Nanowire-based Devices Research Articles

A comprehensive review of template-synthesized multi-component nanowires: From interfacial design to sensing and actuation applications

Nanowires are one of the most promising nano-building blocks for many applications, including sensors/biosensors, electronics, photonics, energy conversion and storage devices, MEMS and NEMS, biotechnology and nanomedicine. With the growing demands of multi-purpose and multi-functional materials in these fields, different types of multi-component nanowires with complex structures have been designed and fabricated. Among various fabrication methods, porous anodic aluminum oxide (AAO) and polycarbonate (PC) membranes are well-established hard templates that have been used for synthesizing a variety of nanowires and nanowire structures. In this article, a comprehensive review of template-synthesized multi-component nanowire structures has been given, including multi-segmented, core-shell and multi-element nanowires, which can be synthesized by using these hard templates in a sequential or parallel way. Besides, the assembly and integration of different functions and properties into smaller and lighter devices require careful interfacial design and synthesis of multi-component nanowires. The interfacial structure and properties, such as interface uniformity, intermetallic compound formation and surface oxidation, have significant impact on the electrical and thermal conductivity, mechanical strength, functionality, stability and reliability of nanowire-based electronics and devices. A rational interfacial design is crucially important to improve these properties of nanowire devices for emerging multi-functional sensors and actuators, due in fact that sensors and actuators are among the most important components in many electronics and products. Multi-component nanowire based sensors and actuators have potential applications in a wide range of mechanical, electrical, thermal, and biomedical devices.

Back-Gate GaN Nanowire-Based FET Device for Enhancing Gas Selectivity at Room Temperature.

In this work, a TiO2-coated GaN nanowire-based back-gate field-effect transistor (FET) device was designed and implemented to address the well-known cross-sensitive nature of metal oxides. Even though a two-terminal TiO2/GaN chemiresistor is highly sensitive to NO2, it suffers from lack of selectivity toward NO2 and SO2. Here, a Si back gate with C-AlGaN as the gate dielectric was demonstrated as a tunable parameter, which enhances discrimination of these cross-sensitive gases at room temperature (20 °C). Compared to no bias, a back-gate bias resulted in a significant 60% increase in NO2 response, whereas the increase was an insignificant 10% in SO2 response. The differential change in gas response was explained with the help of a band diagram, derived from the energetics of molecular models based on density functional theory (DFT). The device geometries in this work are not optimized and are intended only for proving the concept.

Nanowire Waveguides and Lasers: Advances and Opportunities in Photonic Circuits.

Due to their single-crystalline structures, comparatively large aspect ratios, tight optical confinement and smooth surfaces, nanowires have increasingly attracted research interests for both fundamental studies and technological applications in on-chip photonic devices. This class of nanostructures typically have cross-sections of 2~200 nm and lengths upwards of several micrometers, allowing for the bridging of the nanoscopic and macroscopic world. In particular, the lasing behaviors can be established from a nanowire resonator with positive feedback via end-facet reflection, making the nanowire a promising candidate in the next generation of optoelectronics. Consequently, versatile nanowire-based devices ranging from nanoscale coherent lasers, optical sensors, waveguides, optical switching, and photonic networks have been proposed and experimentally demonstrated in the past decade. In this article, significant progresses in the nanowire fabrication, lasers, circuits, and devices are reviewed. First, we focus on the achievements of nanowire synthesis and introduce the basics of nanowire optics. Following the cavity configurations and mode categories, then the different light sources consisting of nanowires are presented. Next, we review the recent progress and current status of functional nanowire devices. Finally, we offer our perspective of nanowires regarding their challenges and future opportunities in photonic circuits.

Design of a Horizontally Aligned Perovskite Nanowire LED With Improved Light Extraction

Within a short span of a few years, metal halide perovskite light-emitting diodes have shot past the 20 percent external quantum efficiency mark. As the material quality and photoluminescent quantum yield of perovskite are already at par with the state-of-the-art, light extraction for further quantum efficiency enhancement has taken the center stage of scientific interest. Herein, we demonstrate horizontally aligned perovskite nanowire-based light-emitting diodes with 50.9 percent of light extraction efficiency, with a 2.9-fold increase compared to the planar counterpart. The absorption spectra of the plane wave incidence exhibit the weak trapping of light within the emission range. Purcell factors of horizontal perovskite nanowires with different diameters are also studied, which provides design guidelines for applying the horizontally aligned perovskite nanowires for multifarious optoelectronic applications such as lasing. The resonance peak positioned at 530 nm wavelength shows the nanowire antennas’ effect in the nanowires with diameters of 300 nm, 500 nm, and 550 nm respectively. Furthermore, the fabrication process of the light-emitting devices based on ink-jet printing has also been proposed. This report not only provides an in-depth understanding of light extraction in nanowire LEDs but also heralds the inception of horizontally aligned perovskite nanowire-based optoelectronic devices.

