Nonlinear Current-voltage Characteristics Research Articles

Effect of WO<sub>3</sub> Doping on Microstructural and Electrical Properties of ZnO-Pr<sub>6</sub>O<sub>11</sub> Based Varistor Materials

The effect of WO3doping on microstructural and electrical properties of ZnO-Pr6O11based varistor materials was investigated. The doped WO3plays a role of inhibitor in ZnO grain growth, resulting in decreased average grain size from 2.68 to 1.68 μm with increasing doping level of WO3from 0 to 0.5 mol%. When the doping level of WO3was lower than 0.05 mol%, the nonlinear current-voltage characteristics of the obtained varistors could be improved significantly with increasing amount of WO3doped. But when the doping level of WO3became higher, their nonlinear current-voltage performance would be dramatically deteriorated when more WO3was doped. The optimum nonlinear coefficient, varistor voltage, and leakage current of the samples were about 13.71, 710 V/mm and 13 μA/cm2, respectively, when the doping level of WO3was in the range from 0.03 to 0.05 mol%.

Vibration-mediated correlation effects in the transport properties of a benzene molecule

We theoretically analyze correlation effects on the transport properties of a benzene molecule that are mediated by interactions between the motion of the nuclei and the transmitted charge. We focus on the lowest-lying molecular vibrational mode which allows us to derive an analytic expression for the current. The results provide transparent interpretations of various features of the highly nonlinear current-voltage characteristics, which is experimentally accessible through resonant inelastic electron-tunneling spectroscopy.

A novel mode of current switching dependent on activated charge transport

We demonstrate a fully printed transistor with a planar triode geometry, using nanoparticulate silicon as the semiconductor material, which has a unique mode of operation as an electrically controlled two-way (double throw) switch. A signal applied to the base changes the direction of the current from between the collector and base to between the base and emitter. We further show that the switching characteristic results from the activated charge transport in the semiconductor material, and that it is independent of the dominant carrier type in the semiconductor and the nature of the junction between the semiconductor and the three contacts. The same equivalent circuit, and hence similar device characteristics, can be produced using any other material combination with non-linear current-voltage characteristics, such as a suitable combination of semiconducting and conducting materials, such that a Schottky junction is present at all three contacts.

Temperature dependence of the electrical transport properties in few-layer graphene interconnects.

We report a systematic investigation of the temperature dependence of electrical resistance behaviours in tri- and four-layer graphene interconnects. Nonlinear current–voltage characteristics were observed at different temperatures, which are attributed to the heating effect. With the resistance curve derivative analysis method, our experimental results suggest that Coulomb interactions play an essential role in our devices. The room temperature measurements further indicate that the graphene layers exhibit the characteristics of semiconductors mainly due to the Coulomb scattering effects. By combining the Coulomb and short-range scattering theory, we derive an analytical model to explain the temperature dependence of the resistance, which agrees well with the experimental results.

High Schottky barrier at grain boundaries observed in Na1/2Sm1/2Cu3Ti4O12 ceramics

The dielectric properties and nonlinear current–voltage characteristics of Na1/2Sm1/2Cu3Ti4O12 ceramics prepared by a conventional solid state reaction method were investigated. Na1/2Sm1/2Cu3Ti4O12 ceramics exhibited a high dielectric permittivity of 7.0–8.4×103 and low loss tangent (tanδ∼0.030–0.041). Non-Ohmic properties with a high breakdown voltage of ∼2208Vcm−1 and large nonlinear coefficient of 15.6 were observed in Na1/2Sm1/2Cu3Ti4O12 ceramics. Using complex impedance analysis, Na1/2Sm1/2Cu3Ti4O12 ceramics were shown to be electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries. Giant dielectric properties were described based on the electrically heterogeneous microstructure. X-ray photoelectron spectroscopy analysis suggested that the semiconductive nature of grains may be related to the presence of Cu+ and Ti3+. The formation of an electrostatic potential barrier at the grain boundaries of Na1/2Sm1/2Cu3Ti4O12 ceramics was suggested to be caused by the Schottky effect. Interestingly, high electrostatic potential barriers at grain boundaries in Na1/2Sm1/2Cu3Ti4O12 ceramics were calculated and found to be 0.925–0.964eV.

