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Hannah J Joyce - One of the best experts on this subject based on the ideXlab platform.
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a review of the electrical properties of semiconductor Nanowires insights gained from terahertz conductivity spectroscopy
Semiconductor Science and Technology, 2016Co-Authors: Hannah J Joyce, Jessica L. Boland, Chris Davies, Sarwat A Baig, Michael B JohnstonAbstract:© 2016 IOP Publishing Ltd. Accurately measuring and controlling the electrical properties of semiconductor Nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz (THz) conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of Nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of Nanowires using THz spectroscopy. A didactic description of THz time-domain spectroscopy, optical pump-THz probe spectroscopy, and their application to Nanowires is included. We review a variety of technologically important nanowire materials, including GaAs, InAs, InP, GaN and InN Nanowires, Si and Ge Nanowires, ZnO Nanowires, nanowire heterostructures, doped Nanowires and modulation-doped Nanowires. Finally, we discuss how THz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive THz receivers.
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ultralow surface recombination velocity in inp Nanowires probed by terahertz spectroscopy
Nano Letters, 2012Co-Authors: Hannah J Joyce, C Jagadish, J Wongleung, Qiang Gao, Hark Hoe Tan, Chaw Keong Yong, Callum J Docherty, Suriati Paiman, J Lloydhughes, Laura M HerzAbstract:Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP Nanowires. InP Nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP Nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite Nanowires. These findings show the great potential of very narrow InP Nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP Nanowires will be critical for future nanowire device engineering.
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tailoring gaas inas and ingaas Nanowires for optoelectronic device applications
IEEE Journal of Selected Topics in Quantum Electronics, 2011Co-Authors: Hannah J Joyce, J Wongleung, C JagadishAbstract:GaAs, InAs, and InGaAs Nanowires each exhibit significant potential to drive new applications in electronic and optoelectronic devices. Nevertheless, the development of these devices depends on our ability to fabricate these Nanowires with tight control over critical properties, such as nanowire morphology, orientation, crystal structure, and chemical composition. Although GaAs and InAs are related material systems, GaAs and InAs Nanowires exhibit very different growth behaviors. An understanding of these growth behaviors is imperative if high-quality ternary InGaAs Nanowires are to be realized. This report examines GaAs, InAs, and InGaAs Nanowires, and how their growth may be tailored to achieve desirable material properties. GaAs and InAs nanowire growth are compared, with a view toward the growth of high-quality InGaAs Nanowires with device-accessible properties.
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phase perfection in zinc blende and wurtzite iii v Nanowires using basic growth parameters
Nano Letters, 2010Co-Authors: Hannah J Joyce, J Wongleung, Qiang Gao, Hark Hoe Tan, C JagadishAbstract:Controlling the crystallographic phase purity of III-V Nanowires is notoriously difficult, yet this is essential for future nanowire devices. Reported methods for controlling nanowire phase require dopant addition, or a restricted choice of nanowire diameter, and only rarely yield a pure phase. Here we demonstrate that phase-perfect Nanowires, of arbitrary diameter, can be achieved simply by tailoring basic growth parameters: temperature and V/III ratio. Phase purity is achieved without sacrificing important specifications of diameter and dopant levels. Pure zinc blende Nanowires, free of twin defects, were achieved using a low growth temperature coupled with a high V/III ratio. Conversely, a high growth temperature coupled with a low V/III ratio produced pure wurtzite Nanowires free of stacking faults. We present a comprehensive nucleation model to explain the formation of these markedly different crystal phases under these growth conditions. Critical to achieving phase purity are changes in surface energy of the nanowire side facets, which in turn are controlled by the basic growth parameters of temperature and V/III ratio. This ability to tune crystal structure between twin-free zinc blende and stacking-fault-free wurtzite not only will enhance the performance of nanowire devices but also opens new possibilities for engineering nanowire devices, without restrictions on nanowire diameters or doping.
