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Nanowires have promising applications as photodetectors with superior ability to tune absorption with morphology. Despite their high optical absorption, the quantum efficiencies of these nanowire photodetectors remain low due to difficulties in fabricating a shallow junction using traditional doping methods. As an alternative, we report nonconventional radial heterojunction photodiodes obtained by conformal coating of an indium oxide layer on silicon nanowire arrays. The indium oxide layer has a high work function which induces a strong inversion in the silicon nanowire and creates a virtual p-n junction. The resulting nanowire photodetectors show efficient carrier separation and collection, leading to an improvement of quantum efficiency up to 0.2. In addition, by controlling the nanowire radii, the spectral responses of the In2O3/Si nanowire photodetectors are tuned over several visible light wavelengths, creating a multispectral detector. Our approach is promising for the development of highly efficient wavelength-selective photodetectors.

The responsivity spectrum of a photodetector is one of its key specifications. It ultimately originates from the combination of the absorption spectrum of the photosensitive region and the internal quantum efficiency. Many applications of photodetectors would benefit from an improved ability to tailor the responsivity spectrum. This is particularly true for color and multispectral imaging. The absorption spectrum of a bulk (unstructured) semiconductor is fixed however, being determined by its complex refractive index. Here, we review recent work that demonstrates that the absorption spectrum of a photodetector can be controlled via waveguide resonances in semiconductor nanowires. We discuss the physical interpretation for this phenomenon. We review work in which p-i-n photodiodes were incorporated into vertically oriented silicon nanowires, and then used for color imaging. We review work in which tandem-style photodetectors were demonstrated, with a p-i-n silicon nanowire photodiode formed above an n-i-p planar silicon photodiode. We review work in which narrowband photodetection across the visible-to-infrared was demonstrated using germanium nanowires. Finally, we describe related work in which silicon nanowires have been explored for other applications, namely solar cells.

At visible wavelengths, photodetection in three channels (red, green and blue) enables color imaging. Yet the spectra of most materials provide richer information than just color, and therefore considerable interest exists for imaging with multiple spectral bands across the visible to infrared. This endeavor requires narrowband photodetection, which is generally achieved by combining broadband photodetectors with filters or spectrometers, but with added bulk and cost. Here we report, for the first time to our knowledge, vertical germanium nanowires as narrowband photodetectors. Our devices exhibit spectral response peaks that are as narrow as 40 nm and can be shifted from visible (~600 nm) to infrared (~1600 nm) wavelengths by appropriate design. The spectral selectivity arises from the nanowires acting as waveguides and, surprisingly, is enhanced by radial narrowing of the carrier collection region due to surface recombination. The incorporation of germanium into integrated circuits in a high yield and c...

We created a polymer-embedded TiO2 nanodiscs device with a robust tunable color filters that preserve veiy sharp spectral bands through spatial variations of the pitch of the meta array.

We demonstrated through a series of electromagnetic simulations and FTIR measurements a proof of concept for using vertically aligned arrays of InSb nanostructures as devices for selective SWIR and MWIR light absorption.

This chapter provides an overview of fabrication of silicon nanowires by top-down etching methods. The focus will be on wet and dry etching methods to achieve vertically aligned silicon nanowires. We will start by building an understanding of the dry etching process. Then we will delve deeper into the mechanisms, benefits, and drawbacks of these dry etching processes. This is followed by wet etching methods, primarily metal-assisted chemical etching methods. Finally, we will provide a guideline to fabricate vertically aligned Si nanowire arrays with both dry and wet chemical processes.

We present experimental results demonstrating multiple order Smith-Purcell radiation in high aspect ratio Silicon Nanowires structures using low-energy electrons (2.5–10keV). These produce emission spanning the visible, paving the way to a fully tunable ultraviolet source.

International audience; A single silicon nanowire core-shell structure has been elaborated. Technological stages of the process are presented. The device results in a P-i-N radial junction: the core is a P-type silicon nanowire encapsulated in an intrinsic thin silicon layer and an N-type doped silicon layer. Scanning electron microscopy observations, as well as the electrical I(V) characterisation on single nanowires, are presented.