Temperature dependent spin injection properties of the Ni nanodots embedded metallic TiN matrix and p-Si heterojunction

A detailed experimental investigation on magnetic field dependent electronic transport across epitaxial Ni nanoparticles embedded in metallic epitaxial TiN matrix grown on p-type (001) Si substrate heterojunction employing sequential exposure of pulsed excimer laser is reported here. The non-linear current–voltage characteristics along with good rectifying diode like behavior of the junction have been obtained in the range of 100–300K. The ideality factor, reverse saturation current, series resistance and turn-on voltages have been estimated for the heterojunction at different operating temperatures. The dominating current transport mechanism is found to be temperature dependent tunneling assisted Frenkel–Poole type emission. A crossover from negative to positive junction magnetoresistance (JMR) has been observed at ~190K (blocking temperature of the Ni nanodots). The JMR attains a peak with high positive JMR value at 250K, the origin of which has been best explained using standard spin injection theory.

Characterization of electrochemical properties of a micro–nanochannel integrated system using computational impedance spectroscopy (CIS)

The integration of a microchannel with an ion-selective nanochannel exhibits nonlinear current–voltage characteristics owing to the concentration polarization effects. In this paper, an efficient computational impedance spectroscopic technique (CIS) is developed using an area averaged multi-ion transport model (AAM). Using this technique, we investigate the ion transport dynamics in the Ohmic and non-Ohmic regions. Under no external DC bias and in the Ohmic regime, we observe two distinct arcs. The low frequency diffusional arc characterizes the diffusion-transport and the electrical double layer (EDL) charging effects at the interface of the micro–nanochannel, while the high frequency geometric arc characterizes the electric migration and displacement current effects inside the nanochannel and in the microchannel. Further, we observe an anomalous inductive arc at low frequencies (fLm2/D≤1), in the overlimiting regime. This arc is primarily attributed to the phase effects between the first harmonic contribution of the total ionic concentration and the electric field in the induced space charge region. The microscopic diffusion boundary layer (DBL) lengths observed in the microchannel are also efficiently characterized from the impedance spectrum. Equivalent circuit models are designed to interpret the impedance response.

Figurate superlattices in the classical problem of signal filtering against the noise background on the basis of a cellular nonlinear network

A new type of multilayer semiconductor structures (figurate superlattices) that can be used in con� struction of resonanttunneling diode components ha s been proposed and investigated. The superlattice advantages over structures with standard nonlinear current-voltage characteristics are discussed as applied to the classical filtering problem on the basis of a cellular nonlinear network. It is demonstrated that the abso� lutely new, socalled fractal cellular nonlinear networks can be developed.

Interaction effects in electric transport through self-assembled molecular monolayers

We theoretically investigate the effect of inter-molecular Coulomb interactions on transport through molecular monolayers (or other devices based on a large number of nanoscale conductors connected in parallel). Due to the interactions, the current through different molecules become correlated, resulting in distinct features in the non-linear current-voltage characteristics, as we show by deriving and solving a type of modified master equation, suitable for describing transport through an infinite number of interacting conductors. Furthermore, if some of the molecules fail to bond to both electrodes, charge traps can be induced at high voltages and block transport through neighboring molecules, resulting in negative differential resistance.

Carrier Density and Electric Field Dependent Nonlinear Transport of Chemical Vapor Deposition Graphene

We report on the measurements of nonlinear current-voltage characteristics of graphene fabricated by chemical vapor deposition. The current-voltage characteristic is described by a power law with a superlinear dependence of the current on the voltage, and the nonlinearity depends on the carrier density and the excitation level. The nonlinearity is strongest at the Dirac point and becomes weaker as the carrier density increases. At the Dirac point, we also observe a crossover to a much stronger nonlinear transport when the electric field increases above 104 V/m.