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novel growth phenomena observed in axial inas gaas nanowire heterostructures
Small, 2007Co-Authors: Mohanchand Paladugu, G.j. Auchterlonie, Hannah J Joyce, Chennupati JagadishAbstract:Growth behavior in Axial InAs/GaAs nanowire heterostructures was observed as they have important applications in optoelectronics. The physical phenomena, which resulted in the failure of axial InAs nanowire growth on GaAs Nanowires, was demonstrated. The vapor-liquid-solid (VPS) method was used for the growth of nanowire heterostructures. The changes in the growth directions of Nanowires were studied by Transmission electron microscopy (TEM), which lead to the growth failure of InAs Axial growth on the GaAs Nanowires. The catalyst used for the growth of the InAs/GaAs Nanowires was gold. TEM investigations have determined that the initial InAs clustering at the edge of an Au/GaAs interface results in Au particles that are unbalanced with the GaAs surface and wetting between the Au and the GaAs nanowire sidewalls results in the downward growth of InAs, in which InAs nanowire sections have an epitaxial relationship with GaAs sections.
Ze Zhang - One of the best experts on this subject based on the ideXlab platform.
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atomic scale observation of vapor solid nanowire growth via oscillatory mass transport
ACS Nano, 2016Co-Authors: Zhengfei Zhang, Yong Wang, Wentao Yuan, Xiao Feng Zhang, Chenghua Sun, Ze ZhangAbstract:In situ atomic-scale transmission electron microscopy (TEM) can provide critical information regarding growth dynamics and kinetics of Nanowires. A catalyst-aided nanowire growth mechanism has been well-demonstrated by this method. By contrast, the growth mechanism of Nanowires without catalyst remains elusive because of a lack of crucial information on related growth dynamics at the atomic level. Herein, we present a real-time atomic-scale observation of the growth of tungsten oxide Nanowires through an environmental TEM. Our results unambiguously demonstrate that the vapor–solid mechanism dominates the nanowire growth, and the oscillatory mass transport on the nanowire tip maintains the noncatalytic growth. Autocorrelation analysis indicates that adjacent nucleation events in the nanowire growth are independent of each other. These findings may improve the understanding of the vapor–solid growth mechanism of Nanowires.
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size dependent bandgap modulation of zno Nanowires by tensile strain
Nano Letters, 2012Co-Authors: Bin Wei, Ze Zhang, Kun Zheng, Yuefei Zhang, Xiaodong HanAbstract:We quantified the size-dependent energy bandgap modulation of ZnO Nanowires under tensile strain by an in situ measurement system combining a uniaxial tensile setup with a cathodoluminescence spectroscope. The maximal strain and corresponding bandgap variation increased by decreasing the size of the Nanowires. The adjustable bandgap for the 100 nm nanowire caused by a strain of 7.3% reached approximately 110 meV, which is nearly double the value of 59 meV for the 760 nm nanowire with a strain of 1.7%. A two-step linear feature involving bandgap reduction caused by straining and a corresponding critical strain was identified in ZnO Nanowires with diameters less than 300 nm. The critical strain moved toward the high strain level with shrunken Nanowires. The distinct size effect of strained Nanowires on the bandgap variation reveals a competition between core-dominated and surface-dominated bandgap modulations. These results could facilitate potential applications involving nanowire-based optoelectronic devi...
Benjamin J Wiley - One of the best experts on this subject based on the ideXlab platform.
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effects of length dispersity and film fabrication on the sheet resistance of copper nanowire transparent conductors
Nanoscale, 2015Co-Authors: James W Borchert, Aaron R Rathmell, Benjamin J Wiley, Ian E Stewart, Karen I WineyAbstract:Development of thin-film transparent conductors (TC) based on percolating networks of metal Nanowires has leaped forward in recent years, owing to the improvement of nanowire synthetic methods and modeling efforts by several research groups. While silver Nanowires are the first commercially viable iteration of this technology, systems based on copper Nanowires are not far behind. Here we present an analysis of TCs composed of copper nanowire networks on sheets of polyethylene terephthalate that have been treated with various oxide-removing post treatments to improve conductivity. A pseudo-2D rod network modeling approach has been modified to include lognormal distributions in length that more closely reflect experimental data collected from the nanowire TCs. In our analysis, we find that the copper nanowire TCs are capable of achieving comparable electrical performance to silver nanowire TCs with similar dimensions. Lastly, we present a method for more accurately determining the nanowire area coverage in a TC over a large area using Rutherford Backscattering Spectrometry (RBS) to directly measure the metal content in the TCs. These developments will aid research and industry groups alike in the characterization of nanowire based TCs.