Technique for Fabricating Ferromagnetic/Silicon Active Devices and Their Transport Properties

Semiconductor nanowires are unique materials for studying nanoscale phenomena; the possibility of forming silicon nanowires on bulk silicon-on-insulator substrates in a top-down process ensures complete incorporation of this technology into integrated electronic systems. In addition, the use of ferromagnetic contacts in combination with the high quality of ferromagnetic–semiconductor interfaces open up prospects for the use of such structures in spintronics devices, in particular, spin transistors. A simple approach is proposed to create semiconductor nanowire-based active devices, specifically, bottom-gate Schottky-barrier field-effect transistors with a metal (Fe) source and drain synthesized on a silicon-on-insulator substrate and the transport characteristics of the designed transistors are investigated.

Electrodeposited nickel nanowires for magnetic-field effect transistor (MagFET)

The growing interest in magnetic nanowires (NWs) is connected to possibility of employing them for advanced applications in wide technological fields, such as data storage and biotechnology. In addition, NWs can be used as sensor devices for several applications, since they present high sensitivity to their environment. One of the major challenges when dealing with transport measurements in NWs is to trap them between electrodes, which allows electrical characterization and therefore fabrication of nanowire-based devices. Electrically neutral NWs can be deposited by dielectrophoresis (DEP) method, which requires the application of an alternating electric field between electrodes. In this work, Ni nanowires (NiNWs) fabricated by electrodeposition technique and properly dispersed in a dimethylformalmide (DMF) solution were deposited on top of Pt electrodes using the DEP method. The deposited NiNWs exhibit initially a Schottky-like current versus voltage behavior due to the high contact resistance between NiNW and electrode. Its reduction down to three orders of magnitude, reaching value less than the NiNW resistance, was achieved by depositing an ion beam-assisted 10 nm-thick Pt layer over the NWs extremities. Therefore, this method presents a suitable process of NWs deposition and electrical characterization. This can be used for investigation of electrical transport properties of individual NWs and fabrication of NWsbased devices, such as sensors and field-effect transistors. Especially for ferromagnetic NWs, one can use the present method for fabrication of magnetic field-effect transistors (MagFET).

Studies on Carrier Recombination in GaN/AlN Quantum Dots in Nanowires with a Core-Shell Structure.

GaN quantum dots embedded in nanowires have attracted much attention due to their superior optical properties. However, due to the large surface-to-volume ratio of the nanowire, the impacts of surface states are the primary issue responsible for the degradation of internal quantum efficiency (IQE) in heterostructured dot-in-nanowires. In this paper, we investigate the carrier recombination mechanism of GaN/AlN dot-in-nanowires with an in situ grown AlN shell structure. Ultraviolet photoelectron spectroscopy (UPS) measurements were performed to describe the band bending effect on samples with different shell thicknesses. Temperature-dependent photoluminescence (TDPL) data support that increasing the AlN shell thickness is an efficient way to improve internal quantum efficiency. Detailed carrier dynamics was analyzed and combined with time-resolved photoluminescence (TRPL). The experimental data are consistent with our physical model that the AlN shell can effectively flatten the band bending near the surface and isolate the surface non-radiative recombination center. Our systematic research on GaN/AlN quantum dots in nanowires with a core–shell structure may significantly advance the development of a broad range of nanowire-based optoelectronic devices.

Semiconductivity Transition in Silicon Nanowires by Hole Transport Layer.

The surface of nanowires is a source of interest mainly for electrical prospects. Thus, different surface chemical treatments were carried out to develop recipes to control the surface effect. In this work, we succeed in shifting and tuning the semiconductivity of a Si nanowire-based device from n- to p-type. This was accomplished by generating a hole transport layer at the surface by using an electrochemical reaction-based nonequilibrium position to enhance the impact of the surface charge transfer. This was completed by applying different annealing pulses at low temperature (below 400 °C) to reserve the hydrogen bonds at the surface. After each annealing pulse, the surface was characterized by XPS, Kelvin probe measurements, and conductivity measured by FET based on a single Si NW. The mechanism and conclusion were supported experimentally and theoretically. To this end, this strategy has been demonstrated as an essential tool which could pave a new road for regulating semiconductivity and for other low-dimensional nanomaterials.

