基于气液固机理的大批量InN纳米线生长

采用气液固机理生长了大批量均匀的InN纳米线,扫描电镜图像显示出这些光滑纳米线的平均直径和长度分别为65nm和15μm。高分辨透射电镜、选区电子衍射、微区拉曼散射光谱结合EDS能谱说明了纳米线为六方纤锌矿结构单晶,并证实了纳米线的生长遵循气液固生长机理。纳米线的光致发光光谱在1.89eV附近有一发光峰。改变NH3的流量可以调控纳米线的形貌和生长方向,我们从能量角度对此进行了解释。     

Synthesis and characterization of indium nitride nanowires by plasma-assisted chemical vapor deposition

High-quality indium nitride (InN) nanowires were synthesized in a high temperature furnace on Au-coated Si substrates through the reaction of indium metal vapor with highly reactive nitrogen radicals generated by N₂ plasma. Highly-reactive nitrogen radicals provided a wide process window for the synthesis of InN nanowires by lowering the process temperature to avoid the decomposition of InN. X-ray diffraction, transmission electron microscopy and Raman spectra further showed that the as-synthesized InN nanowires were perfect single crystallites of wurtzite structure with the growth direction along [110].     

Bidirectional growth of indium phosphide nanowires

We present a bidirectional growth mode of InP nanowires grown by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). We studied the effect of the supply ratio of DEZn ([DEZn]) on InP grown structure morphology and crystal structures during the SA-MOVPE. Two growth regimes were observed in the investigated range of the [DEZn] on an InP(111)B substrate. At low [DEZn], grown structures formed tripod structures featuring three nanowires branched toward the [111]A directions. At high [DEZn], we obtained hexagonal pillar-type structures vertically grown on the (111)B substrate. These results show that the growth direction changes from [111]A to [111]B as [DEZn] is increased. We propose a growth mechanism based on the correlation between the incident facet of rotational twins and the shapes of the grown structures. Our results bring us one step closer to controlling the direction of nanowires on a Si substrate that has a nonpolar nature. They can also be applied to the development of InP nanowire devices.     

Novel growth of aluminium nitride nanowires

This work describes novel growth of aluminium nitride (AIN) nanowires by nitridation of a mixture consists of aluminium and ammonium chloride powders (Al:NH4Cl = 1.5:1 weight ratio) at 1000 degrees C for 1 h in flowing nitrogen gas (1 l/min). XRD analysis of the product showed the formation of pure hexagonal AIN. SEM micrographs of as-synthesized product revealed the growth of homogeneous AIN nanowires (phi 40-150 nm). No droplets were observed at the tips of obtained nanowires which suggests that they were grown mainly by a vapor-phase reactions mechanism. Thermodynamic analysis of possible intermediate reactions in the operating temperatures range illustrates that these nanowires could be grown via spontaneous vapor-phase chlorination-nitridation sequences.     

Synthesis of long indium nitride nanowires with uniform diameters in large quantities

Large quantities of indium nitride (InN) nanowires are synthesized by the in situ nitriding of indium oxide (In(2)O(3)) powders in an ammonia (NH(3)) flux. Tens of milligrams of nanowires are obtained in one batch. Every 100 mg of In(2)O(3) starting powder can produce up to 65 mg of InN nanowires under the optimized conditions. The synthesized nanowires grow along the [001] direction with excellent crystallinity. They are of high purity and are 30-50 microm in length with an almost uniform diameter of about 100 nm. Photoluminescence measurements of the nanowires exhibit a strong peak at 707 nm. An optical bandgap of about 1.7 eV is estimated based on the absorption spectrum. The experimental results also demonstrate that the approach of nitriding In(2)O(3) powders in situ is feasible for the synthesis of high-purity InN nanowires in large quantities, with good reproducibility and without catalyst materials. The synthesis of InN nanowires in large quantities would be of benefit to the further study and understanding of their intrinsic properties, as well as being advantageous for their potential application in nanodevices.     

Electron transport within the wurtzite and zinc-blende phases of gallium nitride and indium nitride

Wide energy gap semiconductors are broadly recognized as promising materials for novel electronic and opto-electronic device applications. As informed device design requires a firm grasp on the material properties of the underlying electronic materials, the electron transport that occurs within the wide energy gap semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving and burgeoning field of research, we review analyzes of the electron transport within some wide energy gap semiconductors of current interest in this paper. In order to narrow the scope of this review, we will primarily focus on the electron transport that occurs within the wurtzite and zinc-blende phases of gallium nitride and indium nitride in this review, these materials being of great current interest to the wide energy gap semiconductor community; indium nitride, while not a wide energy gap semiconductor in of itself, is included as it is often alloyed with other wide energy gap semiconductors, the resultant alloy often being a wide energy gap semiconductor itself. The electron transport that occurs within zinc-blende gallium arsenide will also be considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, will also be provided. Steady-state and transient electron transport results are presented. The evolution of the field, a survey of the current literature, and some applications for the results presented herein, will also be featured. We conclude our review by presenting some recent developments on the electron transport within these materials. This review is the latest in a series of reviews that have been published on the electron transport processes that occur within the class of wide energy semiconductor materials. The results and references have been updated to include the latest developments in this rapidly evolving field of study.     