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metal nanowire networks the next generation of transparent conductors
Advanced Materials, 2014Co-Authors: Aaron R Rathmell, Zuofeng Chen, Ian E Stewart, Benjamin J WileyAbstract:There is an ongoing drive to replace the most common transparent conductor, indium tin oxide (ITO), with a material that gives comparable performance, but can be coated from solution at speeds orders of magnitude faster than the sputtering processes used to deposit ITO. Metal Nanowires are currently the only alternative to ITO that meets these requirements. This Progress Report summarizes recent advances toward understanding the relationship between the structure of metal Nanowires, the electrical and optical properties of metal Nanowires, and the properties of a network of metal Nanowires. Using the structure–property relationship of metal nanowire networks as a roadmap, this Progress Report describes different synthetic strategies to produce metal Nanowires with the desired properties. Practical aspects of processing metal Nanowires into high-performance transparent conducting films are discussed, as well as the use of nanowire films in a variety of applications.
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copper nanowire networks with transparent oxide shells that prevent oxidation without reducing transmittance
ACS Nano, 2014Co-Authors: Zuofeng Chen, Ian E Stewart, Benjamin J WileyAbstract:Transparent conducting films of solution-synthesized copper Nanowires are an attractive alternative to indium tin oxide due to the relative abundance of Cu and the low cost of solution-phase nanowire coating processes. However, there has to date been no way to protect Cu Nanowires with a solution-phase process that does not adversely affect the optoelectric performance of Cu nanowire films. This article reports that the electrodeposition of zinc, tin, or indium shells onto Cu Nanowires, followed by oxidation of these shells, enables the protection of Cu nanowire films against oxidation without decreasing film performance.
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integrating simulations and experiments to predict sheet resistance and optical transmittance in nanowire films for transparent conductors
ACS Nano, 2013Co-Authors: Rose M Mutiso, Aaron R Rathmell, Benjamin J Wiley, Michelle C Sherrott, Karen I WineyAbstract:Metal nanowire films are among the most promising alternatives for next-generation flexible, solution-processed transparent conductors. Breakthroughs in nanowire synthesis and processing have reported low sheet resistance (Rs ≤ 100 Ω/sq) and high optical transparency (%T > 90%). Comparing the merits of the various Nanowires and fabrication methods is inexact, because Rs and %T depend on a variety of independent parameters including nanowire length, nanowire diameter, areal density of the Nanowires and contact resistance between Nanowires. In an effort to account for these fundamental parameters of nanowire thin films, this paper integrates simulations and experimental results to build a quantitatively predictive model. First, by fitting the results from simulations of quasi-2D rod networks to experimental data from well-defined nanowire films, we obtain an effective average contact resistance, which is indicative of the nanowire chemistry and processing methods. Second, this effective contact resistance i...
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the effect of nanowire length and diameter on the properties of transparent conducting nanowire films
Nanoscale, 2012Co-Authors: Stephen M Bergin, Patrick Charbonneau, Aaron R Rathmell, Yuhui Chen, Zhiyuan Li, Benjamin J WileyAbstract:This article describes how the dimensions of Nanowires affect the transmittance and sheet resistance of a random nanowire network. Silver Nanowires with independently controlled lengths and diameters were synthesized with a gram-scale polyol synthesis by controlling the reaction temperature and time. Characterization of films composed of Nanowires of different lengths but the same diameter enabled the quantification of the effect of length on the conductance and transmittance of silver nanowire films. Finite-difference time-domain calculations were used to determine the effect of nanowire diameter, overlap, and hole size on the transmittance of a nanowire network. For individual Nanowires with diameters greater than 50 nm, increasing diameter increases the electrical conductance to optical extinction ratio, but the opposite is true for Nanowires with diameters less than this size. Calculations and experimental data show that for a random network of Nanowires, decreasing nanowire diameter increases the number density of Nanowires at a given transmittance, leading to improved connectivity and conductivity at high transmittance (>90%). This information will facilitate the design of transparent, conducting nanowire films for flexible displays, organic light emitting diodes and thin-film solar cells.
C Jagadish - One of the best experts on this subject based on the ideXlab platform.
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ultralow surface recombination velocity in inp Nanowires probed by terahertz spectroscopy
Nano Letters, 2012Co-Authors: Hannah J Joyce, C Jagadish, J Wongleung, Qiang Gao, Hark Hoe Tan, Chaw Keong Yong, Callum J Docherty, Suriati Paiman, J Lloydhughes, Laura M HerzAbstract:Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP Nanowires. InP Nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP Nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite Nanowires. These findings show the great potential of very narrow InP Nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP Nanowires will be critical for future nanowire device engineering.
