Article

Self-catalyzed growth of GaSb nanowires at low reaction temperatures

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Thermal decomposition of Lewis acid–base adducts [t-Bu3Ga-Sbi-Pr3] (1) and [t-Bu3Ga]2[Sb2Et4] (2) in closed glass ampoules at temperatures between 250 and 350°C yielded crystalline GaSb nanowires. Isolated GaSb nanowires were formed preferably at low decomposition temperatures, whereas dendritic-like growth was observed at higher decomposition temperatures. In addition, self-catalyzed growth of GaSb nanowires using 90nm-sized Ga droplets, which were pre-deposited on Si(100) substrates, was achieved with the distibine Sb2Et4 at 250°C.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... GaSb NWs were usually synthesized by molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), thermal decomposition or CVD methods with gold as the catalysts [4,9,[18][19][20]. For instance, Yu et al. [18] grew GaSb NWs on Si substrates by MBE technique. ...
... Fig. 1c is the SEM image of the asgrown GaSb NWs. NWs with tapered structures deposit on the whole substrate, which are analogous to the previous report [20]. The lengths of the tapered GaSb NWs are 10-20 µm and the diameters are several hundred nanometers varied along the length of the NWs. ...
Article
A simple self-catalyzed chemical vapor deposition process was conducted to synthesize single-crystalline GaSb nanowires, where Ga droplets were utilized as the catalysts. The as-grown GaSb nanowires exhibited typical p-type semiconductor behavior with the calculated hole mobility of about 0.042 cm² V⁻¹ s⁻¹ The photoresponse properties of the GaSb nanowires were studied by fabricating nanowire photodetectors on both rigid and flexible substrates. The results revealed that the photodetectors exhibited broad spectral response ranging from ultraviolet, visible, to near infrared region. For the device on rigid substrate, the corresponding responsivity and the detectivity were calculated to be 3.86×10³A W⁻¹ and 3.15×10¹³ Jones for 500 nm light, and 7.22×10²A W⁻¹ and 5.90×10¹² Jones for 808 nm light, respectively, which were the highest value compared with those of other reported Ga1−xInxAsySb1−y structure nanowires. Besides, the flexible photodetectors not only maintained the comparable good photoresponse properties as the rigid one, but also possessed excellent mechanical flexibility and stability. This study could facilitate the understanding on the fundamental characteristics of self-catalyzed grown GaSb nanowires and the design of functional nano-optoelectronic devices based on Gasb nanowires.
... Surface passivation plays a vital role in the mechanical stability of the NWs. There are many experimental studies of the different properties of GaSbNWs [6,10,21,22] but few theoretical ones of their electronic properties [23], and almost no investigations of their vibrational properties [14,24]. The proper understanding of the dependence of the vibrational properties of GaSbNWs on their diameter and surface passivation, can lead to a better implementation of these structures in different technologies. ...
Article
Gallium Antimonide nanowires (GaSbNWs) have attracted much attention due to their possible applications in mid infrared detectors, however, there are only few theoretical investigations about this material and almost none regarding its vibrational properties. In this work the phonon modes of GaSbNWs were studied using the density functional theory with the finite displacement supercell scheme. The nanowires are modeled by removing atoms outside from a circumference along the [1 1 1] direction. All surface dangling bonds were passivated with hydrogen atoms. The results show that the expected red-shift of the highest frequency modes of GaSb are hindered by low frequency H bond bending modes. Three clearly distinguishable frequency intervals were observed: One with vibrations whose main contribution come from the Ga and Sb nanowire atoms, the second interval with main contributions from H bending modes and finally a high frequency interval where the main contributions come from H stretching modes. Also, it was observed that the radial breathing mode (RBM) decreases when the nanowire diameter increases, while the contrary tendency is observed with their specific heat (the specific heat increases as the nanowire diameter increases), except in the low temperature region where the lower diameters have higher specific heat values. These results could be important for the characterization of these nanowires with IR and Raman techniques.
... There are various methods for the growth of semiconductor nanostructures e.g. molecular beam epitaxy (MBE) [5], metal organic chemical vapor deposition (MOCVD) [6], focused ion beam (FIB) [7,8], self-catalyzed growth [9] and ion irradiation [10][11][12][13][14][15][16][17]. Among these techniques, ion irradiation is a promising technique for the formation of semiconductor nanostructures, because it offers numerous advantages such as reproducibility of structure, precise control of ion fluence, energy and temperature, etc. Variation in the ion irradiation parameters like ion species, ion fluence, ion energy, incidence angle and temperature can result in different types of semiconductor nanostructures [10,11,13,17]. ...
Article
Full-text available
This paper presents formation of interconnected mesoporous structure using low energy (50 keV) Ar⁺-ion irradiation normal to the GaSb surface for the ion fluence 1 × 10¹⁶ and 5 × 10¹⁷ ions/cm². The surface morphology of pristine and ion irradiated samples was observed using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Depth profile of Ar⁺-ion distribution and cascade collisions with ion track in the irradiated GaSb epi-layer were simulated using stopping range ion in matter-transport range ion in matter (SRIM-TRIM) simulation. Presence of oxide phases such as gallium oxide (Ga2O3), antimony oxide (Sb2O3,) and elemental Sb in ion induced nanoporous GaSb structure is observed using X-ray photoelectron spectroscopy (XPS). The results are discussed using point defect formation mechanism during the ion irradiation process.
... There are various methods for the growth of semiconductor nanostructures e.g. molecular beam epitaxy (MBE) [5], metal organic chemical vapor deposition (MOCVD) [6], focused ion beam (FIB) [7,8], self-catalyzed growth [9] and ion irradiation [10][11][12][13][14][15][16][17]. Among these techniques, ion irradiation is a promising technique for the formation of semiconductor nanostructures, because it offers numerous advantages such as reproducibility of structure, precise control of ion fluence, energy and temperature, etc. Variation in the ion irradiation parameters like ion species, ion fluence, ion energy, incidence angle and temperature can result in different types of semiconductor nanostructures [10,11,13,17]. ...
... Although several methods can be used to fabricate nanoporous structures [10][11][12], ion implantation has been demonstrated to produce nanoporosity in various materials including GaSb [13,14], Ge [15,16], InSb [17], GaN [18] and, under special conditions, Si 1−x Ge x [19]. Ion implantation is a common method to introduce dopants in many semiconductor devices, but it also results in significant lattice disorder and defect formation [20]. ...
Article
Full-text available
We have studied the formation of porosity in crystalline GaAs0.25Sb0.75 and GaAs0.5Sb0.5 alloys under irradiation with 140 keV As⁻ ions over a wide range of temperature (−180 to 400 °C) and ion fluences ranging from to ions cm⁻². The GaAs0.25Sb0.75 alloy showed only little swelling (in comparison with GaSb), with void formation and sputtering both playing an important role in the materials modification. The initiation of voids and their evolution in the alloy strongly depends on the ion fluence and irradiation temperature, as well as the As content in the alloy. Porosity is largely suppressed in the GaAs0.25Sb0.75 alloy, with the major change being void formation. For the GaAs0.5Sb0.5 alloy, it was rendered amorphous with no apparent pores or void structures and only sputtering effects were observed at high ion fluence. In addition, the transformations from crystalline to amorphous and to a void or a porous structure occurred simultaneously in the GaAs0.25Sb0.75 alloy. The mechanisms responsible for such changes are consistent with point defect movement and segregation.
