Vapor Growth Technique Research Articles

Revealing Seed-Mediated Structural Evolution of Copper-Silicide Nanostructures: Generating Structured Current Collectors for Rechargeable Batteries.

Metal silicide thin films and nanostructures typically employed in electronics have recently gained significant attention in battery technology, where they are used as active or inactive materials. However, unlike thin films, the science behind the evolution of silicide nanostructures, especially 1D nanowires (NWs), is a key missing aspect. Cux Siy nanostructures synthesized by solvent vapor growth technique are studied as a model system to gain insights into metal silicide formation. The temperature-dependent phase evolution of Cux Siy structures proceeds from Cu>Cu0.83 Si0.17 >Cu5 Si>Cu15 Si4 . The role of Cu diffusion kinetics on the morphological progression of Cu silicides is studied, revealing that the growth of 1D metal silicide NWs proceeds through an in situ formed, Cu seed-mediated, self-catalytic process. The different Cux Siy morphologies synthesized are utilized as structured current collectors for K-ion battery anodes. Sb deposited by thermal evaporation upon Cu15 Si4 tripod NWs and cube architectures exhibit reversible alloying capacities of 477.3 and 477.6 mAh g-1 at a C/5 rate. Furthermore, Sb deposited Cu15 Si4 tripod NWs anode tested in Li-ion and Na-ion batteries demonstrate reversible capacities of ≈518 and 495 mAh g-1 .

Terahertz Injection Lasers Based on a PbSnSe Solid Solution with an Emission Wavelength up to 50 μm and Their Application in the Magnetospectroscopy of Semiconductors

On the basis of a Pb1 –xSnxSe solid solution, long-wavelength diffusion injection lasers with laser generation up to a record long wavelength of 50.4 μm are created and studied. Pb1 –xSnxSe single crystals are grown from the vapor phase under the conditions of free growth (unseeded vapor-growth technique). By the example of a HgCdTe narrow-gap semiconductor and a quantum-well heterostructure, the possibility of applying the developed lasers in solid-state spectroscopy is demonstrated.

Si content variation and influence of deposition atmosphere in homoepitaxial Si-doped β-Ga2O3 films by pulsed laser deposition

Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 targets, respectively. A highest conductivity of 798 S cm−1 was achieved in films deposited at 550 °C–590 °C with targets of 0.05–1 wt. % SiO2. The electrically active and chemical Si content in films deposited at 550 °C was found to exceed the expected Si ablation target composition in all cases except the highest 1 wt. % SiO2 target attributed to imprecise target manufacturer compositional control at low SiO2 doping levels. Diminished electrical and structural quality films resulted from all targets at a 450 °C deposition temperature.

A review of Ga2O3 materials, processing, and devices

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (ε) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Терагерцовые инжекционные лазеры на основе твердого раствора PbSnSe с длиной волны излучения до 50 мкм и их использование для магнитоспектроскопии полупроводников

AbstractOn the basis of a Pb_1 –_ x Sn_ x Se solid solution, long-wavelength diffusion injection lasers with laser generation up to a record long wavelength of 50.4 μm are created and studied. Pb_1 –_ x Sn_ x Se single crystals are grown from the vapor phase under the conditions of free growth (unseeded vapor-growth technique). By the example of a HgCdTe narrow-gap semiconductor and a quantum-well heterostructure, the possibility of applying the developed lasers in solid-state spectroscopy is demonstrated.

Asymmetric waveguide and the dual-wavelength stimulated emission for CdS/CdS0.48Se0.52 axial nanowire heterostructures