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tailoring gaas inas and ingaas Nanowires for optoelectronic device applications
IEEE Journal of Selected Topics in Quantum Electronics, 2011Co-Authors: Hannah J Joyce, J Wongleung, C JagadishAbstract:GaAs, InAs, and InGaAs Nanowires each exhibit significant potential to drive new applications in electronic and optoelectronic devices. Nevertheless, the development of these devices depends on our ability to fabricate these Nanowires with tight control over critical properties, such as nanowire morphology, orientation, crystal structure, and chemical composition. Although GaAs and InAs are related material systems, GaAs and InAs Nanowires exhibit very different growth behaviors. An understanding of these growth behaviors is imperative if high-quality ternary InGaAs Nanowires are to be realized. This report examines GaAs, InAs, and InGaAs Nanowires, and how their growth may be tailored to achieve desirable material properties. GaAs and InAs nanowire growth are compared, with a view toward the growth of high-quality InGaAs Nanowires with device-accessible properties.
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phase perfection in zinc blende and wurtzite iii v Nanowires using basic growth parameters
Nano Letters, 2010Co-Authors: Hannah J Joyce, J Wongleung, Qiang Gao, Hark Hoe Tan, C JagadishAbstract:Controlling the crystallographic phase purity of III-V Nanowires is notoriously difficult, yet this is essential for future nanowire devices. Reported methods for controlling nanowire phase require dopant addition, or a restricted choice of nanowire diameter, and only rarely yield a pure phase. Here we demonstrate that phase-perfect Nanowires, of arbitrary diameter, can be achieved simply by tailoring basic growth parameters: temperature and V/III ratio. Phase purity is achieved without sacrificing important specifications of diameter and dopant levels. Pure zinc blende Nanowires, free of twin defects, were achieved using a low growth temperature coupled with a high V/III ratio. Conversely, a high growth temperature coupled with a low V/III ratio produced pure wurtzite Nanowires free of stacking faults. We present a comprehensive nucleation model to explain the formation of these markedly different crystal phases under these growth conditions. Critical to achieving phase purity are changes in surface energy of the nanowire side facets, which in turn are controlled by the basic growth parameters of temperature and V/III ratio. This ability to tune crystal structure between twin-free zinc blende and stacking-fault-free wurtzite not only will enhance the performance of nanowire devices but also opens new possibilities for engineering nanowire devices, without restrictions on nanowire diameters or doping.
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influence of nanowire density on the shape and optical properties of ternary ingaas Nanowires
Nano Letters, 2006Co-Authors: Hannah J Joyce, Mohanchand Paladugu, C Jagadish, Alexandra SuvorovaAbstract:We have synthesized ternary InGaAs Nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the Nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs Nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs Nanowires.
Charles M. Lieber - One of the best experts on this subject based on the ideXlab platform.
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nanowire transistor performance limits and applications
IEEE Transactions on Electron Devices, 2008Co-Authors: Ping Xie, Charles M. LieberAbstract:Semiconductor Nanowires represent unique materials for exploring phenomena at the nanoscale. Developments in nanowire growth have led to the demonstration of a wide range of nanowire materials with precise control of composition, morphology, and electrical properties, and it is believed that this excellent control together with small channel size could yield device performance exceeding that obtained using top-down techniques. Here, we review advances in chemically synthesized semiconductor Nanowires as nanoelectronic devices. We first introduce basic nanowire field-effect transistor structures and review results obtained from both p- and n-channel homogeneous composition Nanowires. Second, we describe nanowire heterostructures, show that by using nanowire heterostructures, several limiting factors in homogeneous nanowire devices can be mitigated, and demonstrate that nanowire transistor performance can reach the ballistic limit and exceed state-of-the-art planar devices. Third, we discuss basic methods for organization of Nanowires necessary for fabricating arrays of device and circuits. Fourth, we introduce the concept of crossbar nanowire circuits, discuss results for both transistor and nonvolatile switch devices, and describe unique approaches for multiplexing/demultiplexing enabled by synthetically coded nanowire. Fifth, we discuss the unique application of thin-film nanowire transistor arrays on low-cost substrates and illustrate this with results for relatively high-frequency ring oscillators and completely transparent device arrays. Finally, we describe 3-D heterogeneous integration that is uniquely enabled by multifunctional Nanowires within a bottom-up approach.
