GaAs Whiskers Research Articles

Peculiarities of magnetoresistance in GaAs whiskers at low temperatures

Magnetoresistance of GaAs whiskers with concentrations in the vicinity to metal-insulator transition (MIT) 1017–1018 cm−3 were studied at low temperatures and high magnetic fields (up to 14 T). The whiskers were doped with Te during the growth. The whisker diameter ranges from 10 to 40 μm. Temperature dependence of the whisker resistance have shown metallic and semiconductor character in the proximity to MIT from various sides of the transition. Depending on doping level the character of the whisker magnetoresistance changes from linear positive to quadratic negative. The magnetoresistance of metallic whiskers is explained in terms of weak antilocalization (WAL) model. The specimens with semiconductor character of conductance revealed negative magnetoresistance, magnitude of which rises due to moving away from MIT and reach 15% for the whiskers with concentration 1017 cm−3. The possible reasons of the negative magnetoresistance are discussed. The effect observed is attributed to weak localization (WL) of charge carriers in the region of hopping conductance for the whiskers in the vicinity to MIT. A high negative magnetoresistance (NMR) for the whiskers of low dopant concentration is connected with subsurface conductance in the disordered upper layers of the whiskers due to their core-shell structure.

Построение 2D-картин рентгеновской дифракции от модельных кристаллов-вискеров арсенида галлия

A set of GaAs whisker crystallites in the shape of hexagonal prism with the axis along the [111] direction have been modeled as well as constructions consisting of such prisms. For these model samples XRD patterns have been calculated. Basing on the calculated XRD pattern analysis, a fitting configuration of prismatic fragments has been built for an atomic array obtained with the help of applying molecular dynamics techniques to the initial model prismatic GaAs crystallite.

Simulating 2D-Diffraction Patterns of Model Gallium Arsenide Whisker Crystals

A set of GaAs whisker crystallites in the shape of hexagonal prism with the axisalong the [111] direction have been modeled as well as constructions consisting of such prisms. For these model samples XRD patterns have been calculated. Basing on the calculated XRD pattern analysis, a fitting configuration of prismatic fragments has been built for an atomic array obtained with the help of applying molecular dynamics techniques to the initial model prismatic GaAs crystallite. Keywords: whiskers, XRD pattern simulation, AIIIBV semiconductors, gallium arsenide.

Strain gages based on gallium arsenide whiskers

Strain-resistant properties of GaAs whiskers and ribbons of p- and n-type conductivity with various length (0.3–7 mm) and diameter (10–40 μm) have been investigated in a wide range of temperatures. Strain gages based on heavily doped p-type conductivity GaAs whiskers have linear deformation characteristics and a weak temperature dependence of strain sensitivity in the temperature range from –20 to +3500 °C. The temperature coefficient of resistance (TСR) of not fixed strain gages is about +(0.12–0.16)% × grad–1. The temperature coefficient of strain sensitivity is –0.03 % × deg–1 in the temperature range –120+800 °C. Strain gages based on n-type GaAs ribbons are characterized by high flexibility and high strain sensitivity. They are capable up to +4000 °C and can be used to measure deformations on curved surfaces at high temperatures. TСR of not fixed strain gages is –0.01 +0.03 % × grad–1. The temperature coefficient of strain sensitivity is –0.16% × deg–1 in the temperature range –120 ... +4000 °С.

A hybrid system of GaAs whisker nanocrystals and PbS quantum dots on silicon substrate

It is shown that a hybrid nanocomposite structure can be created by integration of semiconducting materials with different dimensionalities: an array of quasi-1D GaAs whisker nanocrystals formed by molecular-beam epitaxy on a Si (111) substrate and 0D PbS colloidal quantum dots. The morphological and spectral properties of the resulting system are analyzed.