Novel polymeric composites with nonlinear current-voltage characteristic

Results of study of novel polymeric composites with nonlinear current-voltage characteristic are represented in this paper. Linear low-density polyethylene and polyvinylidene fluoride were used as polymeric matrices. Powder of silicon carbide was used as nonlinear filler. The study of main properties of composites with nonlinear current-voltage characteristic is carried out by two methods such as measurement of current-voltage characteristics and dielectric spectroscopy in frequency domain. Both a nonlinearity coefficient of current-voltage characteristic and threshold value of electric field strength at which nonlinear growth of a current occurs have been evaluated.

A New Sliding Mode Controller for DC/DC Converters in Photovoltaic Systems

DC/DC converters are widely used in many industrial and electrical systems. As DC/DC converters are nonlinear and time-variant systems, the application of linear control techniques for the control of these converters is not suitable. In this paper, a new sliding mode controller is proposed as the indirect control method and compared to a simple direct control method in order to control a buck converter in photovoltaic applications. The solar arrays are dependent power sources with nonlinear voltage-current characteristics under different environmental conditions (insolation and temperature). From this point of view, the DC/DC converter is particularly suitable for the application of the sliding mode control in photovoltaic application, because of its controllable states. Simulations are performed in Matlab/Simulink software. The simulation results are presented for a step change in reference voltage and input voltage as well as step load variations. The simulations results of proposed method are compared with the conventional PID controller. The results show the good performance of the proposed sliding mode controller. The proposed method can be used for the other DC/DC converter.

MOCVD-grown heterostructures with GaAs/AlGaAs Superlattices: Growth features and optical and transport characteristics

The results of studies of MOCVD growth regularities of GaAs/AlGaAs superlattices with narrow forbidden minibands are presented. The spectra of photoluminescence and X-ray diffraction are measured, the concentration distribution profiles of components are determined by secondary-ion mass spectrometry, and the concentration distribution of charge carriers are determined by the method of capacitance profiling. The relation of the growth modes of heterostructures to their crystalline characteristics and luminescent and electrical properties are studied. The photoluminescence measurements indicate the high quality of the superlattices. X-ray diffraction and the data on secondary ions confirm the high periodicity of the superlattices grown in the optimized modes. The nonlinear current-voltage characteristics with a region of negative differential conductivity at moderate voltages and subsequent current increase at higher voltages because of tunneling between the minibands is found for the superlattices grown in the optimal growth modes. Current oscillations at frequencies of ∼60 MHz were observed in the region of negative differential conductivity. The negative differential conductivity and oscillations confirm the presence of the electron localization effect in moderate electric fields in the first conductivity miniband, which emerges due to the Bragg reflection of carriers in the superlattice.

Graphene/polypyrrole nanofiber nanocomposite as electrode material for electrochemical supercapacitor

The present work explores a facile route to synthesize nanocomposite based on graphene and Polypyrrole nanofiber using a biopolymer, sodium alginate. The synthesis procedure of composite is simple, inexpensive and ecofriendly. The possible interaction between graphene and PPy nanofiber has been characterized by FTIR analysis. Morphological study confirmed the fiber like morphology of PPy and the presence of graphene in the nanocomposite. The composite achieved high electrical conductivity of 1.45 S/cm at room temperature and also showed nonlinear Current–Voltage characteristics, which indicates it's potential to be used in various device applications. A maximum capacitance value of 466 F/g has been obtained for this composite at 10 mV/s scan rate in 1 M KCl solution. The composite also showed highest energy density of 165.7 Wh/Kg at 10 mV/s scan rate. Noticeable improvements in other electrochemical properties allow its possible application as electrode material for Supercapacitors.

Nonlinear current-voltage characteristics of conductive polyethylene composites with carbon black filled pet microfibrils

Current-voltage electrical behavior of in situ microfibrillar carbon black (CB)/poly(ethylene terephthalate) (PET)/polyethylene (PE) (m-CB/PET/PE) composites with various CB concentrations at ambient temperatures was studied under a direct-current electric field. The current-voltage (I-V) curves exhibited nonlinearity beyond a critical value of voltage. The dynamic random resistor network (DRRN) model was adopted to semi-qualitatively explain the nonlinear conduction behavior of m-CB/PET/PE composites. Macroscopic nonlinearity originated from the interfacial interactions between CB/PET micro fibrils and additional conduction channels. Combined with the special conductive networks, an illustration was proposed to interpret the nonlinear I-V characteristics by a field emission or tunneling mechanism between CB particles in the CB/PET microfibers intersections.