... As the continuous progresses in both the device applications and the fundamental research, growth of high material quality group III-antimonide nanowires is still on highly demanding. Sophisticated techniques have been exploited to grow high-quality group III-antimonide nanowires, such as metal-organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), and chemical beam epitaxy (CBE) [1,[10][11][12][13][14]. However, due to the high running cost and delicate growth conditions, the massive growth of long group III-antimonide nanowires in a reasonably low cost has been difficult with these expensive techniques [15,16]. ...
Article
Full-text available
We report on a simple but powerful approach to grow high material quality InSb and GaSb nanowires in a commonly used tube furnace setup. The approach employs a process of stable heating at a high temperature and then cooling down naturally to room temperature with the nanowire growth occurred effectively during the naturally cooling step. As-grown nanowires are analyzed using a scanning electron microscope and a transmission electron microscope equipped with an energy-dispersive X-ray spectroscopy setup. It is shown that the grown nanowires are several micrometers in lengths and are zincblende InSb and GaSb crystals. The FET devices are also fabricated with the grown nanowires and investigated. It is shown that the grown nanowires show good, desired electrical properties and should have potential applications in the future nanoelectronics and infrared optoelectronics.
... [9][10][11] GaSb nanowires have been grown by molecular beam epitaxy, 12 metallorganic chemical vapor deposition, 13 vapor-liquid-solid (VLS), 14 hot-wall chemical vapor deposition, 15 and so-called single source precursor. 9,16,17 Ultrasonic spray pyrolysis is a fabricated process characterized by a low temperature, low cost, and large area. This study examines the feasibility of fabricating GaSb nanowires on a (0002) sapphire substrate using catalysis-free ultrasonic spray pyrolysis. ...
Article
Full-text available
This study investigated the growth and characterization of gallium antimonide (GaSb) nanowires produced on sapphire substrates by catalysis-free ultrasonic spray pyrolysis. GaSb nanowires were obtained at deposition temperatures of 500 and 600 degrees C. The GaSb nanowires have an absorption edge at around 1.25 eV. The GaSb nanowires deposited at 500 degrees C had better transmittance at the high-energy region with wavelengths similar to 950 nm. An XRD peak was observed at 2 theta angles of 32.62 degrees, and it is considered to be associated with the GaSb (002) orientation based on linear fitting.
... Growth of GaAsSb nanowires in heterostructures with GaAs have been demonstrated using selfseeded epitaxy through the formation of Ga droplets (Figure 4c-d) [47]. There are also examples of self-seeded GaSb nanowire growth [68,60,69], which is mostly non-epitaxial. InSb nanowires have also been nucleated from In particles [55,69]. ...
Article
Full-text available
Antimonide semiconductors are suitable for low-power electronics and long-wavelength optoelectronic applications. In recent years research on antimonide nanowires has become a rapidly growing field, and nano-materials have promising applications in fundamental physics research, for tunnel field-effect transistors, and long-wavelength detectors. In this review, we give an overview of the field of antimonide nanowires, beginning with a description of the synthesis of these nano-materials. Here we summarize numerous reports on antimonide nanowire growth, with the aim to give an overall picture of the distinctive properties of antimonide nanowire synthesis. Secondly, we review the data on the physical properties and emerging applications for antimonide nanowires, focusing on applications in electronics and optics.
... [91] Consequently, distibines can be used in the Ga-assisted growth of GaSb nanowires at very low temperature of 250 8C (Figure 7). [92] In addition, the single-source precursor [tBu 3 Ga-SbiPr 3 ]was found suitable for the growth of GaSb nanowires at 350 8C in closed glass ampoules. ...
Article
General concepts for the synthesis and stabilization of low-valent organometallic complexes of Groups 2, 12, 13, and 15 metals and common structural motifs are described. While kinetically stabilized complexes are in the focus for more than two decades, the principle of base-stabilization only recently allowed the synthesis of unforeseen compounds. As-prepared complexes not only show fascinating structural diversities, but exhibit also very interesting chemical properties. Low-valent complexes are of particular interest in the synthesis of novel molecular complexes, but may also find applications as tailor-made precursors for the synthesis of nanosized materials.
Article
New findings in the coordination chemistry of neutral stibine and bismuthine ligands are reviewed. The article describes new ligand syntheses, coordination complexes of d-block and p-block elements with halostibines, halobismuthines, tertiary monostibines, tertiary bismuthines, distibines and hybrid polydentates containing antimony or bismuth. Current views on the nature of the M-Sb(Bi) bonds based upon X-ray structural studies and DFT calculations are discussed. The new work distinguishing metal stibine complexes from the chemistry of lighter phosphorus or arsenic ligands including, µ2- and µ3-bridging stibines, hypervalency and the oxidation of metal-coordinated stibines to stiboranyl or stiborane complexes, is also presented. Emerging applications of metal stibine complexes in catalysis, as reagents for the deposition of electronic materials and as anion sensors are illustrated. Literature coverage is from 2006 - early 2020.
Article
Mesoporous structures with interconnecting nanofibers (MSINs) are demonstrated by irradiating low energy (50, 75, and 100 keV) beams of Ar+\text{Ar}^+ -ions normal to the surface of molecular beam epitaxially grown gallium antimonide (GaSb) epi-layer on (100) oriented semi-insulating gallium arsenide (GaAs) substrates. The irradiation of 100 keV Ar+\text{Ar}^+ -ion beam with fluence of 1×1017 ions/cm21 \times 10^{17}\text{ ions/cm}^2 provides optimal and distinct nanofibrous network. A physical model illustrating the creation of point defects in the form of vacancies and interstitials, thus leading to mesoporous and interconnecting nanofiber structures with bombardment of energetic Ar+\text{Ar}^+ -ions onto GaSb surface, exhibits the surface evolution and formation of features in MSINs. The electron-microscopic, spectroscopic, and crystallographic analysis of the MSINs with distinct nanofibers network formed at optimized irradiation parameters, suggest presence of nanocrystallites, high degree of oxidation, co-existence of gallium oxide ( Ga2O3\text{Ga}_2 \text{O}_3 ) and antimony oxide ( Sb2O3, Sb2O5\text{Sb}_2 \text{O}_3,\text{ Sb}_2 \text{O}_5 ), and presence of elemental antimony (Sb) phase in the nanofiber interconnects.
Article
We here investigate the growth mechanism of Sn-seeded GaSb nanowires and demonstrate how the seed particle and its dynamics at the growth interface of the nanowire determine the polarity, as well as the formation of structural defects. We use aberration-corrected scanning transmission electron microscopy imaging methodologies to study the interrelationship between the structural properties, i.e. polarity, growth mechanism, and formation of inclined twin boundaries in pairs. Moreover, the optical properties of the Sn-seeded GaSb nanowires are examined. Their photoluminescence response is compared with one of their Au-seeded counterparts, suggesting the incorporation of Sn atoms from the seed particles into the nanowires.