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ge si nanowire heterostructures as high performance field effect transistors
Nature, 2006Co-Authors: Jie Xiang, Yongjie Hu, Yue Wu, Wei Lu, Charles M. LieberAbstract:Field-effect transistors (FETs) based on semi-conductor Nanowires could one day replace standard silicon MOSFETs in miniature electronic circuits. MOSFETs, or metal-oxide semiconductor field-effect transistors, are a type of transistor used for high-speed switching and in a computer's integrated circuits. A specially designed nanowire with a germanium shell and silicon core has shown promise as a nanometre-scale field-effect transistor: it has a near-perfect channel for electronic conduction. Now, in transistor configuration, this germanium/silicon nanowire is shown to have properties including high conductance and short switching time delay that are better than state-of-the-art silicon MOSFETs. In a transistor configuration, a new germanium/silicon nanowire has characteristics such as conductance, on-current and switching time delay that are better than those of state-of-the-art silicon metal-oxide-semiconductor field-effect transitors. Semiconducting carbon nanotubes1,2 and Nanowires3 are potential alternatives to planar metal-oxide-semiconductor field-effect transistors (MOSFETs)4 owing, for example, to their unique electronic structure and reduced carrier scattering caused by one-dimensional quantum confinement effects1,5. Studies have demonstrated long carrier mean free paths at room temperature in both carbon nanotubes1,6 and Ge/Si core/shell Nanowires7. In the case of carbon nanotube FETs, devices have been fabricated that work close to the ballistic limit8. Applications of high-performance carbon nanotube FETs have been hindered, however, by difficulties in producing uniform semiconducting nanotubes, a factor not limiting Nanowires, which have been prepared with reproducible electronic properties in high yield as required for large-scale integrated systems3,9,10. Yet whether nanowire field-effect transistors (NWFETs) can indeed outperform their planar counterparts is still unclear4. Here we report studies on Ge/Si core/shell nanowire heterostructures configured as FETs using high-κ dielectrics in a top-gate geometry. The clean one-dimensional hole-gas in the Ge/Si nanowire heterostructures7 and enhanced gate coupling with high-κ dielectrics give high-performance FETs values of the scaled transconductance (3.3 mS µm-1) and on-current (2.1 mA µm-1) that are three to four times greater than state-of-the-art MOSFETs and are the highest obtained on NWFETs. Furthermore, comparison of the intrinsic switching delay, τ = CV/I, which represents a key metric for device applications4,11, shows that the performance of Ge/Si NWFETs is comparable to similar length carbon nanotube FETs and substantially exceeds the length-dependent scaling of planar silicon MOSFETs.
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gan nanowire lasers with low lasing thresholds
Applied Physics Letters, 2005Co-Authors: Silvija Gradečak, Hong Kyu Park, Yat Li, Charles M. LieberAbstract:We report optically pumped room-temperature lasing in GaN Nanowires grown by metalorganic chemical vapor deposition (MOCVD). Electron microscopy images reveal that the Nanowires grow along a nonpolar ⟨11-20⟩ direction, have single-crystal structures and triangular cross sections. The Nanowires function as free-standing Fabry–Perot cavities with cavity mode spacings that depend inversely on length. Optical excitation studies demonstrate thresholds for stimulated emission of 22kW∕cm2 that are substantially lower than other previously reported GaN Nanowires. Key contributions to low threshold lasing in these MOCVD GaN nanowire cavities and the development of electrically pumped GaN nanowire lasers are discussed.
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synthetic control of the diameter and length of single crystal semiconductor Nanowires
Journal of Physical Chemistry B, 2001Co-Authors: Mark S Gudiksen, And Jianfang Wang, Charles M. LieberAbstract:A general synthetic method has been developed to control both the diameter and the length of Nanowires during growth. This approach exploits monodisperse nanocluster catalysts to define both the nanowire diameter and the initiation of nanowire elongation during growth by a vapor−liquid−solid mechanism. To demonstrate this new approach, crystalline indium phosphide (InP) Nanowires have been synthesized using a laser catalytic growth (LCG) process combined with gold nanocluster catalysts. InP Nanowires with nearly monodisperse diameters of 10, 20, and 30 nm were grown from nanocluster catalysts having diameters of 10, 20, and 30 nm, respectively. High-resolution transmission electron microscopy studies show that the InP Nanowires prepared in this manner are single crystals with a [111] growth direction. In addition, studies of nanowire growth as a function of growth time have shown that nanowire length is directly proportional to growth time and have enabled the preparation of InP Nanowires with narrow leng...