Growth of single GaAs nanowhiskers on the tip of a tungsten needle and their electrical properties

A method for the formation of single GaAs semiconductor nanowhiskers and their assemblies on the tip of a chemically etched tungsten needle by molecular-beam epitaxy is proposed. The focused-ionbeam technique was used to separate a single nanowhisker. Electronic properties of single nanowhiskers were studied by elastic tunneling spectroscopy in ultrahigh vacuum. The band gap and the doping level of GaAs whiskers were determined using the current-voltage characteristics obtained from these measurements.

Deep microrelief measurement and stereo photography in scanning electron microscopy

Fundamental differences between standard photography and micro-object imaging in a scanning electron microscope are analyzed. Basic ways of taking stereograms with a scanning electron microscope by the object rotation method and the observing technique are described. It is shown that stereo photography correctly estimates the spatial arrangement of features in objects with an intricate microrelief and makes it possible to very accurately calculate the depth of this relief (which sometimes exceeds the field of vision at large magnifications) in wide limits (from 0.5 to 100.0 μm). Using the developed surface of Li4Ti5O12 oxide and GaAs whiskers as examples, a stereographic computational method based on linear measurements of the same area on the object before and after rotation is demonstrated.

Growth of one-dimensional III–V structures on Si nanowires and pre-treated planar Si surfaces

This paper presents a technique that allows the growth of epitaxial GaAs nanowires that are aligned to the crystal directions of the Si substrate. Low-pressure chemical vapor deposition (LP-CVD) grown Si nanowires were used as templates for molecular beam epitaxy (MBE) growth. The growth direction of the nanowires aligns with the [1 1 1] direction perpendicular to the Si substrate. After deposition of 200 nm GaAs in a solid source MBE system, we observed the formation of GaAs whiskers perpendicular to the {1 1 2} sidewalls of Si nanowires. By TEM analysis, the crystal structure of the GaAs nanostructures could be identified as wurtzite, where the growth axis of the wires was in the [0 0 0 1] direction. The whiskers are of good crystalline quality as no dislocations or stacking faults were observed in large areas by TEM, which makes these structures potential candidates for III–V integration on Si. In parallel to these experiments, we found a growth technique that allows GaAs nanowires to grow along the [1 1 1] direction of the planar Si [1 1 2] substrates. III–V nanowires with comparable geometry but higher density could be realized.

Nucleation at the lateral surface and the shape of whisker nanocrystals

A theoretical model of nucleation at the lateral surface of whisker nanocrystals during molecular-beam epitaxy and other high-vacuum deposition procedures is suggested. A model solution is obtained, which allows the calculation of the shape of whisker nanocrystals in relation to the diffusion flux of adatoms from the substrate surface to the base of the crystals. The temperature dependence of the nucleation effect is treated theoretically. It is shown that, at lowered surface temperatures, nucleation at the side walls results in the formation of cone-shaped crystals, with the length decreasing with decreasing temperature. The theoretical results are compared, at a qualitative level, with the experimental data for the GaAs whisker nanocrystals grown by molecular beam epitaxy on the Au-activated GaAs(111)As surface in the temperature range 400–600°C.

Growth of branched single-crystalline GaAs whiskers on Si nanowire trunks

In this paper we present the hetero-epitaxial growth of single-crystalline GaAs whiskers onSi(111)-nanowire trunks forming hierarchical star-like structures with a six-fold symmetry.These hierarchical nanostructures have been successfully formed utilizing bothvapor–liquid–solid (VLS) growth by low-pressure chemical vapor deposition (LPCVD) andmolecular-beam epitaxy (MBE) techniques. High-resolution transmission electronmicroscopy (HRTEM) studies revealed the [111] growth direction of the core Si nanowires(Si-NWs) with six {112} facet planes. The sequentially grown branches are single-crystallinehexagonal GaAs nanowhiskers which grow preferably in the [0001] direction and areperpendicular to the {112} facets of the Si-NW backbone. Photoluminescence (PL)measurements confirm the good crystalline quality of the GaAs nanowhiskers and ablueshift of about 30 meV compared to bulk zinc blende-type GaAs. The ability to preparerotationally branched NW structures should open new opportunities for both fundamentalresearch and applications including monolithic three-dimensional nanoelectronics andnanophotonics.