Chapter
This chapter focuses solely on the metal-metal bonded compounds containing organometallic antimony or bismuth fragment. A review of the literature shows that metal-metal bonds involving antimony and bismuth are present in a plethora of organometallic derivatives and coordination complexes. The first part of the chapter is concerned with the chemistry of main group only compounds in which two or more antimony or bismuth atoms are covalently linked via single or multiple bonds. The second part of the chapter deals with the chemistry of transition metal complexes containing organometallic antimony or bismuth fragments in their coordination sphere. The chapter recognizes that stibines and bismuthines are donor ligands that interact with metal centers via coordination bonds. It documents chemistry of complexes featuring R2Pn, RPn. The chapter discusses recent advances made in the chemistry of complexes containing pentavalent antimony moieties bound to d-block metals.
Article
Full-text available
Room temperature implantation of 60 keV Arþ-ions in GaSb to the fluences of 7�1016 to 3�1018 ions cm�2 is carried out at two incidence angles, viz 0� and 60�, leading to formation of a nanoporous layer. As the ion fluence increases, patches grow on the porous layer under normal ion implantation, whereas the porous layer gradually becomes embedded under a rough top surface for oblique incidence of ions. Grazing incidence x-ray diffraction and cross-sectional transmission electron microscopy studies reveal the existence of nanocrystallites embedded in the ion-beam amorphized GaSb matrix up to the highest fluence used in our experiment. Oxidation of the nanoporous layers becomes obvious from x-ray photoelectron spectroscopy and Raman mapping. The correlation of ion-beam induced structural modification with photoluminescence signals in the infrared region has further been studied, showing defect induced emission of additional peaks near the band edge of GaSb.
Article
We report the systematic study of catalyst-free syntheses of InAs nanowires on Si substrates with various growth parameters and surface treatments. Nanowire morphology and crystal structure were studied using scanning electron microscopy and transmission electron microscopy. High-resolution cross-sectional transmission electron microscopy studies reveal heteroepitaxy of InAs[111] nanowires on Si(111) substrate with clean and sharp interface. Single nanowire field-effect transistor measurements of InAs nanowires under optimal growth conditions indicate a typical electron concentration of 1018–1019 cm–3 and mobility of around 1000 cm2/V·s. III/V on Si devices with InAs nanowire array on p-Si show a broadband photodetection up to wavelength of 3.5 μm.
Article
Full-text available
Room temperature irradiation of GaSb by 60 keV Ar+-ions at an oblique incidence of 60° leads to simultaneous formation of a nanoporous layer and undulations at the interface with the underlying substrate. Interestingly, with increasing ion fluence, a gradual embedding of the dense nanoporous layer takes place below ridge-like structures (up to the fluence of 1 × 1017 ions cm−2), which get extended to form a continuous layer (at fluences ≥4 × 1017 ions cm−2). Systematic compositional analyses reveal the co-existence of Ga2O3 and Sb2O3 in the surface layer. The results are discussed in terms of a competition between ion-induced defect accumulation and re-deposition of sputtered atoms on the surface.
Data
Full-text available
The role of Si during the metal−organic vapor phase epitaxy of GaN rods is investigated. Already a small amount of Si strongly enhances the vertical growth of GaN. Reactive ion etching experiments show that the inner volume of the rod is much more strongly etched than the m-plane surface layer. Transmission electron microscopy and energy dispersive X-ray spectroscopy measurements reveal that Si is predominiantly incorporated in the surface layer of the m-plane sidewall facets of the rods. The formation of a SiN layer prevents growth on and etching of the m-planes and enhances the mobility of atoms promoting vertical growth. Annealing experiments demonstrate the extraordinary thermal resistivity in comparison to undoped GaN rod structures and GaN layers. The subsequent InGaN quantum well growth on the GaN rods reveals the antisurfactant effect of the SiN layer. A model based on the vapor−liquid−solid growth mode is proposed. The results help to understand the role of Si during growth of GaN rod structures to improve the performance of rod based light emitting and electronic devices. ■ INTRODUCTION The group III nitrides are already used or are of general interest in various electronic and optoelectronic applications. 1 To reduce production costs of GaN based devices, the epitaxial growth on expensive GaN substrates has to be avoided. The heteroepitaxial growth of GaN layers, for example, on sapphire, suffers from a high density of defects generated at the sapphire−GaN interface. 2 An approach to eliminate these defects is the growth of GaN rods or wires with diameters in the nano-and micrometer range. In freestanding rods, bending of threading dislocations toward the sidewall facets occurs. 3,4
Article
Crystalline Ga2O3 nanowires are synthesized via an Au-catalyzed, as well as a self-catalyzed, growth by a low-temperature metal-organic (MO)CVD process using tBu3Ga as a novel Ga source. Morphology, elemental composition, and crystallinity of the resulting nanowires are analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and selected area electron diffraction (SAED). Photoluminescence (PL) spectra of the Ga2O3 nanowires show efficient defect-luminescence in the visible and UV ranges with blue and green emission peaks at 430 nm and 512 nm, respectively, at room temperature.
Article
The III-V nanowires (NWs) on Si are promising building blocks for future nanoscale electrical and optical devices on Si platforms. We review position-controlled growth of III-V NWs on Si substrate by selective-area growth and discuss how to control growth directions of III-V NW on Si. Finally, we demonstrate the integrations of III-V NW-based light-emitting diodes (LEDs) array on Si. These demonstrations should have broad applications in laser diodes and photodiodes with functionality not enabled by conventional NW.
Article
Charge transport of unintentionally doped GaSb nanowires was studied through the fabrication and analysis of nanowire field effect transistors (FETs). In this work, both temperature dependent and voltage dependent measurements demonstrate various operating regimes, including a transition from linear current-voltage behavior at low bias to a space-charge limited current (SCLC) at large bias. Analysis of the voltage and temperature variation in the SCLC regime provided quantitative information about the trap energy distribution in the nanowires, which, after thermal annealing, has been shown to reduce from 0.26 eV to 0.12 eV. The measurements also indicate that the GaSb nanowire FETs exhibit n-type behavior, which is likely due to oxygen impurities in the nanowires.
Article
We report on the growth of GaSb nanotrees on InAs { ̅1 ̅1 ̅1}(B) substrates by chemical beam epitaxy. GaSb nanotrees form by the nucleation of Ga droplets on the surface of < ̅1 ̅1 ̅1>(B) oriented GaSb nanowires followed by the epitaxial growth of branches catalyzed by these Ga droplets. In the tip region, the trunks of the GaSb nanotrees are periodically twinned, which is attributed to a change of the effective V/III ratio at the later stage of growth as a consequence of the change in surface structure. The reflectivity of a forest of nanotrees was measured for a broad spectral range and compared to the reflectivity of a GaSb ( ̅1 ̅1 ̅1)(B) wafer and of GaSb nanowires. At wavelengths from 500 to 1700 nm, the presence of GaSb nanotrees decreased the reflection by three orders of magnitude compared to a blank GaSb substrate.
Article
Full-text available
Until now, micrometer-scale or larger crystals of the III-V semiconductors have not been grown at low temperatures for lack of suitable crystallization mechanisms for highly covalent nonmolecular solids. A solution-liquid-solid mechanism for the growth of InP, InAs, and GaAs is described that uses simple, low-temperature (≤203°C), solution-phase reactions. The materials are produced as polycrystalline fibers or near-single-crystal whiskers having widths of 10 to 150 nanometers and lengths of up to several micrometers. This mechanism shows that processes analogous to vapor-liquid-solid growth can operate at low temperatures; similar synthesis routes for other covalent solids may be possible.