Semiconductor axial nanowire heterostructures are important for realizing the high-performance nano-photonics and opto-electronics devices. Although different IV and III-V semiconductor axial nanowire heterostructures have been successfully prepared in recent decade, few of them focused on the optical properties, such as the waveguide, due to their low light emission efficiencies. The II-VI semiconductor nanowires grown by chemical vapor deposition strategy, such as CdS, CdSe and their alloys, can act as nanoscale waveguide, nanolasers, etc., because of their high optical gains and atomically smooth surfaces. However, it is still a challenge to growing the high-quality II-VI semiconductor axial nanowire heterostructures, owning to the poor controllability of the vapor growth techniques. Here, the CdS/CdSSe axial nanowire heterostructures are prepared with well controlled CVD method under the catalysis of annealed Au nanoparticles. The scanning electron microscope characterization shows that the wires have smooth surfaces with Au particles at the tips, indicating the vapor-liquid-solid growth mechanism for the nanowire heterostructures. The microscope images of the dispersed wires illuminated with a 405 nm laser show that the red and the green segment align axially with a sharp interface, demonstrating the axial alignment of CdS and CdSSe segments. The position related micro-photoluminescence spectra exhibit near band edge emissions of CdS and CdSSe without obvious emission from defect states, which suggests that the wires have highly crystalline quality. The waveguide of the nanowire heterostructures is studied through respectively locally exciting the two ends of the wire with a focused 488 nm laser. The local illuminations at both the CdS end and the CdSSe end result in red emission at the corresponding remote ends of the wires, with the emission intensity of the former being one order lower than that of the later, which is caused by the reabsorption of the green light emission (from CdS segment) in the CdSSe segment. This indicates the asymmetric waveguide in these heterosturctures, which implies that the CdS/CdSSe nanowire heterostructures have the potential applications in the photodiode. Under the pumping of 470 nm femtosecond laser, dual-color (red and green) lasing is realized based on these wires, with the lasing threshold of red light lasing being lower than that of the green one, which results from the larger round-trip loss for the green light arising from the self-absorption in CdSSe segment. To prove that the light can be transfer between the two segments with different refractivities, the waveguide of the nanowire heterostructure is simulated by the COMSOL. The result shows that the light can effectively propagate between CdS and CdSSe segments, which ensures the light-matter interaction in the axial CdS/CdSSe nanowire heterostructures as discussed above. These high-quality CdS/CdSSe axial nanowire heterostructures can be found to have the potential applications in photodiodes, dual-color nanolasers and photodetectors.

Chemiresistive sensing behavior of SnO2 (n)-Cu2O (p) core-shell nanowires.

We report the synthesis of SnO2-Cu2O n-p core-shell nanowires (C-S NWs) and their use as chemiresistive sensors for detecting trace amounts of gas. The n-p C-S NWs were synthesized by a two-step process, in which the core SnO2 nanowires were prepared by the vapor growth technique and subsequently the Cu2O shell layers were deposited by atomic layer deposition. A systematic investigation of the sensing capabilities of the n-p C-S NWs, particularly as a function of shell thickness, revealed the underlying sensing mechanism. The radial modulation of the hole-accumulation layer is intensified under shells thinner than the Debye length. On the other hand, the contribution of volume fraction to resistance modulation is weakened. By the combination of these two effects, an optimal sensing performance for reducing gases is obtained for a critical p-shell thickness. In contrast, the formation of p-shell layers deteriorates the NO2-sensing performance by blocking the expansion of the hole-accumulation layer due to the presence of p-n heterointerface.

High-Quality Large-Size Organic Crystals Prepared by Improved Physical Vapor Growth Technique and Their Optical Gain Properties

We have developed an improved physical vapor transport method. This method enables us to decrease the sublimation temperature of small organic molecules, and slow the weight loss process, and then regulate the degree of vapor saturation of materials. Large-size single-crystalline materials with high quality are successfully prepared from small organic functional molecules. The slice crystals are found to be single crystalline with high quality. The surface morphologies and structural information of grown crystals were characterized by optical microscope, atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. The results indicate that the growth mechanism of single crystals is a 2D nucleation, with elementary steps, large straight steps, and layer-by-layer growth.

Estimation of Interfacial and Adhesion Energies of Anthracene/Graphite (0001) system Based on Wulff's Theorem

The application of Wulff's theorem to an anthracene/graphite (0001) system is discussed in this paper. Anthracene crystals on a graphite (0001) substrate was prepared by using physical vapor growth technique with a horizontally arranged furnace. Many crystals showed line coincidences at the interface between crystals and graphite substrate;[010]anthracene//[21̄1̄0], [1̄21̄0], or [112̄0]graphite, and (100)anthracene//(0001)graphite, and a few maintained [010]anthracene//[21̄1̄0], [1̄21̄0], or [112̄0]graphite, and (001)anthracene//(0001)graphite. Most crystals grew as the typical Wulff's polygons on a graphite substrate and they kept the (100)anthracene/(0001)graphite relationship with cutting off near ha lf of the (001)anthracene plane. Such morphology enables the energetic estimation based on the Wulff's theorem. Resultantly, both interfacial and adhesion energies of the (100)anthracene/(0001)graphite system could be calculated to be 63.1 65.7 and 50.0 52.6 erg cm−2, respectively.

