Long indium-rich InGaAs nanowires by SAG-HVPE.

We demonstrate the selective area growth of InGaAs nanowires (NWs) on GaAs (111)B substrates using hydride vapor phase epitaxy (HVPE). A high growth rate of more than 50m hand high aspect ratio NWs were obtained. Composition along the NWs was investigated by energy dispersive x-ray spectroscopy giving an average indium composition of 84%.

Detection of Be dopant pairing in VLS grown GaAs nanowires with twinning superlattices.

Control over the distribution of dopants in nanowires is essential for regulating their electronic properties, but perturbations in nanowire microstructure may affect doping. Conversely, dopants may be used to control nanowire microstructure including the generation of twinning superlattices (TSLs)-periodic arrays of twin planes. Here the spatial distribution of Be dopants in a GaAs nanowire with a TSL is investigated using atom probe tomography.

off-axis electron holography of real-time dopant diffusion in GaAs nanowires.

Off-axis electron holography was used to reveal remote doping in GaAs nanowires occurring duringannealing in a transmission electron microscope. Dynamic changes to the electrostatic potential caused by carbon dopant diffusion upon annealing were measured across GaAs nanowires with radial p-p+ core-shell junctions. Electrostatic potential profiles were extracted from holographic phase maps and built-in potentials () and depletion layer widths (DLWs) were estimated as function of temperature over 300-873 K.

Thermal Conductivity of GaAs Nanowire Arrays Measured by the 3ω Method.

Vertical nanowire (NW) arrays are the basis for a variety of nanoscale devices. Understanding heat transport in these devices is an important concern, especially for prospective thermoelectric applications. To facilitate thermal conductivity measurements on as-grown NW arrays, a common NW-composite device architecture was adapted for use with the 3ω method.

Thermal transport in twinning superlattice and mixed-phase GaAs nanowires.

With continuing advances in semiconductor nanowire (NW) growth technologies, synthesis of tailored crystal structures is gradually becoming a reality. Mixtures of the bulk zinc blende (ZB) and wurtzite (WZ) phase can be achieved in III-V NWs under various growth conditions. Among the possible crystal structures, the twinning superlattice (TSL) has attracted particular interest for tuning photonic and electronic properties.

Phase Diagram for Twinning Superlattice Te-Doped GaAs Nanowires.

Twinning superlattices (TSLs) are a growing class of semiconductor structures proposed as a means of phonon and optical engineering in nanowires (NWs). In this work, we examine TSL formation in Te-doped GaAs NWs grown by a self-assisted vapor-liquid-solid mechanism (with a Ga droplet as the seed particle), using selective-area molecular beam epitaxy. In these NWs, the TSL structure is comprised of alternating zincblende twins, whose formation is promoted by the introduction of Te dopants.

Conformal Growth of Radial InGaAs Quantum Wells in GaAs Nanowires.

GaAs-InGaAs-GaAs core-shell-shell nanowire (NW) structures were grown by gas source molecular beam epitaxy using the selective-area, self-assisted, vapor-liquid-solid method. The structural, morphological, and optical properties of the NWs were examined for different growth conditions of the InGaAs shell. With increasing In concentration of the InGaAs shell, the growth transitioned from preferential deposition at the NW base to the Stranski-Krastanov growth mode where InGaAs islands formed along the NW length.

Modelling thermoelectric transport in III-V nanowires using a Boltzmann transport approach: a review.

A review of models for determining the thermoelectric transport coefficients [Formula: see text] (Seebeck coefficient), [Formula: see text] (electrical conductivity), and [Formula: see text] (electronic thermal conductivity) is presented, for the cases of bulk and nanowire structures, along with derivations and a discussion of calculation methods. Results for the transport coefficients in GaAs, InAs, InP and InSb are used to determine the thermoelectric figure of merit, where an enhancement by two orders of magnitude is found for the nanowire case as compared with the bulk. The optimal electron concentration is determined as a function of nanowire diameter for both background and modulation doped nanowires.

Formation Mechanism of Twinning Superlattices in Doped GaAs Nanowires.

Recent investigations of III-V semiconductor nanowires have revealed periodic zinc-blende twins, known as twinning superlattices, that are often induced by a high-impurity dopant concentration. In the present study, the relationship between the nanowire morphology, crystal structure, and impurity dopant concentration (Te and Be) of twinning superlattices has been studied in GaAs nanowires grown by molecular beam epitaxy using the self-assisted (with a Ga droplet) vapor-liquid-solid process. The contact angle between the Ga droplet and the nanowire top facet decreased linearly with the dopant concentration, whereas the period of the twinning superlattices increased with the doping concentration and was proportional to the nanowire radius.