Article
Full-text available
To explain various temperature-dependent resistivity measurements [R(T)] on bismuth (Bi) nanowires as a function of wire diameter down to 7 nm, a semiclassical transport model is developed, which explicitly considers anisotropic and nonparabolic carriers in cylindrical wires, and the relative importance of various scattering processes. R(T) of 40 nm Bi nanowires with various Te dopant concentrations is measured and interpreted within this theoretical framework. © 2000 American Institute of Physics.
Article
Full-text available
Silicon nanowires will find applications in nanoscale electronics and optoelectronics both as active and passive components. Here, we demonstrate a low-temperature vapor–liquid–solid synthesis method that uses liquid-metal solvents with low solubility for silicon and other elemental semiconductor materials. This method eliminates the usual requirement of quantum-sized droplets in order to obtain quantum-scale one-dimensional structures. Specifically, we synthesized silicon nanowires with uniform diameters distributed around 6 nm using gallium as the molten solvent, at temperatures less than 400 °C in hydrogen plasma. The potential exists for bulk synthesis of silicon nanowires at temperatures significantly lower than 400 °C. Gallium forms a eutectic with silicon near room temperature and offers a wide temperature range for bulk synthesis of nanowires. These properties are important for creating monodispersed one-dimensional structures capable of yielding sharp hetero- or homointerfaces. © 2001 American Institute of Physics.
Article
Full-text available
We present a comprehensive, up-to-date compilation of band parameters for the technologically important III{endash}V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other. {copyright} 2001 American Institute of Physics.
Article
Full-text available
Recent advances in nonsilica fiber technology have prompted the development of suitable materials for devices operating beyond 1.55 μ m. The III–V ternaries and quaternaries (AlGaIn)(AsSb) lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices. Consequently, there has been tremendous upthrust in research activities of GaSb-based systems. As a matter of fact, this compound has proved to be an interesting material for both basic and applied research. At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication. This article presents an up to date comprehensive account of research carried out hitherto. It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility. An overview of the lattice, electronic, transport, optical and device related properties is presented. Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as for device applications are addressed. These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc. Several avenues where further work is required in order to upgrade this III–V compound for optoelectronic devices are listed. It is concluded that the present day knowledge in this material system is sufficient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication. © 1997 American Institute of Physics.
Article
Full-text available
We report near-infrared lasing in the telecommunications band in gallium antimonide semiconductor subwavelength wires. Our results open the possibility of the use of semiconductor subwavelength-wire lasers in future photonic integrated circuits for telecommunications applications.
Article
Full-text available
Reactive oxygen species (ROS) produced by mitochondria are potentially involved in the manifestation of methylmercury toxicity. However, the molecular mechanism underlying methylmercury toxicity remains poorly understood. We examined susceptibility to methylmercury in yeast strains that each lacked one of components of the mitochondrial electron transport system. Resistance to methylmercury was exhibited only by yeast that lacked Rip1, a component of electron transport system complex III. Resistance to methylmercury in Rip1-deficient yeast was independent of the activity of electron transport system complex III. Also, ROS levels induced by methylmercury in Rip1-deficient yeast were significantly lower than in wild-type yeast. Thus, Rip1 is potentially involved in ROS production through an as-yet unknown mechanism that is independent of the activity of electron transport system complex III, thereby enhancing methylmercury toxicity.
Article
Full-text available
A method combining laser ablation cluster formation and vapor-liquid-solid (VLS) growth was developed for the synthesis of semiconductor nanowires. In this process, laser ablation was used to prepare nanometer-diameter catalyst clusters that define the size of wires produced by VLS growth. This approach was used to prepare bulk quantities of uniform single-crystal silicon and germanium nanowires with diameters of 6 to 20 and 3 to 9 nanometers, respectively, and lengths ranging from 1 to 30 micrometers. Studies carried out with different conditions and catalyst materials confirmed the central details of the growth mechanism and suggest that well-established phase diagrams can be used to predict rationally catalyst materials and growth conditions for the preparation of nanowires.
Article
Full-text available
Electrically driven semiconductor lasers are used in technologies ranging from telecommunications and information storage to medical diagnostics and therapeutics. The success of this class of lasers is due in part to well-developed planar semiconductor growth and processing, which enables reproducible fabrication of integrated, electrically driven devices. Yet this approach to device fabrication is also costly and difficult to integrate directly with other technologies such as silicon microelectronics. To overcome these issues for future applications, there has been considerable interest in using organic molecules, polymers, and inorganic nanostructures for lasers, because these materials can be fashioned into devices by chemical processing. Indeed, amplified stimulated emission and lasing have been reported for optically pumped organic systems and, more recently, inorganic nanocrystals and nanowires. However, electrically driven lasing, which is required in most applications, has met with several difficulties in organic systems, and has not been addressed for assembled nanocrystals or nanowires. Here we investigate the feasibility of achieving electrically driven lasing from individual nanowires. Optical and electrical measurements made on single-crystal cadmium sulphide nanowires show that these structures can function as Fabry-Perot optical cavities with mode spacing inversely related to the nanowire length. Investigations of optical and electrical pumping further indicate a threshold for lasing as characterized by optical modes with instrument-limited linewidths. Electrically driven nanowire lasers, which might be assembled in arrays capable of emitting a wide range of colours, could improve existing applications and suggest new opportunities.
Article
Thermal decomposition reactions of the Lewis acid–base adducts t-Bu3Ga–Sb(t-Bu)31 and t-Bu3Ga–Sb(i-Pr)32 were investigated at different temperatures. Both adducts lead to the formation of crystalline GaSb particles in the temperature range of 275–450°C, proving their potential to serve as single source precursors for the preparation of GaSb. In contrast to 1, 2 tends to form crystalline, highly-oriented GaSb whiskers under the pyrolysis conditions. Detailed temperature-dependent studies clearly reveal the strong influence of the decomposition conditions on the whisker growth. While at temperatures between 275 and 375°C single GaSb needles preferably were formed, higher temperatures (400–450°C) lead to the formation of crystalline GaSb dendrites. As-prepared carbon-free, cubic GaSb whiskers were characterized in detail by SEM, TEM, electron diffraction, EDX and EEL spectroscopy.
Article
We present a focused ion beam based technique for the synthesis of nanowires in room temperature ambient without using any additional material source. Based on the idea of a catalytic approach gallium antimonide and antimony nanowires were grown with diameters of about 20 nm. We suppose that the intense focused ion beam exposure forms catalytic particles alloyed by the constituents of the growing nanowire in situ. In contrast to a broad class of techniques for nanowire growth neither heating of the sample nor any additional material source is required, thereby being compatible with on-chip microelectronics.
Article
ZnSe nano-wires (NWs) were fabricated on GaAs(1 1 1) and GaAs(1 1 0) substrates by the molecular beam epitaxy (MBE) technique via the vapor liquid solid (VLS) reaction. The size dependence of NW growth orientation was studied by varying the Au catalyst size. It was revealed that orientation is the preferred growth direction for NWs with size =>30 nm while NWs with size around 10 nm prefer to grow along the direction, with a small portion along the direction. A phenomenological model based on the principle that crystalline nucleation favors the minimum of the total system energy was proposed to explain these observations. An approach to achieve vertical NWs with size around 10 nm was demonstrated on a GaAs(1 1 0) substrate.