Morphologies of Pentacene Crystals Obtained by Physical Vapor Growth Technique

Three kinds of morphologies were observed in the pentacene crystals obtained by physical vapor growth, such as the whisker-type morphology, the plateletlike morphology with large parallelogram planes, and the plateletlike morphology with large dendritic planes. Plateletlike crystals have a common basal (001) plane, despite possessing different morphologies, that is, either the parallelogram or dendritic planes. The results of white-beam X-ray diffraction analysis revealed that the crystal qualities depended on the growth condition rather than on the crystal morphology.

N-type Lead-Chalcogenide Thermoelectric Materials Alloyed with Tin

AbstractN-type conduction was observed in epitaxial Pb1-xSnxSe and Pb1-xSnxTe thin films grown by MBE with an increasing charge carrier concentration as well as an increasing thermopower value related to an increasing tin content reaching up to 12at%. The lattice thermal conductivity decreases as expected due to alloy scattering but the carrier mobility is almost stable. All these effects increase strongly the thermoelectric properties of Pb1-xSnxSe and Pb1-xSnxTe. The n-type conduction arises from a metal excess in the stoichiometry range. The same type of conduction has also been found in bulk samples. Bulk single crystals of Pb1-xSnxSe and Pb1-xSnxTe are grown by the unseeded vapor growth technique. A rather constant mobility and a decreasing thermal conductivity with increasing tin content are measured in the n-type bulk samples. A figure of merit of ZT=0.9 was measured at 325°C for a Pb0,965Sn0,035Se sample with a carrier concentration of about 9.3E18 cm-3, i.e. already better than known n-type PbTe-based materials for this temperature range.

High-Quality Organic Single Crystalline Thin Films for Nonlinear Optical Applications by Vapor Growth

We report on the production of organic single crystalline thin films for integrated nonlinear optical applications by a vapor growth technique. The configurationally locked polyene chromophore 2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene} malononitrile (DAT2) that was used exhibits a noncentrosymmetric crystalline arrangement with monoclinic point group symmetry 2. It shows a second harmonic generation signal of about 2 orders of magnitude greater than that of urea. The grown DAT2 films are single crystalline and exhibit good optical quality and suitable size (area of ∼5 × 3 mm2 and the thickness in the range of 0.2−5 μm) for fabrication of photonic devices. Growth rates of a few hours have been achieved. Furthermore, the edges of the films are sharp and flat, which greatly reduces the additional processing requirements for applications.

Linear Arrangements of Anthracene Single Crystals on Muscovite (001) Substrate Constructed by Physical Vapor Growth Technique

The linear arrangement of anthracene single crystals on a muscovite (001) substrate was fabricated by the physical vapor growth technique. Most crystals clearly maintained epitaxial orientation relationships such as [010]anthracene∥[100], [110], or [110]muscovite, and (100)anthracene/(001)muscovite, and a few, (001)anthracene/(001)muscovite. The high periodicity of the (001)anthracene planes caused line coincidency with the highly periodically arranged atoms of the muscovite (001) substrate.

X-ray topography of polydiacetylene single crystals prepared by using physical vapor growth technique

The lattice defects in polydiacetylene (PDA) single crystals prepared using physical vapor growth were investigated by white beam X-ray topography. Line patterns along the [0 0 1] and [1 0 2] directions were clearly observed. Appearance of the line patterns along the [0 0 1] direction proves the polymerization direction predicted by Hädicke et al. The topographic results are in good agreement with the surface morphologies investigated by atomic force microscopy (AFM).

