Resistance Of Nanowires Research Articles

Individualization and Electrical Characterization of SiGe Nanowires

ABSTRACTSiGe nanowires of different Ge atomic fractions up to 15% were grown and ex-situ n-type doped by diffusion from a solid source in contact with the sample. The phenomenon of dielectrophoresis was used to locate single nanowires between pairs of electrodes in order to carry out electrical measurements. The measured resistance of the as-grown nanowires is very high, but it decreases more than three orders of magnitude upon doping, indicating that the doping procedure used has been effective.

Synthesis of single crystal Sn-doped In2O3 nanowires: size-dependent conductive characteristics

Single crystalline Sn doped In(2)O(3) (ITO) NWs (nanowires) were synthesized via an Au-catalyzed VLS (vapor-liquid-solid) method at 600 °C. The different sizes (~20, ~40, ~80 nm) of the Au NPs (nanoparticles) provided the controllable diameters for ITO NWs during growth. Phase and microstructures confirmed by high-resolution transmission electron microscope images (HRTEM) and X-ray diffraction (XRD) spectra indicated that the phase of In(2)O(3) NWs had a growth direction of [100]. X-ray photoelectron spectroscopy (XPS) was employed to obtain the chemical compositions of the ITO NWs as well as the ratio of Sn/In and oxygen concentrations. The findings indicated that low resistivity was found for ITO NWs with smaller diameters due to higher concentrations of oxygen vacancies and less incorporation of Sn atoms inside the NWs. The resistivity of NWs increases with increasing diameter due to more Sn atoms being incorporated into the NW and their reduction of the amount of oxygen vacancies. Low resistivity NWs could be achieved again due to excess Sn atoms doped into the large diameter NWs. Therefore, by optimizing the well-controlled growth of the NW diameter and interface states, we are able to tune the electrical properties of Sn-doped ITO NWs.

Fabrication of horizontal silicon nanowire arrays on insulator by ion irradiation

We report a simple and potentially mass productive technique to fabricate horizontal single crystalline Si nanowire arrays on insulating substrate based on a self-organized pattern formation mechanism during Xe+ ion beam irradiation of Si-on-insulator material. A periodic ripple surface pattern is created by ion irradiation at 67o incidence angle to the surface normal. The transfer of this pattern to the oxide interface results in an array of electrically disconnected parallel ordered Si nanowires on the insulating oxide. Doping of the nanowires was demonstrated by boron ion implantation and annealing. The morphology and resistivity of the narrow nanowires with large aspect ratio were analysed by cross sectional transmission electron microscopy and scanning spreading resistance microscopy, respectively. Physical reasons of the observed low carrier activation are discussed.

Rectifying characteristics of Te-doped GaAs nanowires

We report on the electrical properties of Te-doped GaAs nanowires (NW) grown via the vapor-liquid-solid mechanism. Gold nanoparticles were used as growth catalysts and contacts for electrical measurements using a nanoprobe technique. Semi-log I-V curves show 6-8 decades of forward-voltage linearity giving an ideality factor of 1.25 ± 0.06 and barrier height of 0.78 ± 0.04 eV. When normalized to NW cross-sectional area, all curves overlapped consistent with an n-type carrier concentration (9 ± 1) × 1017 cm−3 and a constant NW resistivity (2.5 ± 0.5) × 10−3 Ω cm. Raman spectroscopy indicated a small surface depletion width of less than 5 nm.

Negative differential resistance in ZnO nanowires induced by surface state modulation

Negative differential resistance was observed in current–voltage curves of ZnO nanowire embedded sensors in the ethanol environment and conductances at critical points are inversely proportional to the concentration, while this phenomenon was not observed in the toluol environment. Through individual ZnO nanowire experiments, we attribute negative differential resistance to the joint effect of electron transference in the oxidation process of hydroxyls and the nonequilibrium occupation factor for electrons in the process saturating with generation rate of carriers at the ZnO nanowire surface. The inverse variation is associated with the densities of donor and acceptor traps. These results indicate that surface depletion can be beneficial to nanodevices.