Article
Freestanding nanometer-scale whiskers composed of GaAs, InAs, and AlGaAs were grown using organometallic vapor-phase epitaxy. We found two kinds of relationship between the growth rate of the whiskers and their width depending on the growth temperature. The relationship between the growth rate and the width of the whiskers at lower temperatures can be explained by the difference between the chemical potentials in the vapor phase and in the whisker (solid phase). The minimum width of the whiskers was around 1 nm for GaAs, 4 nm for InAs, and 9 nm for AlGaAs. The relationship between the growth rate and the width of the whiskers at higher temperatures can be explained by the process of surface migration of the source material near the whiskers. In both relationships, the growth rate depended on the amount of Au in the alloy droplets used as seeds for growth. This dependence indicates that there is an optimum amount of Au for whisker growth. (c) 2005 The Electrochemical Society.
Article
The simple Lewis acid–base adducts (n-Bu)3Ga(SbR3) (R = Et 1, n-Pr 2, i-Pr 3, t-Bu 4) and (t-Bu)3Ga(SbR3) (R = Et 5, n-Pr 6, i-Pr 7, t-Bu 8) were prepared by combination of n-Bu3Ga or t-Bu3Ga, respectively, with the corresponding trialkylstibanes in a 1∶1 molar ratio. 1–8 were fully characterized by multinuclear NMR (1H and 13C) and mass spectroscopy. In addition, the solid state structures of 5 and 7 were determined by single crystal X-ray diffraction studies.
Article
Distibines Sb2R4 react with trimethylgallane and -indane (MMe3; M = Ga, In) with formation of heterocycles of the general type [Me2MSbR‘2]3 (R‘ = Me, M = Ga (2), In (3); R‘ = i-Pr, M = Ga (4)), whereas only decomposition reactions were observed for reactions with trialkylalanes. However, the mononuclear distibine−alane adduct [Al(t-Bu)3][Sb2(i-Pr)4] (1) with the distibine serving as monodentate ligand could be isolated and structurally characterized. In addition, reactions of the dibismuthine Bi2Et4 with M(t-Bu)3 (M = Al, Ga) were investigated, resulting in the formation of the simple Lewis acid−base adducts Et3Bi-M(t-Bu)3 (M = Al (5), Ga (6)). 1−6 were characterized by multinuclear NMR and mass spectroscopy and elemental analysis as well as single-crystal X-ray diffraction.
Article
Tetraalkyldistibanes Sb2R4 (R = nPr, iBu) react with tBu3M (M = Al, Ga) at –30 °C with the formation of the Lewis acid–base adducts [tBu3M]2[Sb2R4] [M = Al, R = nPr (1), iBu (2); M = Ga, R = nPr (3), iPr 4)]. Compounds 1 and 2 are stable in solution whereas 3 undergoes a Sb–Sb bond-breakage reaction with the subsequent formation of [tBu2GaSb(nPr)2]2 (5). The same trend was observed for the reaction of Sb2(iBu)4 with tBu3Ga, which yielded the heterocyclic stibanylgallane [tBu2GaSb(iBu)2]2 (6). In addition, the simple trialkylstibane adduct tBu3Al–Sb(iBu)3 (7) was obtained as a byproduct from the reaction of Sb2(iBu)4 with tBu3Al. Compounds 1–7 were characterized by multinuclear NMR (1H, 13C{1H}) and mass spectroscopy and elemental analysis. Compounds 1, 3, 5, and 7 were also investigated by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Article
The Fermi surface of antimony has been completely determined by the de Haas-van Alphen (dHvA) effect using the field-modulation measuring technique, modified to give strong dHvA period spectrometer action. The Fermi surface is found to consist of two sets of warped ellipsoids, the α set having a tilt angle of 53.0°±0.1°defined by the period maximum in the mirror plane, and the β set having a tilt angle of 87.7°±0.1°(angles are measured from ΓT in the sense toward ΓX). Carrier compensation has been established with the α set of carriers consisting of 6 pockets and the β set of 3 pockets. When the present results are compared with the recent band-structure calculations it is clear that the α carriers are the holes and the β carriers the electrons. This is the reverse of the conventional assumption for the signs of the carriers in antimony. The deviation of each set of pockets from ellipsoids has been accurately determined From the ellipsoidal approximation, the carrier concentration was found to be ne=(5.54±0.05)×1019 electrons/cm3 and nh=(5.49±0.03)×1019 holes/cm3. This new model removes the necessity for postulating a third band of carriers and is in agreement with all the previous experimental data. Comparison of the observed spin splitting with the electron-spin-resonance data of Datars gives new information on the angular variation of the g factor. Extra period branches have been observed along almost every field direction, but these have all been shown to arise from nonlinear mixing of strong dHvA period components.
Article
The use of metal organic vapor-phase epitaxy (MOVPE) for growth of one-dimensional nanostructures in the material systems GaAs, GaP, InAs and InP is investigated. Some kinetic effects are discussed, especially the general finding that in MOVPE thinner whiskers grow faster than thicker whiskers. Effects of growth temperature on growth rate and shape of the whiskers, the effects of different growth directions on the perfection of the materials and the possibilities to grow heterostructures in axial and lateral directions are reported. Ways to overcome the randomness in whisker growth by controlled seeding of the Au particles and by using lithography for site control are demonstrated.
Article
The following article is based on the Outstanding Young Investigator Award presentation given by Peidong Yang of the University of California, Berkeley, on April 14, 2004, at the Materials Research Society Spring Meeting in San Francisco.Yang was cited for "innovative synthesis of a broad range of nanowires and nanowire- heterostructure materials, and the discovery of optically induced lasing in individual nanowire devices." One-dimensional nanostructures are of both fundamental and technological interest. They not only exhibit interesting electronic and optical properties associated with their low dimensionality and the quantum confinement effect, but they also represent critical components in potential nanoscale devices. In this article, the vapor-liquid-solid crystal growth mechanism will be briefly introduced for the general synthesis of nanowires of different compositions, sizes, and orientation. Unique properties, including light-emission and thermoelectricity, will be discussed. In addition to the recent extensive studies on "single-component" nanowires, of increasing importance is incorporating different interfaces and controlling doping profiles within individual single-crystalline nanowires. Epitaxial growth plays a significant role in fabricating such nanowire heterostructures. Recent research on superlattice nanowires and other nanostructures with horizontal junctions will be presented. The implication of these heterojunction nanowires in light-emission and energy conversion will be discussed. Ways to assemble these one-dimensional nanostructures will also be presented.
Article
This paper reports galvanomagnetic properties of arrays of single-crystal bismuth nanowires, with diameters of 7 to 200 nm, embedded in an amorphous porous anodic alumina matrix. A sample preparation technique is described that makes it possible to obtain nanowires with diameters below 10 nm. The wires are single crystals, with their long axes oriented in the bisectrix/trigonal plane, about 19° from the bisectrix axis. The temperature dependence (1.4K<~T<~300K) of the electrical resistance, longitudinal magnetoresistance (0T<~B<~5T with 1.4<~T<~75K, and 0T<~B<~1T with 80<~T<~300K) and transverse magnetoresistance (0T<~B<~5T with 1.4<~T<~75K) of the nanowires are given. The results extend previous work to wires of narrower diameter, and confirm the existence of the semimetal-semiconductor phase transition seen in the magnetoresistance. The data are discussed qualitatively in terms of the interplay between the electron cyclotron radii, electron scattering on the wire walls, size-induced energy level quantization, and the transfer of carriers between the different carrier pockets of the Fermi surface. Nanowires of Bi are theoretically predicted to have a much higher thermoelectric figure of merit than bulk Bi.
