Mid-IR plasmonic compound with gallium oxide toplayer formed by GaSb oxidation in water

The oxidation of GaSb in aqueous environments has gained interest by the advent of plasmonic antimonide-based compound semiconductors for molecular sensing applications. This work focuses on quantifying the GaSb–water reaction kinetics by studying a model compound system consisting of a 50 nm thick GaSb layer on a 1000 nm thick highly Si-doped epitaxial grown InAsSb layer. Tracing of phonon modes by Raman spectroscopy over 14 h of reaction time shows that within 4 h, the 50 nm of GaSb, opaque for visible light, transforms to a transparent material. Energy-dispersive x-ray spectroscopy shows that the reaction leads to antimony depletion and oxygen incorporation. The final product is a gallium oxide. The good conductivity of the highly Si-doped InAsSb and the absence of conduction states through the oxide are demonstrated by tunneling atomic force microscopy. Measuring the reflectivity of the compound layer structure from 0.3 to 20 μm and fitting of the data by the transfer-matrix method allows us to determine a refractive index value of 1.6 ± 0.1 for the gallium oxide formed in water. The investigated model system demonstrates that corrosion, i.e. antimony depletion and oxygen incorporation, transforms the narrow band gap material GaSb into a gallium oxide transparent in the range from 0.3 to 20 μm