High-Frequency Characterization of Contact Resistance and Conductivity of Platinum Nanowires

Contact resistance and conductivity of individual platinum (Pt) nanowires (NWs) embedded in coplanar waveguide structures are investigated at high frequencies. Two approaches to extract the NW conductivity and contact resistance from two-port S-parameters are developed. The first approach is based on transmission-line theory, while the second approach is based on a lumped-element physics-based model. Full-wave and circuit simulations are used to aid validation and the systematic analysis of both methods. Simulations are compared to calibrated on-wafer measurements of individual Pt NWs. The studies of the transmission-line-based approach reveal that the contact resistance can be determined accurately, but the obtained conductivity is inaccurate. By contrast, the lumped-element approach produces accurate results for both the contact resistance and conductivity of Pt NWs. The lumped-element method is used to determine the contact resistance of about 50 Ω and conductivity of 0.013 times the bulk conductivity of Pt for fabricated Pt NWs with 300-nm diameter.

Title: Using Alignment and 2D Network Simulations to Study Charge Transport Through Doped ZnO Nanowire Thin Film Electrodes

AbstractFactors affecting charge transport through ZnO nanowire mat films were studied by aligning ZnO nanowires on substrates and coupling experimental measurements with 2D nanowire network simulations. Gallium doped ZnO nanowires were aligned on thermally oxidized silicon wafer by shearing a nanowire dispersion in ethanol. Sheet resistances of nanowire thin films that had current flowing parallel to nanowire alignment direction were compared to thin films that had current flowing perpendicular to nanowire alignment direction. Perpendicular devices showed ∼5 fold greater sheet resistance than parallel devices supporting the hypothesis that aligning nanowires would increase conductivity of ZnO nanowire electrodes. 2‐D nanowire network simulations of thin films showed that the device sheet resistance was dominated by inter‐wire contact resistance. For a given resistivity of ZnO nanowires, the thin film electrodes would have the lowest possible sheet resistance if the inter‐wire contact resistance was one order of magnitude lower than the single nanowire resistance. Simulations suggest that the conductivity of such thin film devices could be further enhanced by using longer nanowires.

Investigation of conducting nano-structures on ta-C films made by FIB lithography

Tetrahedral amorphous carbon (ta-C) films with high sp3 content were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model was applied to describe the swelling for Ga+ irradiated ta-C films for fluences up to 1×1016cm−2 and was extended to higher fluences using TRIDYN simulations and taken into account sputtering. Van-der-Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290Ωsq−1 was achieved at 1.6×1017cm−2. The resistance of graphitic nano-wires was measured within 109Ω and 107Ω for different irradiation fluences. Irradiations under elevated temperatures show Ga segregation starting at 300°C that promises changes in electrical properties and morphology.

Resolving In Situ Specific‐Contact, Current‐Crowding, and Channel Resistivity in Nanowire Devices: A Case Study with Silver Nanowires

Resistance contributions in a nanowire device are determined accurately. Resistance in silver nanowires, such as conduction-channel and contact resistance, including current-crowding effects, reveal both the true nanowire resistivity and the overall device performance, including dissipation and scaling potential. A comprehensive study on the device layout, the contact geometry and, most importantly, the transfer length over which charge injection between contact electrode and nanowire occurs, is performed.

