbons of highly Si-doped InAsSb alloys on GaSb substrates. We show that the slow, steady and selective oxidation of GaSb in water leads to an all-semiconductor mid-IR pedestal configuration consisting of highly doped InAsSb plasmonic resonators on top of GaSb pedestals embedded in an amorphous oxide layer. The homogeneity of the pedestal structure is imaged with an attenuated-total reflection Fourier transform infrared (ATR-FTIR) microscope by measuring around the plasmonic excitation at the plasma wavelength of 5.5 µm. As the plasmonic properties are influenced by modifications of the surrounding medium, we show for all-semiconductor gratings with defined doping level and defined grating geometry, that the GaSb oxidation process allows post-fabrication targeting of mid-IR plasmonic resonances to cover the mid-IR range from 5 to 20 µm. Additionally the pedestal formation reduces the refractive index mismatch between the two interfaces of the plasmonic resonators which allows to exploit a second plasmonic peak and which favors plasmonic field enhancement at the top (air-) side of the structure relevant for enhanced molecular vibration spectroscopy.

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