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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. Using transmission electron microscopy, we investigated the crystal structure of NWs across various growth conditions (V/III flux ratio, temperature), finding periodic TSLs only at the low V/III flux ratio of 0.5 and intermediate growth temperatures of 492 to 537 °C. These results are explained by a kinetic growth model based on the diffusion flux feeding the Ga droplet.

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. This trend is explained within a nucleation model where there is a critical In flux below which the conformal growth is suppressed and the shell forms only at the NW base. Low growth temperature produced a more uniform In distribution along the NW length but resulted in quenching of the photoluminescence (PL) emission. Alternatively, reducing the shell thickness and increasing the V/III flux ratio resulted in conformal InGaAs shell growth and quantum dot-like PL emission. Our results indicate a pathway toward the conditions for conformal InGaAs shell growth required for satisfactory optoelectronic performance.

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. Our model, which is based entirely on surface energetics, is able to explain a unified formation mechanism of twinning superlattices in doped semiconductor nanowires.

Hybrid organic–inorganic halide perovskites have emerged as a disruptive technology in a number of fields, and recently, there has been increased interest in developing nanostructured perovskite materials, due to their extremely high photoluminescence quantum yields, optical absorption, and tolerance for defects. In this study, we report on the development of a facile room temperature synthesis method for high density monodispersed metal–organic halide perovskite nanoparticles using a diblock copolymer reverse micelle deposition (RMD) method. Compared to traditional ligated methods, we show that diblock copolymer micelle templating allows greater control over the size distribution due to controlled nucleation and crystal growth. By separating the precursor solvation and reaction steps through micelle templating, we show that micelle templating is a universal, atmospheric approach to producing a variety of perovskite nanoparticles, including methylammonium lead iodide (MAPbI3), methylammonium lead bromide ...

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). Nanowire temperatures were highly dependent on the nanowire diameter and were determined by measuring the spectral red-shift for both TO and LO phonons. The highest temperatures were observed for 95 nm diameter nanowires, whose top facets and sidewalls heated up to 600 and 440 K, respectively, and decreased significantly for the smaller or larger diameters studied. The diameter-dependent heating is explained by resonant coupling of the incident laser light into optical modes of the nanowires, resulting in increased absorption. Photothermal activity in a given nanowire diameter can be optimized by proper wavelength selection, as confirmed using computer simulations. This demonstrates that the photothermal properties of GaAs nanowires can be enhanced and tuned by using a photonic lattice structure and that smaller nanowire diameters are not necessarily better to achieve efficient photothermal conversion. The diameter and wavelength dependence of the optical coupling could allow for localized temperature gradients by creating arrays which consist of different diameters.

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. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

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. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter between 20 to 200 nm, with heights up to 2.5 microm. Transmission electron microscopy analysis of the NW-SWNT interface indicated that NW growth was initiated upon the surface of the nanotube composite films. Photoluminescence characterization of a single NW specimen showed high optical quality. Rectifying asymmetric current-voltage behavior was observed from contacted NW ensembles and attributed to the core-shell pn-junction within the NWs. Potential applications of such novel hybrid architectures include flexible solar cells, displays, and sensors.

Al(0.37)Ga(0.63)As nanowires (NWs) were grown in a molecular beam epitaxy system on GaAs(111)B substrates. Micro-photoluminescence measurements and energy dispersive X-ray spectroscopy indicated a core-shell structure and Al composition gradient along the NW axis, producing a potential minimum for carrier confinement. The core-shell structure formed during the growth as a consequence of the different Al and Ga adatom diffusion lengths., Comment: 20 pages, 7 figures