Hot electrons in a nanowire hard X-ray detector

Nanowire chip-based electrical and optical devices such as biochemical sensors, physical detectors, or light emitters combine outstanding functionality with a small footprint, reducing expensive material and energy consumption. The core functionality of many nanowire-based devices is embedded in their p-n junctions. To fully unleash their potential, such nanowire-based devices require – besides a high performance – stability and reliability. Here, we report on an axial p-n junction GaAs nanowire X-ray detector that enables ultra-high spatial resolution (~200 nm) compared to micron scale conventional ones. In-operando X-ray analytical techniques based on a focused synchrotron X-ray nanobeam allow probing the internal electrical field and observing hot electron effects at the nanoscale. Finally, we study device stability and find a selective hot electron induced oxidization in the n-doped segment of the p-n junction. Our findings demonstrate capabilities and limitations of p-n junction nanowires, providing insight for further improvement and eventual integration into on-chip devices.

Temperature induced shifts of Yu\u2013Shiba\u2013Rusinov resonances in nanowire-based hybrid quantum dots

The strong coupling of a superconductor to a spinful quantum dot results in Yu–Shiba–Rusinov discrete subgap excitations. In isolation and at zero temperature, the excitations are sharp resonances. In transport experiments, however, they show as broad differential conductance peaks. Here we obtain the lineshape of the peaks and their temperature dependence in superconductor–quantum dot–metal nanowire-based devices. Unexpectedly, we find that the peaks shift in energy with temperature, with the shift magnitude and sign depending on ground state parity and bias voltage. Additionally, we empirically find a power-law trend of the peak area versus temperature. These observations are not explained by current models.

ZnO Nanowire-Based Field Emission Devices Through a Microelectronic Compatible Route

Nanostructured zinc oxide (ZnO) has attracted considerable interest for a wide range of applications, including its use as an active layer in gas sensor devices and as promising emitters for field emission devices. Although it is interesting for FE purposes, the synthesis of this material can be complex and non-compatible with microelectronic processes. To overcome this issue, this paper explores ZnO nanowires growth through thermal oxidation of zinc thin films. We applied this IC-compatible procedure to fabricate field emission cathodes. Analyses of Raman spectroscopy, X‑ray photoelectron spectrometry, X‑ray diffractometry and scanning electron microscopy confirmed that the processes applied were well succeeded in obtaining nanoscale structures of ZnO with dimensions up to 4 micrometers in length and 30‑100 nanometers in diameter. Electrical characterization showed an intense electron field emission on the active area of the device, with a low turn-on electric field (2.4 volts/micrometer). An innovative system based on image processing allowed electrical current mapping throughout the active area of the devices, providing information about the uniformity of the emitted current. These results demonstrate that the low-complex fabrication procedures adopted as well as the ZnO nanomaterial itself are suitable for FE devices development.

Direct Growth of Light-Emitting III-V Nanowires on Flexible Plastic Substrates.

Semiconductor nanowires are routinely grown on high-priced crystalline substrates as it is extremely challenging to grow directly on plastics and flexible substrates due to high-temperature requirements and substrate preparation. At the same time, plastic substrates can offer many advantages such as extremely low price, light weight, mechanical flexibility, shock and thermal resistance, and biocompatibility. We explore the direct growth of high-quality III–V nanowires on flexible plastic substrates by metal-organic vapor phase epitaxy (MOVPE). We synthesize InAs and InP nanowires on polyimide and show that the fabricated NWs are optically active with strong light emission in the mid-infrared range. We create a monolithic flexible nanowire-based p–n junction device on plastic in just two fabrication steps. Overall, we demonstrate that III–V nanowires can be synthesized directly on flexible plastic substrates inside a MOVPE reactor, and we believe that our results will further advance the development of the nanowire-based flexible electronic devices.

Non-Hermitian topological phases in an extended Kitaev model

In this work we address the study of topological phase protection of open quantum systems. Using the self-energy formalism, we investigate the paradigmatic case of an extended Kitaev model. The results show how the topological order can be affected by coupling the system to two external leads, giving rise to Non-Hermitian topological phases. Our results could be useful in spectroscopic measurements made on nanowire-based mesoscopic devices.

Electrical probing of carrier separation in InAs/InP/GaAsSb core-dualshell nanowires

We investigate the tunnel coupling between the outer p-type GaAsSb shell and the n-type InAs core in catalyst-free InAs/InP/GaAsSb core-dualshell nanowires. We present a device fabrication protocol based on wet-etching processes on selected areas of the nanostructures that enables multiple configurations of measurements in the same nanowire-based device (i.e. shell-shell, core-core and core-shell). Low-temperature (4.2 K) transport in the shell-shell configuration in nanowires with 5 nm-thick InP barrier reveals a weak negative differential resistance. Differently, when the InP barrier thickness is increased to 10 nm, this negative differential resistance is fully quenched. The electrical resistance between the InAs core and the GaAsSb shell, measured in core-shell configuration, is significantly higher with respect to the resistance of the InAs core and of the GaAsSb shell. The field effect, applied via a back-gate, has an opposite impact on the electrical transport in the core and in the shell portions. Our results show that electron and hole free carriers populate the InAs and GaAsSb regions respectively and indicate InAs/InP/GaAsSb core-dualshell nanowires as an ideal system for the investigation of the physics of interacting electrons and holes at the nanoscale.

