Colorful InAs Nanowire Arrays: From Strong to Weak Absorption with Geometrical Tuning

Abstract

One-dimensional nanostructure arrays can show fascinatingly different, tunable optical response compared to bulk systems. Here we study theoretically and demonstrate experimentally how to engineer the reflection and absorption of light in epitaxially grown vertical arrays of InAs nanowires (NWs). A striking observation is optically visible colors of the array, which we show can be tuned depending on the geometrical parameters of the array. Specifically, larger diameter NW arrays absorb light more effectively out to a longer wavelength compared to smaller diameter arrays. Thus, controlling the diameter provides a way to tune the optically observable color of an array. We also find that arrays with a larger amount of InAs material reflect less light (or absorb more light) than arrays with less material. On the basis of these two trends, InAs NW arrays can be designed to absorb light either much more or much less efficiently than a thin film of an effective medium containing the same amount of InAs as the NW array. The tunable absorption and low area filling factor of the NW arrays compared to thin film bode well for III-V photovoltaics and photodetection.

Localized absorption in aluminum mask in visible spectrum due to longitudinal modes in vertical silicon nanowire arrays

“…One study showed that hemispherical gold nanoparticles on the top of InAs nanowires had a negligible effect on their reflectance spectra. 20 However, in another study, silver, copper, and gold masks on silicon nanowires decreased overall absorption across the solar spectrum. 21 Thus, the role that masks play in optical characteristics is not very clear.…”

Electrodeposition of InSb branched nanowires: Controlled growth with structurally tailored properties

“…Specifically, for example, size-quantization and dielectric confinement related to the size (e.g., diameter/length), shape (e.g., taper), and periodicity of the NWs have been engineered for applications in NW-based photovoltaics and photodetectors with considerable success. [21][22][23][24][25][26][27] The versatility of the structure arises from the fact that two fundamental length scales, namely, the extinction distance and the minority carrier diffusion length, can be effectively decoupled in a device with NW arrays. Tapered or stepped structures, including nano-needle nanowires (NNNW) and dualdiameter nanowires (DDNW) have shown enhanced light trapping and absorption, in comparison to nanowires with a uniform diameter along their length.…”

Diameter-Dependent Photocurrent in InAsSb Nanowire Infrared Photodetectors

“…25 To investigate this diameter dependence of the absorption in detail, electromagnetic modelling using a scattering matrix method 26,27 was performed. In the modelling, cylindrical wires of length L and with diameter d were placed in a square array with pitch p and embedded in a dielectric with a refractive index of n = 1.6 corresponding to the resist.…”