Article
We have developed a technique for the synthesis of size-selected, GaAs, epitaxial nano-whiskers, grown on a crystalline substrate. As catalysts, we used size-selected gold aerosol particles, which enabled us to fully vary the surface coverage independently of the whisker diameter. The whiskers were rod shaped, with a uniform diameter between 10 and 50 nm, correlated to the size of the catalytic seed. Furthermore, by the use of nano-manipulation of the aerosol particles by means of atomic force microscopy, we can nucleate individual nano-whiskers in a controlled manner at specific positions on a substrate with accuracy on the nm level. © 2001 American Institute of Physics.
Article
We fabricated Bi nanowire array composites with wire diameters from 30 to 200 nm by high-pressure injection (HPI) of Bi melt into porous anodic alumina templates. The composites were dense, with Bi volume fraction in excess of 50%. The parallel Bi nanowires, whose length appeared to be limited only by the thickness of the host template (up to 55 μm), terminated at both sides of the composite in the Bi bulk. The individual Bi nanowire crystal structure was rhombohedral, with the same lattice parameters as that of bulk Bi; the wires in the array were predominantly oriented with the trigonal axis along the wire length. Low contact resistance was achieved by bonding the composite to copper electrodes.
Article
Reactions between distibanes of the type Sb2R4 and trialkylalanes and -gallanes R‘3M in 1:2 stoichiometry yield eight bisadducts of the type [Sb2R4][MR‘3]2 (R = Me, R‘ = t-Bu, M = Al 1, Ga 2; R = Et, M = Al, R‘ = Me 3, Et 4, t-Bu 5; M = Ga, R‘ = Me 6, Et 7, t-Bu 8), which were characterized by multinuclear NMR studies and elemental analysis. In addition, 1, 2, 5, and 8 are the first structurally characterized neutral main group Lewis acid−distibane bisadducts. 1−8 are unstable in solution toward the formation of heterocycles of the type [R2SbMR‘2]x. [Me2SbGa(t-Bu)2]3 (9) and [Et2SbGa(t-Bu)2]2 (10) have been isolated and their solid state structures determined by single-crystal X-ray diffraction.
Article
Single-crystal silicon nanowires with diameters approaching molecular dimensions were synthesized using gold nanocluster-catalyzed 1D growth. High-resolution transmission electron microscopy studies show that silicon nanowires grown with silane reactant in hydrogen are single crystal with little or no visible amorphous oxide down to diameters as small as 3 nm. Structural characterization of a large number of samples shows that the smallest-diameter nanowires grow primarily along the 110 direction, whereas larger nanowires grow along the 111 direction. In addition, cross-sectional transmission electron microscopy was used to address the importance of surface energetics in determining the growth direction of the smallest nanowires. The ability to prepare well-defined molecular-scale single-crystal silicon nanowires opens up new opportunities for both fundamental studies and nanodevice applications.
Article
We demonstrate a number of unseen self-assembled nanostructure complexes fabricated on various GaAs surface indexes by droplet epitaxy. Even under identical growth conditions, the configuration of nanostructure complexes is distinctive on each surface. The morphology evolution of nanostructure complexes is kinetically and energetically analyzed in determining the correlation between shape of nanostructure complexes and atomic surface matrixes with atomic ball−stick models. By systematically varying growth environment, we report many uncanny nanostructure complexes on given surface indexes.
Article
The bond dissociation energies of tetramethyl germane, triethyl stibine, tetraethyl lead, and triethylphosphine were determined using the technique of very‐low‐pressure pyrolysis. Arguments are presented for log A ≥ 17.0. The respective dissociation energies Δ H 298 are 83, 57, 54, and 68 (±2) kcal/mol. A consistent set of methyl bond energies to main group metals is determined from these and previous results, and is examined for trends. Bond energies for various radicals to tin are also derived.
Article
Semiconductor nanowires of III-V materials have generated much interest in recent years. However, the growth mechanisms by which these structures form are not well understood. The so-called vapor-liquid-solid (VLS) mechanism has often been proposed for III-V systems, with a chemically inert, liquid metal particle (typically Au) acting as a physical catalyst. We assert here that An is, in fact, not inert with respect to the semiconductor material but rather interacts with it to form a variety of intermetallic compounds. Moreover, we suggest that III-V nanowire growth can best be understood if the metallic particle is not a liquid, but a solid-phase solution or compound containing An and the group III material. The four materials GaP, GaAs, InP, and InAs will be considered, and growth behavior related to their particular temperature-dependent interaction with Au.
Article
Synthesis of nanowires of Group III antimonides (GaSb and InSb) is studied in detail using two approaches: (i) direct antimonidization of Group III metal droplets and (ii) reactive vapor transport of Group III metals in the presence of antimony in the vapor phase. The diameter of the GaSb nanowires ranged from 30 to 700 nm and length from a few to hundreds of micrometers. GaSb nanowires as long as 1 millimeter have been synthesized using direct antimonidization of large (several millimeters) sized gallium droplets. Reactive vapor transport of Group III metals in the presence of antimony in the vapor phase led to the formation of homoepitaxially oriented GaSb nanowire arrays on top of GaSb crystals. In the case of InSb, 100-nm-thick nanowires were obtained by direct antimonidization of indium droplets. Optical and electrical measurements of the GaSb nanowires, performed using photoluminescence and scanning tunneling spectroscopy, reveal a band gap of ∼0.72 eV, similar to that of bulk GaSb.
Article
Highly ordered near-stoichiometrical polycrystalline InSb nanowire arrays have been fabricated by direct current (dc) electrodeposition inside the nanochannels of anodic alumina membranes (AAMs) and subsequent annealing. X-ray diffraction patterns and X-ray energy dispersion analysis reveal the change of crystal structure and the ratio of indium to antimony due to the deposition potential. The results show that cubic-phase InSb nanowire arrays can be achieved by using certain deposition potential and subsequent annealing. Transmission electron microscopy and scanning electron microscopy results demonstrate that these InSb nanowires are uniform with diameters about 50 nm, corresponding to the pore diameter of the AAMs. Raman spectrum further demonstrates the InSb nanowire with high crystal quality. (c) 2005 The Electrochemical Society.
Article
A review and expansion of the fundamental processes of the vapor–liquid–solid (VLS) growth mechanism for nanowires is presented. Although the focus is on nanowires, most of the concepts may be applicable to whiskers, nanotubes, and other unidirectional growth. Important concepts in the VLS mechanism such as preferred deposition, supersaturation, and nucleation are examined. Nanowire growth is feasible using a wide range of apparatuses, material systems, and growth conditions. For nanowire growth the unidirectional growth rate must be much higher than growth rates of other surfaces and interfaces. It is concluded that a general, system independent mechanism should describe why nanowires grow faster than the surrounding surfaces. This mechanism is based on preferential nucleation at the interface between a mediating material called the collector and a crystalline solid. The growth conditions used mean the probability of nucleation is low on most of the surfaces and interfaces. Nucleation at the collector-crystal interface is however different and of special significance is the edge of the collector-crystal interface where all three phases meet. Differences in nucleation due to different crystallographic interfaces can occur even in two phase systems. We briefly describe how these differences in nucleation may account for nanowire growth without a collector. Identifying the mechanism of nanowire growth by naming the three phases involved began with the naming of the VLS mechanism. Unfortunately this trend does not emphasize the important concepts of the mechanism and is only relevant to one three phase system. We therefore suggest the generally applicable term preferential interface nucleation as a replacement for these different names focusing on a unifying mechanism in nanowire growth.