Epitaxial growth of anthracene single crystals on graphite (0 0 0 1) substrate with physical vapor growth technique

The epitaxial growth of an anthracene/graphite (0 0 0 1) system was performed using the physical vapor growth technique. Most anthracene single crystals had the clear tendency to form the epitaxial orientation relationships [0 1 0] anthracene// [ 2 1 ¯ 1 ¯ 0 ] , [ 1 ¯ 2 1 ¯ 0 ] , or [ 1 1 2 ¯ 0 ] graphite, (1 0 0) anthracene//(0 0 0 1) graphite, and a few, (0 0 1) anthracene//(0 0 0 1) graphite. The layer structure of each (0 0 1) plane of an anthracene single crystal appeared on lateral planes with a high periodicity, which caused epitaxy with the highly periodic atomic arrangement of a graphite (0 0 0 1) substrate.

Micromorphology of pure and PbI2‐doped CdI2 dendritic single crystals

AbstractUndoped and PbI2‐doped dendritic single crystals were grown by vapour growth technique. The basal surfaces of the as grown crystals were examined by optical and electron microscopy to observe wide variety of growth and defect features. Apart from typical features of dendritic growth, features of overgrowth, slip bands, growth steps and their bunching, etc. were observed. The basal surfaces of the crystals were then etched by controlled condensation of water vapour, after optimizing the etching condition, and the microscopic studies were repeated. Etch pits of hexagonal and triangular shape, both symmetric and asymmetric, and of different density, were observed in the case of undoped and doped crystals, respectively. In some cases, crystallographic hillocks were also observed. The crystals were also examined by X‐ray diffraction for their polytypism and related behaviour. The results are analyzed to elicit information on the correlation of structure, defects and surface features of the crystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of polydiacetylene single crystals based on physical vapor growth technique

We have succeeded in obtaining 10-mm-size polydiacetylene (PDA) single crystals using the physical vapor growth technique followed by the irradiation of ultraviolet (UV) rays, for the first time. The variety of growth conditions, such as growth temperature, growth time, carrier gases, and flow rate of gases are examined. Especially, the growth temperature and growth time have clear effects on the quality of crystals. Morphologies and sizes with relation to the various growth conditions are also observed. They show only one type of plateletlike shape with a pair of large parallelopiped planes, regardless of variety of growth conditions. The crystal thickness was estimated as about 500 nm by the observation of atomic force microscopy. The solubility of diacetylene (DA) and PDA to some organic solvents, and the X-ray diffraction data indicate that the obtained crystals are single crystals.

Photoluminescence study of a bulk vapour grown CdTe crystal

Low-temperature photoluminescence has been used to profile the distribution of impurities and defects through a CdTe boule grown at 700°C by the new “multi-tube” vapour-growth technique. The PL spectrum is dominated by an acceptor bound exciton band at 1.590 eV. We also observe eA 0 and DAP recombination. The Y luminescence band at 1.477 eV is also present and there are no other deep level bands observed. The identification of the luminescence bands is confirmed by temperature and intensity-dependent measurements and also by the strength of the phonon coupling. The PL data is used to map out the distribution of impurities and dislocations throughout the boule and supports previously published X-ray and defect etching data.

SiC Crystal Growth from the Vapor and Liquid Phase

ABSTRACTThe status of SiC vapor growth technique (PVT) is reviewed and related innovative aspects are introduced. Problems of the preparation of SiC crystals with uniform electronic properties are addressed, especially the growth of semiinsulating SiC. An overview about the performance of numerical modeling is given as tool for the optimization of the PVT process. Development activities in the field of liquid phase processing for the preparation of SiC bulk crystals and micropipe healing are presented. Finally recent results on the present understanding of filamentary void formation/elimination (micropipes, macrodefects) are summarized.

Characterisation of cadmium telluride bulk crystals grown by a novel “multi-tube” vapour growth technique

The structural properties of a boule of bulk cadmium telluride grown at the relatively low temperature of 700°C by a novel “multi-tube” vapour growth technique have been profiled in the growth direction by triple axis X-ray diffraction, defect revealing etching and photoluminescence. Considerable improvement in quality, as evidenced by a reduction in etch pit density and photoluminescence and X-ray linewidths, is observed through the boule.