Effect of deposition conditions on nanowhisker morphology

The results of theoretical investigation of the effect of deposition conditions on the morphological properties of nanowhiskers (nanowires) in different growth technologies are presented. The dependences of the whisker length on their radius, temperatures, deposition rate, density, and average sizes of droplets (growth catalysts) are obtained. Effective adatom diffusion lengths on the substrate surface are determined under various growth conditions. Theoretical dependences of the nanowhisker length on radius and surface growth temperature are corroborated by experimental data obtained for GaAs whiskers grown by molecular-beam epitaxy on the Au-activated GaAs(111)As surface.

GaAs whiskers grown by metal-organic vapor-phase epitaxy using Fe nanoparticles

GaAs nanowhiskers were grown by metal-organic vapor-phase epitaxy on (111)B GaAs substrates. The diameter of the nanowhiskers was defined by monodisperse Fe nanoparticles deposited on the GaAs substrate from the vapor phase. The growth temperature of the whiskers was investigated from 480to520°C. The whiskers are preferentially directed along the crystal orientations of ⟨001⟩, ⟨111⟩, and their equivalents. High-resolution transmission electron microscopy characterization including energy disperse x-ray spectroscopy measurements revealed not only iron oxide but also arsenic inside the seed particle at the top of the GaAs whiskers. This indicates that the particle stays at the top during the whisker growth.

Current–voltage characteristics of GaAs nanowhiskers

Abstract The current–voltage characteristics of GaAs whiskers with an average diameter of 100 nm and a population of 100–1000 were measured using a device structure with two terminal electrodes. An ohmic contact to the tip of whiskers which were buried in spin-on glass between a metal electrode and n-type GaAs(1 1 1)As substrate was realized by heat treatment at 430 °C. The measured results show that the current–voltage curve for the whiskers is better approximated by the polynomial of the voltage to the power of 1.5 than by the exponential of the voltage. The dependence of the current on the voltage suggests that a space-charge layer was formed in the nanowhiskers. Step-like current fluctuations were also observed at 77 K, and this behavior was reproducible and unchanging even under a magnetic field. This suggests that the charge on the surface of the whiskers had a significant effect on carrier transport along the whiskers.

Properties of GaAs nanowhiskers grown on a GaAs(111)B surface using a combined technique

Arrays of GaAs whiskers on GaAs(111)B substrates were grown using a technique combining vacuum evaporation and molecular-beam epitaxy. The surface structural properties of the samples obtained were studied by scanning electron microscopy. It was found that the areal density of the whiskers amounted to (1–2)×109 cm−2. The typical dimensions of the whiskers were 30–150 nm (diameter) and 300–800 nm (length). It was shown that the whisker size can be controlled by changing the growth conditions and varying the thickness of the evaporated Au film.

Kinetic model of the growth of nanodimensional whiskers by the vapor-liquid-crystal mechanism

A new kinetic model describing the growth of nanodimensional whiskers according to the vapor-liquid-crystal (VLC) mechanism is proposed. A self-consistent equation determining the whisker growth rate as a function of the liquid drop radius and the growth conditions is obtained. A manifold increase in the growth rate on the drop containing an activating substance as compared to the case of growth on the nonactivated crystal surface is explained. The proposed approach generalizes the phenomenological Givargizov-Chernov model and allows the functional form and the kinetic coefficients in the dependence of the growth rate on the control and energy parameters to be determined. The results of numerical calculations of the whisker growth rate as a function of the drop radius for various growth conditions are presented and compared to experimental data on the growth of nanodimensional GaAs whiskers on gold-activated GaAs(111)B surface.

Electronic structure of nanometer-scale GaAs whiskers

We report a theoretical study of the electronic structure of GaAs nanowhiskers, grown in the [111] direction with hexagonal cross section, based on a tight binding approach. It is shown that the band structure of the GaAs nanowhiskers shifts from a direct band gap to an indirect band gap when the lateral size of the nanowhiskers becomes smaller than a certain value. The effective masses of the electrons and holes are shown to increase with decreasing the nanowhisker lateral size. It is also shown that the light-hole states appear to be at the top of the valence bands. The electrical and optical properties of the nanowhiskers are discussed in terms of the results of the calculations.