Article
We report the growth and characterization of GaSb nanowires grown by MOVPE. The structural properties of the nanowires are investigated by the means of transmission electron microscopy, X-ray diffraction and single nanowire photoluminescence. The measurements confirm a high material quality in the GaSb nanowires. Also, a back-gated nanowire transistor structure is used to extract values for the polarity and resistivity of the GaSb. Finally, a simple kinetic model is presented to explain the non-linear time dependence of the GaSb nanowire growth. (C) 2008 Elsevier B.V. All rights reserved.
Article
We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast to most other III-V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa-GaSb or AuGa2-GaSb pseudo-binaries of the Au-Ga-Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the 1 (1) over bar 0 side facets. (C) 2008 Elsevier B.V. All rights reserved.
Article
Ultrathin GaAs wires as thin as 15–40 nm and about 2 μm long have been grown on a GaAs substrate by metal‐organic vapor‐phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550 °C using trimethylgallium and arsine (AsH 3 ) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling‐bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc‐blende type for the growth temperature range of 460–500 °C, but it changes to the wurtzite type at 420 °C and temperatures higher than 500 °C. It is also found that the wires have a twin‐type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 to about 35 nm. In terms of luminescence polarization it is confirmed that the luminescence intensity parallel to the wires is four times greater than that perpendicular to the wires. These results clearly indicate the quantum‐size effect of carriers confined in the wire. As a preliminary application to devices, a p‐n junction has been formed along the GaAs wire. Light emission by current injection to the p‐n junction wires has been observed in continuous operation at room temperature.
Article
EMS is a set of computer programs which has been developed not only for the simulation and analysis of High-Resolution Electron Microscopy images, but also for the analysis of diffraction patterns. It is composed of small, dedicted tasks which have a well defined function. Schematically EMS can be divided into two parts. The first part is able to handle the typical calculations of crystallography encountered in electron microscopy such as automatic indexing of diffraction and Kikuchi patterns, simulation of spot and powder patterns, drawing of stereographic projections, calculation of the Bravais lattice of an unknown structure from two diffraction patterns, etc. The second part offers the possibility of the simulation of structure images of both perfect and defect structures using either a Fast-Fourier-Transform-based multislice approach or the Bloch wave formalism. The dialogue with EMS is “menu”-driven and completely interactive. Moreover numerous “note” and “help” files are available on-line for the convenience of the user.
Article
Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e., waveguiding). Combined with optical gain and suitable resonant feedback, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires. We have characterized the nanowire emission in detail with high-resolution optical microscopy. The waveguiding behavior of individual zinc oxide (ZnO) nanowires depends on the wavelength of the emitted light and the directional coupling of the photoluminescence (PL) to the emission dipoles of the nanowire. Polarization studies reveal two distinct regimes of PL characterized by coupling to either guided (bound) or radiation modes of the waveguide, the extent of which depends on wire dimensions. Pumping with high pulse energy engenders the transition from spontaneous to stimulated emission, and analysis of the polarization, line width, and line spacing of the laser radiation facilitates identification of the transverse and longitudinal cavity modes and their gain properties. Interpretation of the lasing spectra as a function of pump fluence, with consideration of ZnO material properties and ultrafast excitation dynamics, demonstrates a transition from exciton (fluence \textless 1 muJ/cm2) to electronhole plasma dynamics (fluence \textgreater 1 muJ/cm2) and gain saturation behavior (fluence \textgreater 3 muJ/cm2) modified by the constraints of the nanoscale cylindrical cavity.
Article
Interest in nanowires continues to grow because they hold the promise of monolithic integration of high-performance semiconductors with new functionality into existing silicon technology. Most nanowires are grown using vapour-liquid-solid growth, and despite many years of study this growth mechanism remains under lively debate. In particular, the role of the metal particle is unclear. For instance, contradictory results have been reported on the effect of particle size on nanowire growth rate. Additionally, nanowire growth from a patterned array of catalysts has shown that small wire-to-wire spacing leads to materials competition and a reduction in growth rates. Here, we report on a counterintuitive synergetic effect resulting in an increase of the growth rate for decreasing wire-to-wire distance. We show that the growth rate is proportional to the catalyst area fraction. The effect has its origin in the catalytic decomposition of precursors and is applicable to a variety of nanowire materials and growth techniques.
Article
The thermolysis behavior of tetramethyl- and tetraethyldistibine (Sb(2)Me(4) and Sb(2)Et(4)) was investigated using a mass spectrometer coupled to a tubular flow reactor under near-chemical vapor deposition (CVD) conditions. Sb(2)Me(4) undergoes a gas-phase disproportionation with an estimated activation energy of 163 kJ/mol. This reaction leads to the formation of methylstibinidine, SbMe, that reacts on the surface to produce antimony film and SbMe(3). Unfortunately, this clean decomposition pathway is limited to a narrow temperature range of 300-350 degrees C. At temperatures exceeding 400 degrees C, SbMe(3) decomposes following a radical route with a consequent risk of carbon contamination. In contrast, Sb(2)Et(4) disproportionates at the hot wall of the reactor. According to mass-spectrometric data, this reaction is significant starting at a temperature of 100 degrees C, with an apparent activation energy of 104 kJ/mol. Within the temperature range of 100-250 degrees C, the precursor decomposition leads to the formation of antimony films and SbEt(3), whereas different molecular reaction pathways are significantly activated above 250 degrees C. The use of Sb(2)Et(4) lowers the risk of carbon contamination compared to Sb(2)Me(4) at high temperature. Therefore, Sb(2)Et(4) is a promising CVD precursor for the growth of antimony films in the absence of hydrogen atmosphere in a wide temperature range.
Article
The Fermi surface of antimony has been completely determined by the de Haas-van Alphen (dHvA) effect using the field-modulation measuring technique, modified to give strong dHvA period spectrometer action. The Fermi surface is found to consist of two sets of warped ellipsoids, the α set having a tilt angle of 53.0°±0.1° defined by the period maximum in the mirror plane, and the β set having a tilt angle of 87.7°±0.1° (angles are measured from ΓT in the sense toward ΓX). Carrier compensation has been established with the α set of carriers consisting of 6 pockets and the β set of 3 pockets. When the present results are compared with the recent band-structure calculations it is clear that the α carriers are the holes and the β carriers the electrons. This is the reverse of the conventional assumption for the signs of the carriers in antimony. The deviation of each set of pockets from ellipsoids has been accurately determined From the ellipsoidal approximation, the carrier concentration was found to be ne=(5.54±0.05)×1019 electrons/cm3 and nh=(5.49±0.03)×1019 holes/cm3. This new model removes the necessity for postulating a third band of carriers and is in agreement with all the previous experimental data. Comparison of the observed spin splitting with the electron-spin-resonance data of Datars gives new information on the angular variation of the g factor. Extra period branches have been observed along almost every field direction, but these have all been shown to arise from nonlinear mixing of strong dHvA period components.