Zinc blende and wurtzite crystal phase mixing and transition in indium phosphide nanowires

Indium phosphide (InP) nanowires, which have crystal phase mixing and transition from zinc blende (ZB) to wurtzite (WZ), are grown in intermediate growth conditions between ZB and WZ by using selective-area metalorganic vapor phase epitaxy (SA-MOVPE). The shape of InP nanowires is tapered unlike ZB or WZ nanowires. A growth model has been developed for the tapered nanowires, which is simply described as the relationship between tapered angle and the ratio of ZB and WZ segments. In addition, the peak energy shift in photoluminescence measurement was attributed to the quantum confinement effect of the quantum well of the ZB region located in the polytypic structure of ZB and WZ in nanowires.     

Preparation of P-type indium phosphide films by close space vapor transport

InP films have been grown by close space transport employing 0.8 mol% PCl₃ in H₂. For deposition on InP single crystals, 700C source and 650C substrate temperatures produced epitaxial films on (100), polycrystalline films on (111)A, and powdery layers on (111)B. Growth rates are 6 to 10 |Gmm/hr on (100) InP and ~50 μm/hr on (111)A InP. Regardless of InP source doping, deposits exhibit net donor concentrations of 5×10¹⁷ to 1×10¹⁸cm^?3. Zn doping with 0.02 to 0.5 mol% Zn(C₂H₅)₂ in the gas phase resulted in partially compensated p-InP with net acceptor concentrations up to 7×10¹⁸cm^?3. Polycrystalline films have been grown on Mg-coated carbon or molybdenum substrates at 700C source and 590C substrate temperatures. Growth rates lie between 40 and 50 μm/hr. Substantial recrystallization and grain growth are observed after 2 day anneals at 950C under 5 atm of phosphorus.     

High crystal quality wurtzite-zinc blende heterostructures in metal-organic vapor phase epitaxy-grown GaAs nanowires

We have prepared GaAs wurtzite (WZ)-zinc blende (ZB) nanowire heterostructures by Au particle-assisted metal-organic vapor phase epitaxy (MOVPE) growth. Superior crystal quality of both the transition region between WZ and ZB and of the individual segments themselves was found for WZ-ZB single heterostructures. Pure crystal phases were achieved and the ZB segments were found to be free of any stacking defects, whereas the WZ sections showed a maximum stacking fault density of 20 μm⁻¹. The hexagonal cross-sectional wires are terminated by -type side facets for the WZ segment and predominantly {110}-type side facets for the ZB part of the wire. A diameter increase occurred after the transition from WZ to ZB. Additionally, facets of the -type as well as downwards-directed overgrowth of the WZ segments were formed at the WZ to ZB transition to compensate for the observed diameter increase and facet rotation. In the case of WZ-ZB multiple heterostructures, we observed slightly higher densities of stacking faults and twin planes compared to single heterostructures.      

Local vapor transport synthesis of zinc oxide nanowires for ultraviolet-enhanced gas sensing

A novel local vapor transport technique via induction heating is presented to enable selective, localized synthesis and self-assembly of nanowires, providing a simple and fast method for the direct integration of nanowires into functional devices. The single-crystalline zinc oxide (ZnO) nanowires are grown locally across the silicon-on-insulator microelectrodes within minutes, and the enhancement of gas sensing of ZnO nanowires is demonstrated under ultraviolet (UV) illumination at room temperature. Experiments indicate that when suspended nanowires are exposed to UV light, a twelve-fold increase in conductance and a near five-fold improvement in oxygen response are measured. Furthermore, the UV-enhanced transient responses exhibit a two-level photocurrent decay attributed to carrier recombination and oxygen readsorption. As such, the local vapor transport synthesis and UV-enhanced sensing scheme could provide a promising approach for the construction of miniaturized and highly responsive nanowire-based gas sensors.     

Mechanisms of reactive sputtering of indium II: Growth of indium oxynitride in mixed N2-O2 discharges

The reactive sputtering of indium in mixed N₂-O₂ discharges was investigated using in situ optical absorption and emission spectroscopic analyses of plasma processes. All measured discharge parameters including the target sputtering rate, the target current and the sputtered indium emission intensity and neutral atom density exhibited abrupt changes with oxygen concentration at a critical value C¹. For a total pressure of 50 mTorr C¹ was approximately 2.5 mol.%. The abrupt change was caused by the formation of an indium oxide layer on the target surface over a very narrow range of O₂ partial pressures. The nitrogen coverage on the target was small at all gas compositions because of rapid preferential sputtering.X-ray photoelectron spectroscopy, Auger electron spectroscopy and X-ray diffraction were used to characterize the deposited film chemistry and structure as functions of the growth conditions. All films were n-type semiconductors and could be classified into the following three groups: (1) films grown at 0<C₀₂<2.5 mol.% were InN-based alloys with the wurtzite structure containing oxygen in solid solution; (2) films grown at 2.5 mol.% <C_O2<6 mol.% were two-phase mixtures; (3) films grown at C_O2>6 mol.% were cubic In₂O₃-based alloys with nitrogen in solid solution. Optical band gap measurements showed that E_g ranged from 1.7 to 2.4 eV for films of type (1) and from 2.4 to 3.6 eV for films of type (3).     