International audience; The efficient photon management in nanowires coupled with tunable absorption can provide a significant advancement in the current solar cell technology. Adding a shell on the nanowire (NW) offers an extra degree of freedom for tailoring the NW absorption. Calculations are performed to study the shell-induced changes in the core absorption of an ideal Si nano-cylinder after enclosing it with conformal dielectrics of different thicknesses and permittivities. The calculation shows that coating the Si nanowires with nonabsorbing or weakly absorbing dielectric shells can significantly improve the mean spectral absorption efficiency of the Si core for optimized thickness and extinction. Experimental data are brought from a neighboring system consisting of individual NW junctions sandwiched between an oxidized planar Si substrate and a top-deposited oxide layer. The measured absorption spectra show a good agreement with the theoretical spectra, with a mean spectral absorption enhancement after oxide coating as high as 5.7 in axial junctions, exceeding its theoretical counterpart that is limited to similar to 1.5. Coating the nanowires with an optimized oxide shell provides a new approach to significantly enhance the light harvesting in nanowires and will lead to more efficient photovoltaics.

International audience; The introduction of Hydrogen Chloride during the in-situ doping of Silicon Nanowires (SiNWs) grown using the Vapour Liquid Solid (VLS) mechanism was investigated. Compared with non-chlorinated atmospheres, the use of HCl with dopant gases considerably improves the surface morphology of the SiNWs, leading to extremely smooth surfaces and a greatly reduced tapering. The variations in the wire diameter are massively reduced for boron doping, and can not be measured at 600°C for phosphorous over several tens of micrometers. This remarkable feature is accompanied by a frozen gold migration from the catalyst, with no noticeable levels of gold clusters observed using scanning electron microscopy. A detailed study of the NWs apparent resistivity reveals that the dopant incorporation is effective for both types of doping. A graph linking the apparent resistivity to the dopant to silane dilution ratio is built for both types of doping and discussed in the frame of the previous results.

Summary The growing research in the field of photovoltaics has led to various strategies for increasing the light interaction in absorbers, for instance the use of nanostructures like nanowires where leaky mode resonances enhanced absorption efficiency. Towards this goal, we present a study of the light absorption in single Si nanowires, by means of microphotocurrent spectroscopy combined with transport measurements of carrier diffusion length using the electron beam induced current technique. The study is performed on different diameter nanowires with Schottky junctions created by doping modulation during Chemical Vapor Deposition–Vapor Liquid Solid growth. We show that the photocurrent spectra of single Si nanowires do not follow monotonous profiles as bulk silicon, but rather have steep valleys and peaks whose position and intensity are diameter dependent. These sharp modulations result from a resonant coupling between incident photons and cavity modes of the nanowires. A good agreement between the experiment and the theoretical fit using Mie theory is observed with a red shift in the

Undoped silicon nanowire (Si NW) field-effect transistors (FETs) with a back-gate configuration have been fabricated and characterized. A thick (200 nm) Si3N4 layer was used as a gate insulator and a p++ silicon substrate as a back gate. Si NWs have been grown by the chemical vapour deposition method using the vapour–liquid–solid mechanism and gold as a catalyst. Metallic contacts have been deposited using Ni/Al (80 nm/120 nm) and characterized before and after an optimized annealing step at 400 °C, which resulted in a great decrease in the contact resistance due to the newly formed nickel silicide/Si interface at source and drain. These optimized devices show a good hole mobility of around 200 cm2 V−1 s−1, in the same range as the bulk material, with a good ON current density of about 28 kA cm−2. Finally, hysteretic behaviour of NW channel conductance is discussed to explain the importance of NW surface passivation.

Silicon nanowires (Si NWs) are promising candidates for field-effect transistor (FET) conduction channel. Planar configuration using a back gate is an easy way to study these devices. We demonstrate the possibility to build high performance FET using a simple silicidation process leading to high effective holes' mobility between 130 cm2⋅V-1⋅s-1 and 200 cm2⋅V-1⋅s-1 and good ION/IOFF ratio up to 105. Moreover we investigated the possibility to passivate the NWs using either a high-k dielectric layer or a thermal oxide shell around the NWs. This leads to a reduction of the hysteretic behavior during the gate voltage sweep from 30 V to 1 V depending on the material and the gate configuration.

We demonstrate photodetectors for visible-to-infrared imaging, comprising vertical germanium nanowires on a silicon substrate, with a suspended graphene layer as the top electrical contact. Measured responsivity spectra show peaks that shift with increasing nanowire diameter.