The Effect of Tetrafluoromethane Plasma Post-Treatment on the Electrical Property of Tungsten Oxide Nanowires

The effects of tetrafluoromethane (CF4) plasma on the surface morphology, chemical compositions, and electrical property of tungsten oxide (W18O49) nanowires are investigated. The nanostructured tungsten oxide nanowires with average length of 250-350 nm were self-catalytically grown on Si substrate. By post-treatment with CF4 plasma for 10 min, the W18O49 nanowires on the substrate showed the highest current response. Longer CF4 plasma post-treatment time demonstrated higher etching effect which demolished the nanowires and resulted in lower conductivity of the samples. The disintegration of the W18O49 nanowires layer after CF4 plasma treatment, revealed physically by the decrease of the average thickness and chemically by the decrease of XRD peak ratio (I 23.0/I 26.0), was closely related to the overall electrical performance. The etching effect was further reveled by Raman spectra showing the evolution of O-W-O and W=O characteristics with the increased post-treatment time. Moreover, the improvement of the electrical property of W18O49 nanowires was elucidated by the exposure rate to explain the mechanism of plasma post treatment in three stages: passivation, degradation and ablation. The maximum exposure rate, corresponding to the maximum conductivity, was achieved by 10 min of CF4 plasma treatment. The time-differentiated exposure analyses confirmed the evolution of resistance of W18O49 nanowires on Si with different post-treatment time which supported the results of surface characterizations.

Extraction of Doping Concentration and Interface State Density in Silicon Nanowires

The disproportionate increase of the resistance of silicon nanowires with reduced diameter is theoretically analyzed, taking into account both the effective conducting cross section and the hole concentration. Previously reported decrease in the conducting cross section and reduction of effective hole concentration that are observed when the nanowire radius is decreased were correlated with an increased influence of the interface state density on the wire's electrical characteristics. By measuring the resistances of doped Si nanowires as a function of nanowire radii and comparing those to an analytical model developed in this study, we extracted both the doping concentration and the interface state density. The measured doping concentration of Si nanowires epitaxially bridged between a pair of doped Si electrodes was found to be 2 × 1018 cm-3 and the corresponding interface trap density is ~ 2 × 1012 cm-2 ·eV-1, which contributes to a reduced ionization of impurities resulting in a lower effective charge hole density than the doping concentration. By measuring the nanowire radius, length, and resistance, this analytic model can be used to estimate, control, and optimize the doping concentration and surface treatment method for Si nanowires for the fabrication of nanowire based devices such as field-effect transistors.

A New Route toward Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions

We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.

Temperature dependent resistivity of platinum–carbon composite nanowires grown by focused ion beam on SiO2/Si substrate

Experimental studies of the temperature dependent resistivity of platinum nanowires grown on an oxidised silicon wafer by using focused ion beam (FIB) have been made. A series of 4-terminal resistivity measurements were carried out in the temperature range 50-300K on single nanowires of width and thickness ~100nm grown by decomposition of an organometallic precursor using Ga^+ ions of different accelerating voltages from 10keV to 30keV. Energy dispersive X-ray spectroscopy showed the nanowires to be composed of more than 60% by volume of carbon, the remainder being principally platinum and gallium. The exact composition depends on the accelerating voltage of the ions used. There is clear evidence from cross-sectional microscopy that the material is a composite consisting of a metallic phase present in the form of nanoscale clusters, randomly distributed in a matrix of carbon. Electrical measurements are consistent with this, showing a critical volume concentration for conduction, which is typical of electron transport in composites with percolating metal phase. Results show an unexpectedly high sensitivity of the temperature dependence of resistivity near the critical volume concentration, which has been explained to arise from thermal strain effects. The anomalous temperature/strain effects observed in this investigation might be exploited in temperature measurement and strain sensor applications.

Structural Dependence of Grain Boundary Resistivity in Copper Nanowires

We report the direct measurement of individual grain boundary (GB) resistances and the critical role of GB structure in the increased resistivity in copper nanowires. By measuring both intra- and inter-grain resistance with a four-probe scanning tunneling microscope, large resistance jumps are revealed owing to successive scattering across high-angle random GBs, while the resistance changes at twin and other coincidence boundaries are negligibly small. The impurity distributions in the nanowires are characterized in correlating to the microstructures. The resistance of high symmetry coincidence GBs and the impurity contributions are then calculated using a first-principle method which confirms that the coincidence GBs have orders of magnitude smaller resistance than the high-angle random GBs.