Highly uniform InGaAs/InP quantum well nanowire array-based light emitting diodes

III-V semiconductor nanowire infrared light emitting diodes (LEDs) have great potential for the development of Si-based integrated photonics. In this paper, we report the growth of highly uniform triangular prism InGaAs/InP single quantum well (QW) nanowires using a 2-step growth by metal organic chemical vapour deposition by selective area epitaxy technique. Based on these nanowire arrays, we demonstrate nanowire array LEDs with strong electroluminescence at two main peaks, originating from the axial and radial QW respectively and control the relative emission of those two peaks. We further reveal that a long lateral contact of the nanowire LED results in more intense radial QW emission by shortening the current path to the radial quantum well. Our study provides an important foundation for the development of high-performance array nanowire-based devices such as high-power multi-wavelength LEDs, high power electrically switchable wavelength-selectors and QW infrared photodetectors.

Foreign-catalyst-free GaSb nanowires directly grown on cleaved Si substrates by molecular-beam epitaxy

We have successfully fabricated foreign-catalyst-free GaSb nanowires directly on cleaved Si (111) substrates by molecular-beam epitaxy. We find that GaSb nanowires with the absence and presence of Ga droplets at the tip can be simultaneously obtained on cleaved Si substrates without Ga pre-deposition. Systematic morphological and structural studies verify that the two kinds of nanowires presented have different growth mechanisms, which are vapor-solid and vapor-liquid-solid mechanisms. The growth of GaSb nanowires can also be achieved on cleaved Si (110) and Si (100) substrates. The cleavage plane of the Si substrate has an obvious influence on the growth of the GaSb nanowires. The growth direction and crystal quality of catalyst-free nanowires are independent of the cleavage plane of the substrate. Our results may facilitate the understanding of the growth mechanism of III–V nanowires and the integration of foreign-catalyst-free GaSb nanowire-based devices with mature semiconductor technology.

Surface traps-related nonvolatile resistive switching memory effect in a single SnO2:Sm nanowire

For nanostructure SnO2, it is very difficult for its electric properties to accurately control due to the presence of abundant surface states. The introduction of Sm can improve the traps in surface space charge region of SnO2 nanowires, resulting in a controllable storage charge effect. For the single nanowire-based two-terminal device, two surface state-related back-to-back diodes are formed. At a relatively large voltage, electrons can be injected into the traps in surface space charge region from negative electrode, resulting in a decrease of surface barrier connected with negative electrode, and contrarily electrons can be extracted from the traps in surface space charge region into positive electrode, resulting in an increase of surface barrier connected with positive electrode. The reversible injection and extraction induce a nonvolatile resistive switching memory effect.

Bottom-up device fabrication via the seeded growth of polymer-based nanowires.

The bottom-up assembly of nanoelectronic devices from molecular building blocks is a target of widespread interest. Herein we demonstrate an in situ seeded growth approach to produce a nanowire-based electrical device. This exploits the chemisorption of block terpolymer-based seed fibres with a thiophene-functionalised corona onto metal electrodes as the initial step. We then use these surface-bound seeds to initiate the growth of well-defined one-dimensional fibre-like micelles via the seeded growth method known as "Living crystallisation-driven self-assembly'' and demonstrate that they are capable of spanning an interelectrode gap. Finally, a chemical oxidation step was used to transform the nanofibres into nanowires to generate a two-terminal device. This seeded growth approach of growing well-defined circuit elements provides a useful new design tool for bottom-up device fabrication.

Microfluidic solution-processed organic and perovskite nanowires fabricated for field-effect transistors and photodetectors

A microfluidic template method of fabricating nanowires with solution-processable semiconductors is demonstrated, which can be utilized for constructing nanowire-based devices.

Wafer-scale fabrication and modification of silicon nano-pillar arrays for nanoelectronics, nanofluidics and beyond

We report on the fabrication and modification of a top-down nanofabrication platform for enormous parallel silicon nanowire-based devices. We explain the nanowire formation in detail, using an additive hybrid lithography step, optimising a reactive ion etching recipe for obtaining smooth and vertical nanowires under a hybrid mask, and embedding the nanowire in a dielectric membrane. The nanowires are used as a sacrificial template, removal of the nanowires forms arrays of well-defined nano-pores with a high surface density. This platform is expected to find applications in many different physical domains, including nanofluidics, (3D) nanoelectronics, as well as nanophotonics. We demonstrate the employment of the platform as field emitter arrays, as well as a state-of-the-art electro-osmotic pump.