Vertically Aligned Arrays of InSb Nanostructures for Tuning Light Absorption in the Mid-Infrared

Abstract

Infrared detection is valuable across a diverse range of fields. Military applications have long been the focus of development of infrared detection technology, but as accessibility to infrared detectors grows, industries ranging from waste management to medicine have shown broad uses for the technology. Imaging of biological samples is particularly well suited for near and mid infrared imaging as opaque superficial layers often inhibit the use of visible light to detect underlying structures which may hold diagnostic value. Infrared detecting devices are typically underutilized in a biomedical setting despite there being many potential applications. The primary objective of this research was to provide a proof of concept for a novel transmission filters system in the near and mid infrared range using vertically oriented indium antimonide (InSb) nanostructures. This was achieved by conducting optical simulations of InSb nanowires, developing an ICP-RIE etching process suitable for InSb, and, lastly, by measuring specular reflectance of the InSb nanostructure arrays using FT-IR microscopy. Optical simulations showed that nanowire diameter will shift spectral response, suggesting that InSb would make a suitable selective filter which can be tuned with geometry. Etching InSb nanostructures with a CH4/H2/Ar based ICP-RIE process was shown to minimize re-deposition and tapering, but not to eliminate either. Preliminary data showed that an addition of HBr to the CH4/H2/Ar process could potentially mitigate both issues. Finally, an FT-IR microscope was used to measure specular reflectance, and confirmed that spectral response can be tuned with InSb nanowire dimensions in a 2 µm to 7 µm wavelength range. This confirms that InSb nanowire arrays are a candidate for wavelength specific absorbers which may be able to be used as passive transmission filters or even be developed as active detectors in the future.