Acceptor Deactivation in Silicon Nanowires Analyzed by Scanning Spreading Resistance Microscopy

Vertical p-type Si nanowires (NWs) "in-situ" doped during growth or "ex-situ" by B ion implantation are investigated regarding their acceptor activation. Due to the much higher surface to volume ratio of the NW in comparison to bulk material the surface effect plays an important role in determining the doping behaviour. Dopant segregation and fixed positive charges at the Si/SiO2 interface result in an acceptor deactivation. The B concentration introduced into the NW has to balance the deactivation effects in order to reach the intended electrical parameters. Scanning spreading resistance microscopy is used for the electrical characterization of the NWs. This analysis method provides images of the local resistivity of NW cross sections. Resistivity data are converted into acceptor concentration values by calibration. The study demonstrates that scanning spreading resistance microscopy is a suitable analysis method capable to spatially and electrically resolve Si NWs in the nanometer-scale. The NW resistivity is found to be size dependent and shows a significant increase as the NW is below 25 nm in diameter. The obtained data can be explained by a core-shell model with a highly conductive NW core and low conductive shell.

Structural Dependence of Grain Boundary Resistivity in Copper Nanowires

Structural Dependence of Grain Boundary Resistivity in Copper Nanowires

Orientation-Dependent Room-Temperature Ferromagnetism of FeSi Nanowires and Applications in Nonvolatile Memory Devices

Self-catalyzed growth of FeSi nanowires has been achieved via a spontaneous chemical reaction method. The room-temperature ferromagnetism behavior compared to that of bulk FeSi at 4 K is attributed to the enhancement of magnetic coupling behavior correlated to different crystalline orientations. The resistivity of the single-stem FeSi nanowire was determined to be 2650 μΩ·cm. The fabricated memory devices based on FeSi nanowires showed significant C–V hysteresis, exhibiting the memory effect. The strong memory effect can be accounted for by the presence of defects or dangling bonds on the surface of the FeSi nanowires embedded in the SiO2 layer, which enhances the trapping density for nonvolatile memory applications.

Electron–Phonon Interaction and Small Polaron Mechanism of Temperature Dependent Resistivity of Zn Nanowires

Electron–Phonon Interaction and Small Polaron Mechanism of Temperature Dependent Resistivity of Zn Nanowires

Simulation of Joule annealing in nanoscale Pt wires

Joule heating has been observed to cause a reversible change in resistance in gold nanowires followed by a non-reversible change in resistance due to electromigration. Recently, an irreversible change in resistance has been observed to occur in platinum nanowires even before the onset of electromigration. In this work, the platinum nanowire is modeled using a realistic polycrystalline structure with an underlying Ohmic resistor network, the power dissipated through which is taken as the source term for the heat equation. The local solution to the heat equation drives a Monte Carlo Potts annealing with an Arrhenius type energy barrier. The parameters used in this model are taken from known material values and the geometry of the system. The results of this model match quantitatively with the recent experiment and show that annealing due to Joule heating is a material dependent phenomenon.

Remnant magnetoresistance effect at the intersection of two ferromagnetic (Ga,Mn)As nanowires

AbstractCross‐like nanostructures composed of two perpendicular ferromagnetic (Ga,Mn)As nanowires were fabricated using electron‐beam lithography patterning. Nanostructures of different orientations with respect to the crystallographic axes of the parent (Ga,Mn)As epitaxial layer were studied. Electrical resistance of individual nanowires as a function of applied magnetic field were investigated at low temperatures. Low‐field magnetoresistance (MR) of the nanowires exhibits hysteresis‐like behaviour and related remnant resistance in zero magnetic field. These effects are explained in terms of magnetic domain walls (DWs) pinned at the wires intersection, which contribute to the wire resistance. The DW resistivity, which depends on the degree of spin misalignment in the wall, has been determined to be of the order of 1 Ω µm2. High‐field MR has, in turn, allowed determining the lithography‐induced anisotropy field for the nanowires of different crystallographic orientations.