Crystal growth of KCl in a reactive atmosphere II: The crystal growth technique

The crystal growth technique employed in the growth of large single crystals of KCl while the material is undergoing reactive-atmosphere processing is described in detail.     

One-step growth of curled GaN nanowires using chemical vapor deposition method

The studies of curled GaN nanowires grown on sapphire and silicon substrate using chemical vapor deposition method have been reported in this article. The mean diameters of the nanowires grown on sapphire and silicon were 108.1 nm and 98 nm respectively. A growth model was proposed to describe the growth of nanowires. X-ray diffraction pattern and Raman spectroscopy revealed that the nanowires were hexagonal wurtzite in structure. Gaussian fitting was done on photoluminescence spectra, which revealed two sub-bands that could be attributed to band emission and surface disorder caused by impurities. The absence of yellow luminescence signified undoped case and minimal shallow level defects.     

Mechanisms of crystal growth from fluxed melts

This review is mainly concerned with the basic mechanisms of crystal growth from the flux and with the origin of defects in these crystals. An outline is given of the theory of growth from solution and this is compared with experiments on aqueous solutions, which are the main source of data against which the validity of this theory may be tested. The analogy between aqueous solution and flux growth is discussed and estimates given for the rate at which crystals grown from the flux in the diffusion-controlled and particle integration-controlled limits. Studies of the surfaces of flux crystals favour a screw dislocation mode of growth, with propagation by a lateral spreading of layers rather than by spirals. The incidence of flux inclusions is discussed and related where possible to the conditions of growth.     

Effective growth of boron nitride nanotubes by thermal chemical vapor deposition

Effective growth of multiwalled boron nitride nanotubes (BNNTs) has been obtained by thermal chemical vapor deposition (CVD). This is achieved by a growth vapor trapping approach as guided by the theory of nucleation. Our results enable the growth of BNNTs in a conventional horizontal tube furnace within an hour at 1200?°C. We found that these BNNTs have an absorption band edge of 5.9?eV, approaching that of single h-BN crystals, which are promising for future nanoscale deep-UV light emitting devices.     

Controlled growth of ternary alloy nanowires using metalorganic chemical vapor deposition

We report the growth and characterization of ternary AlxGa1- xAs nanowires by metalorganic chemical vapor deposition as a function of temperature and V/III ratio. Transmission electron microscopy and energy dispersive X-ray spectroscopy show that, at high temperatures and high V/III ratios, the nanowires form a core-shell structure with higher Al composition in the nanowire core than in the shell. We develop a growth model that takes into account diffusion of reactants and decomposition rates at the nanowire catalyst and stem to describe the compositional difference and the shell growth rate. Utilizing this model, we have successfully grown compositionally uniform Al0.16Ga0.84As nanowires. The ability to rationally tune the composition of ternary alloy nanowires broadens the application range of nanowires by enabling more complex nanowire heterostructures.     

Investigation of indium oxide as a self-catalyst in ZnO/ZnInO heterostructure nanowires growth

We investigated the self-catalytic role of indium oxide in the growth process of ZnO/ZnInO heterostructure nanowires on Si(111). The prepared nanowires had hexagonal cross sections and were tapered with tip diameters of 90 ± 5 nm and base diameters of 230 ± 5 nm. Energy dispersive X-ray and field emission Auger spectroscopies indicated that the grown nanowires were heterostructures of ZnO and ZnInO. Analysis of the early growth process revealed that indium may play a self-catalytic role. Therefore, the vapor-liquid-solid mechanism is likely to be responsible for growth of ZnO/ZnInO nanowires. X-ray diffraction and room temperature photoluminescence (PL) data demonstrated that the presence of indium results in a decrease in nanowires' crystallinity. These wires produced a large PL emission peak in the ultraviolet (UV) region and a smaller peak in the green region of the electromagnetic spectrum. The UV peak of the ZnO/ZnInO nanowires is blue-shifted with respect to that of pure ZnO nanowires.     

Thermoelectric properties of individual single-crystalline PbTe nanowires grown by a vapor transport method

We report the thermoelectric performance of individual PbTe nanowires with sizes ranging from 76 to 436 nm grown from a vapor transport method that synthesizes high-quality, single-crystalline PbTe nanowires. Independent measurements of temperature-dependent Seebeck coefficient (S), thermal conductivity (κ) and electrical conductivity (σ) of individual PbTe nanowires were investigated. By varying the nanowire size, the simultaneous increase and decrease of S (-130 μV K(-1)) and κ (1.2 W m(-1) K(-1)), respectively, are achieved at room temperature. Our results demonstrate the enhanced thermoelectric properties of individual single-crystalline PbTe nanowires, compared to that of bulk PbTe, and can provide guidelines for future work on nanostructured thermoelectrics based on PbTe.