Article
A comparison is made between the conventional non-selective vapour-liquid-solid growth of InP nanowires and a novel selective-area growth process where the Au-seeded InP nanowires grow exclusively in the openings of a SiO(2) mask on an InP substrate. This new process allows the precise positioning and diameter control of the nanowires required for future advanced device fabrication. The growth temperature range is found to be extended for the selective-area growth technique due to removal of the competition between material incorporation at the Au/nanowire interface and the substrate. A model describing the growth mechanism is presented which successfully accounts for the nanoparticle size-dependent and time-dependent growth rate. The dominant indium collection process is found to be the scattering of the group III source material from the SiO(2) mask and subsequent capture by the nanowire, a process that had previously been ignored for selective-area growth by chemical beam epitaxy.
Article
Colloidal InAs quantum wires having diameters in the range of 5-57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution-liquid-solid (SLS) mechanism. The diameter dependence of the effective band gaps (DeltaE(g)s) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The DeltaE(g) values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d(-1)), whereas the simplest confinement models predict that DeltaE(g) should scale with inverse-square diameter (d(-2)). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band-conduction-band coupling in the narrow-gap InAs semiconductor.
Article
Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, <0001> oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.
Article
In this paper, we provide a theoretical basis using thermodynamic stability analysis for explaining the spontaneous nucleation and growth of a high density of 1-D structures of a variety of materials from low-melting metals such as Ga, In, or Sn. The thermodynamic stability analysis provides a theoretical estimate of the extent of supersaturation of solute species in molten metal solvent. Using the extent of maximum supersaturation, the size and density of critical nucleus were estimated and compared with experimental results using nucleation and growth of Ge nanowires using Ga droplets. The consistency of the proposed model is validated with the size and density of the resulting nanowires as a function of the synthesis temperature and droplet size. Both the experimental evidence and the theoretical model predictions point that the diameters of the resulting nanowires decrease with the lowering of synthesis temperatures and that the nucleation density decreases with the size of metal droplet diameter and increasing synthesis temperature.
Article
Nanoscale light-emitting diodes (nanoLEDs) with colors spanning from the ultraviolet to near-infrared region of the electromagnetic spectrum were prepared using a solution-based approach in which emissive electron-doped semiconductor nanowires were assembled with nonemissive hole-doped silicon nanowires in a crossed nanowire architecture. Single- and multicolor nanoLED devices and arrays were made with colors specified in a predictable way by the bandgaps of the III-V and II-VI nanowire building blocks. The approach was extended to combine nanoscale electronic and photonic devices into integrated structures, where a nanoscale transistor was used to switch the nanoLED on and off. In addition, this approach was generalized to hybrid devices consisting of nanowire emitters assembled on lithographically patterned planar silicon structures, which could provide a route for integrating photonic devices with conventional silicon microelectronics. Lastly, nanoLEDs were used to optically excite emissive molecules and nanoclusters, and hence could enable a range of integrated sensor/detection "chips" with multiplexed analysis capabilities.
Article
The epitaxial growth mechanism of truncated triangular III-V GaAs nanowires by metal-organic chemical vapor deposition (MOCVD) technique was analyzed. The single-crystalline wafers with deposited Au nanoparticles were placed in a growth chamber and the nanowire growth was initiated by the flow of vapor reactants at the growth temperature. GaAs nanowires were grown on a (111)B GaAs substrates in a horizontal-flow MOCVD reactor at a pressure of 100 mbar. The MOCVD results show that the size of the truncated triangular GaAs is larger than the hexagon in the top region of the nanowire indicating the lateral growth of (112) surfaces. The results also show that the type II positions on the (112) surface are the preferred lattice site of Ga atoms. The results also show that the hexagonal-shaped sidewalls are (112) atomic planes belong to (112)A and (112)B surfaces in the zinc blende structures.
Article
The vapor-liquid-solid (VLS) mechanism is most widely employed to grow nanowires (NWs). The mechanism uses foreign element catalytic agent (FECA) to mediate the growth. Because of this, it is believed to be very stable with the FECA-mediated droplets not consumed even when reaction conditions change. Recent experiments however differ, which suggest that even under cleanest growth conditions, VLS mechanism may not produce long, thin, uniform, single-crystal nanowires of high purity. The present investigation has addressed various issues involving fundamentals of VLS growth. While addressing these issues, it has taken into consideration the influence of the electrical, hydrodynamic, thermodynamic, and surface tension effects on NW growth. It has found that parameters such as mesoscopic effects on nanoparticle seeds, charge distribution in FECA-induced droplets, electronegativity of the droplet with respect to those of reactive nanowire vapor species, growth temperature, and chamber pressure play important role in the VLS growth. On the basis of an in-depth analysis of various issues, a simple, novel, malleable (SNM) model has been presented for the VLS mechanism. The model appears to explain the formation and observed characteristics of a wide variety of nanowires, including elemental and compound semiconductor nanowires. Also it provides an understanding of the influence of the dynamic behavior of the droplets on the NW growth. This study finds that increase in diameter with time of the droplet of tapered nanowires results primarily from gradual incorporation of oversupplied nanowire species into the FECA-mediated droplet, which is supported by experiments. It finds also that optimum compositions of the droplet constituents are crucial for VLS nanowire growth. An approximate model presented to exemplify the parametric dependency of VLS growth provides good description of NW growth rate as a function of temperature.
Article
The thermal decomposition of trimethylgallium (GaMe3), tris(tert-butyl)gallium (Gat Bu3) and triethylantimony (SbEt3) was investigated in a tubular hot-wall reactor coupled with a molecular-beam sampling mass spectrometer, and decomposition mechanisms were proposed. The obtained results confirm the predominance of the surface reactions and reveal that the radical decomposition path of Gat Bu3 and SbEt3, responsible for the formation of butane and ethane respectively, is restricted to a narrow temperature range in contrast to the molecular route that is responsible for the formation of the corresponding alkenes. GaMe3 decomposes above 480°C, forming essentially methane and also ethane to a lesser extent, whereas Gat Bu3 decomposes starting 260°C to form predominantly i-butane and i-butene as major species. The decomposition of SbEt3 starts at 400°C and forms n-butane, ethane, and ethene. The selectivity to n-butane increases with the thermolysis temperature. The resulting activation energies of the relevant decomposition paths show good agreement with those among them that have been measured before by temperature-programmed desorption techniques.
Article
Planar growth of high-quality InAs/InSb heterostructure nanowires by metal-organic vapor-phase epitaxy was demonstrated. The nanowires are found to consists of two-segment structure with a narrow base diameter and a wide upper-segment diameter. The InAs crystal structures show a very low density of stacking faults and the interface of InAs and InSb is atomically sharp as the lattice-fringe separation to the interface changes at the interface. Point analysis of the InAs segment gives a 49.5 to 50.5 ratio (∓0.6) between indium and arsenic, with no trace of any other material. It is found that the difference in indium concentration in the particle from 30 to 67 atomic percent would lead to an increase of the particle diameter of 35%. The 40-nm-long InAs zinc blende segment is present below the InAs/InSb interface and is thus assumed to correspond to the gas-switching sequence from arsenic to TMSb.