Si Doping of Vapor-Liquid-Solid GaAs Nanowires: n-Type or p-Type?

The incorporation of Si into vapor-liquid-solid GaAs nanowires often leads to p-type doping, whereas it is routinely used as an n-dopant of planar layers. This property limits the applications of GaAs nanowires in electronic and optoelectronic devices. The strong amphoteric behavior of Si in nanowires is not yet fully understood.

Efficient wave optics modeling of nanowire solar cells using rigorous coupled-wave analysis.

We investigate the accuracy of rigorous coupled-wave analysis (RCWA) for near-field computations within cylindrical GaAs nanowire solar cells and discover excellent accuracy with low computational cost at long incident wavelengths but poor accuracy at short incident wavelengths. These near fields give the carrier generation rate, and their accurate determination is essential for device modeling. We implement two techniques for increasing the accuracy of the near fields generated by RCWA and give some guidance on parameters required for convergence along with an estimate of their associated computation times.

GaP nanowire betavoltaic device.

A betavoltaic device is reported that directly converts beta energy from a Ni radioisotope into electrical energy by impact ionization in a GaP nanowire array. The GaP nanowires are grown in a periodic array by molecular beam epitaxy on silicon using the self-assisted vapor-liquid-solid method. By growing GaP nanowires with large packing fraction and length on the order of the maximum beta range, the nanowires can efficiently capture the betas with high energy conversion efficiency while using inexpensive Si substrates.

Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes.

The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies [Formula: see text] are observed. The electronic phase coherence length at low temperatures exceeds the channel length.

Resonant photo-thermal modification of vertical gallium arsenide nanowires studied using Raman spectroscopy.

Gallium arsenide nanowires have shown considerable promise for use in applications in which the absorption of light is required. When the nanowires are oriented vertically, a considerable amount of light can be absorbed, leading to significant heating effects. Thus, it is important to understand the threshold power densities that vertical GaAs nanowires can support, and how the nanowire morphology is altered under these conditions.

Model of patterned self-assisted nanowire growth.

Vertically oriented and ordered GaAs nanowire arrays have been grown by the self-assisted mechanism using substrates prepared with nano-patterned oxide templates. Patterned Ga-assisted GaAs nanowire growth on (111) silicon by molecular beam epitaxy showed that the axial and radial growth rates increased with increasing interhole spacing. A model is described which accounts for the correlation of the final length and diameter with pattern pitch.

Enhanced photothermal conversion in vertically oriented gallium arsenide nanowire arrays.

The photothermal properties of vertically etched gallium arsenide nanowire arrays are examined using Raman spectroscopy. The nanowires are arranged in square lattices with a constant pitch of 400 nm and diameters ranging from 50 to 155 nm. The arrays were illuminated using a 532 nm laser with an incident energy density of 10 W/mm(2).

Highly ordered vertical GaAs nanowire arrays with dry etching and their optical properties.

We report fabrication methods, including metal masks and dry etching, and demonstrate highly ordered vertical gallium arsenide nanowire arrays. The etching process created high aspect ratio, vertical nanowires with insignificant undercutting from the mask, allowing us to vary the diameter from 30 nm to 400 nm with a pitch from 250 nm to 1100 nm and length up to 2.2 μm.

Temperature-dependent electron mobility in InAs nanowires.

Effective electron mobilities are obtained by transport measurements on InAs nanowire field-effect transistors at temperatures ranging from 10 to 200 K. The mobility increases with temperatures below ∼30-50 K, and then decreases with temperatures above 50 K, consistent with other reports. The magnitude and temperature dependence of the observed mobility can be explained by Coulomb scattering from ionized surface states at typical densities.

A growth interruption technique for stacking fault-free nanowire superlattices.

An experimental approach to achieving phase purity in nanowires through molecular beam epitaxy growth is presented. Superlattice heterostructured nanowires were grown, consisting of alternating layers of GaAsP and GaP. The observed core-multishell heterostructure, extending axially and radially, is attributed to simultaneous Au-assisted vertical growth and diffusion-limited radial growth along lateral nanowire facets.

GaAs core--shell nanowires for photovoltaic applications.

We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices.

Growth and characterization of GaAs nanowires on carbon nanotube composite films: toward flexible nanodevices.

Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films.

Multiple quantum well AlGaAs nanowires.

This letter reports on the growth, structure, and luminescent properties of individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy performed on individual NWs are consistent with a configuration composed of conical segments stacked along the NW axis.