Pedestal formation of all-semiconductor gratings through GaSb oxidation for mid-IR plasmonics

Abstract

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.

Phosphonate monolayers on InAsSb and GaSb surfaces for mid-IR plasmonics

“…Details on the fabrication can be found in previous work [3,28]. 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-Heptadecafluorononadecylphosphonic acid (Cas N. 625095-76-3) and (6-{2-[2-(2-Methoxy-ethoxy)-ethoxy]-ethoxy}-hexyl)phosphonic acid (Cas N. 1049677-18-0) were synthesized by Sikemia. For the sake of simplicity, in the following, we will call the phosphonic acid with the fluorinated terminate group FDPA and the phosphonic acid with the methoxy-terminated ethylene glycol group EGPA.…”

“…In a long-time air oxidation study, it could be shown that a 3 nm thick native oxide layer appears on GaSb within one day whereas after 3 years this layer increases only moderately by 1 nm [9]. The hydrolytic stability for InAs in neutral water was reported [10], but GaSb oxidizes in an aqueous environment [11,12].…”

Surface-Enhanced Thermal Emission Spectroscopy with Perfect Absorber Metasurfaces

“…To validate the grafting of trimethoxysilanes on III−V semiconductor surfaces, we additionally performed X-ray photoelectron spectrometry (XPS). An XPS survey scan acquired on InAs surfaces before and after the grafting of 12,12,13,13,14,14,15,15,16,16,17,17 3b. The molecule's high content of Fluor serves as a marker in XPS.…”

“…The hydrolytic stability of InAs in neutral water was reported . However, GaSb is not stable in aqueous environment. ,, A water-free surface chemistry is thus required to prevent the oxidation of GaSb in water, which is much faster and more detrimental than the air oxidation. Trimethoxysilane derivatives are an interesting approach for monolayer formation on metal oxides, and we demonstrate in the following the successful surface modification by silane surface chemistry.…”

“…While initially limited to sufficient quantities of analyte molecules, the surface enhancement effect using plasmonic nanostructures and metamaterials helps to downscale the necessary quantity and has been successfully applied for the detection of monolayers of chemical moieties, − proteins, − lipid membranes, or dust particles . Different strategies have been employed to reduce the detection limit, such as optimizing the nanoantenna geometrically to achieve highest field enhancement at a target wavelength, ,,− creating an adapted tuning ratio between the antenna resonance and the molecular vibration, , exploiting nanoantenna systems with sharp Fano-like resonances or collective array resonances, , or using alternative plasmonic materials with a tunable dielectric function to cover various spectral ranges. ,− Comprehensive reviews have recently discussed these approaches for improving surface-enhanced infrared absorption (SEIRA) spectroscopy. , …”