Growth and characterization of GaAs and InAs nano-whiskers and InAs/GaAs heterostructures

Semiconducting InAs and GaAs nano-whiskers have been grown using a chemical beam epitaxy approach in combination with size-selected catalytic Au aerosol particles. The characterization of InAs and GaAs whiskers shows high crystalline quality as seen by transmission electron microscopy. Gate-dependent transport measurements suggests a diffusive electronic transport mechanism. We have also combined these two material systems by growing a very abrupt heterostructure interface within the whiskers, allowing the growth of highly mismatched structures without misfit dislocations.

The role of gold clusters in semiconductor microstructure fabrication

Semiconductor wire-like microstructures with nanometer-scale dimensions have been grown by a selforganized technique. This fabrication is based on organometallic vapour-phase epitaxy (OMVPE). Gold is a key material for growing such nanometer-cylinders (called whiskers). Artificially controlling the gold deposition and the subsequent self-organized growth process resulted in successful control of diameter, length, and growth position of whiskers. Low-damage quantum-wire structures were fabricated which showed quantum confinement effects for electrons in quasi one-dimensional-structures. As an application of these structures, GaAs whiskers with p-n junctions were grown and used in quantum-wire light emitters.

Oxide-Assisted Semiconductor Nanowire Growth

Semiconductor wires with nanometer widths have attracted much attention in recent years for their potential applications in mesoscopic research and nanodevices. Since the 1960s, Si whiskers grown from the vapor-liquid-solid (VLS) reaction have been extensively studied. In the VLS reaction, Au particles are generally used as the mediating solvent on a Si substrate since Au and Si form a molten alloy at a relatively low temperature. Si in the vapor phase diffuses into the liquid-alloy droplet and bonds to the solid Si at the liquid-solid interface, which results in the growth of Si whiskers. The diameter of the whisker is determined by the diameter of the liquid-alloy droplet at its tip. Si whiskers generally grow along ⟨111⟩ directions epitaxially on Si(111) substrates in the form of single crystals by the VLS reaction.In different materials systems, however, a variety of whisker forms can be obtained. For example, GaP whiskers display rotational twins around their ⟨111⟩ growth axes, while GaAs whiskers grow in the form of the wurtzite structure.Thus far, the synthesis of one-dimensional nanostructured materials on a large scale remains a challenge. In recent years, many efforts have been made to synthesize Si nanowires by employing different methods such as photolithography and etching techniques and scanning tunneling microscopy. One method of particular interest is a recently developed laser ablation of metal-containing semiconductor targets, by which bulk quantities of semiconductor nanowires can be readily obtained. Our recent studies show that oxides play a dominant role in the nucleation and growth of high-quality semiconductor nanowires in bulk quantities by laser ablation, thermal evaporation, or chemical vapor deposition. A new growth mechanism called oxide-assisted nanowire growth has therefore been established. The ability to synthesize large quantities of high-purity (no contamination), ultra-long (in millimeters), and uniform-sized semiconductor nanowires (a few nanometers to tens of nanometers in diameter) from this new technique offers exciting possibilities in fundamental and applied research.

Gold cluster formation using an atomic force microscope and its applications to GaAs whisker growth

Au clusters were formed on the GaAs(111)B substrate by the field evaporation of Au atoms using an atomic force microscope (AFM). The obtained clusters appeared as mounds with typical diameters of 100–150 nm and heights of 1.5 nm. Furthermore, GaAs whiskers were grown after annealing by using these clusters as seeds. However, the sites of whiskers did not correspond to the sites of the Au clusters existing before annealing and growth. These results indicate that Au cluster formation by the AFM method did some damage to the substrate and permitted Au to diffuse into the substrate at relatively low temperatures.