Conduction in nanostructured La1−x Sr x FeO3 (0 ≤ x ≤ 1)

We investigated electrical properties of nanostructured La1−x Sr x FeO3 (0 ≤ x ≤ 1) from 300 K–400 K. The nanostructured La1−x Sr x FeO3 (0 ≤ x ≤ 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO3 with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ≤ 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO3 from 300 K–400 K. The experimental values of field-lowering coefficient were by 2.56–6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe4+ ions in addition to Fe3+ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La1−x Sr x FeO3 (0 ≤ x ≤ 1) was also carried out in the temperature range from 300 K–400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La0.9Sr0.1FeO3.

Enhanced Raman scattering and nonlinear conductivity in Ag-doped hollow ZnO microspheres

Hollow spherical ZnO particles doped with Ag were synthesized with a two-step oxidation and sublimation furnace annealing process. Ag nanoparticle precipitates, as observed by transmission electron microscopy, were present in the polycrystalline ZnO matrix at Ag concentrations below 0.02 mol%, significantly below the 0.8 mol% solubility limit for Ag in ZnO. Enhanced Raman scattering of ZnO phonon modes is observed, increasing with Ag nanoparticle concentration. A further enhancement in Raman scattering due to resonance effects was observed for LO phonons excited by 2.33-eV photons as compared with Raman scattering under 1.96-eV excitation. Room-temperature photoluminescence spectra showed both a near-band-edge emission due to free exciton transitions and a mid-gap transition due to the presence of singly ionized oxygen vacancies. ZnO:Ag particles were measured electrically in a packed column and in monolithic form, and in both cases displayed nonlinear current–voltage characteristics similar to those previously observed in sintered ZnO:Ag monoliths where Ag-enhanced disorder at grain boundaries is thought to control current transport. We demonstrate therefore that Ag simultaneously modifies the electrical and optical properties of ZnO particles through the introduction of vacancies and other defects.

Electrical properties of new tin dioxide varistor ceramics at high currents

New dense SnO 2 -based varistor ceramics with high nonlinear current–voltage characteristics (nonlinearity coefficients are of approximately 50) in a system of SnO 2 –CoO–Nb 2 O 5 –Cr 2 O 3 –Y 2 O 3 –SrO–MgO are reported. The current–voltage behaviour at high currents is studied by using exponential voltage pulses. The obtained SnO 2 varistor ceramics exhibit low grain resistivity values of 0.23–0.64 ohm cm. To date, such values are the lowest known for SnO 2 varistors, and are closely approaching the grain resistivity of the ZnO varistor. The current–voltage characteristics of the obtained SnO 2 -based varistor materials are reproducible in a wide current range from 10 −11 to approximately 10 4 A cm −2 . The minimum current density and the minimum electric field necessary to cause the irreversible electrical breakdown are measured. It is established that a decrease in the grain resistivity leads to an increase in the minimum current density necessary for irreversible electrical breakdown to occur.

Electron transport in discontinuous gold films and the effect of Coulomb blockade and percolation

Understanding the electron transport in disordered assemblies of weakly coupled nano-sized metal clusters is important for many applications. Here, we investigate experimentally and theoretically the electron transport properties of metal cluster assemblies in the form of discontinuous gold films. Discontinuous films of different average island size are produced by sputter deposition, and the resistance and the non-linear current-voltage (I-V) characteristics of the films are measured as a function of temperature. To interpret the experimental electron transport data, a conduction percolation model is employed where broad probability distributions for both the tunnel junction gaps and the Coulomb blockade energies are used. Excellent agreement between experimental data and model calculations is found. In particular, the non-Arrhenius resistive behavior, the I-V power-law behavior, and the I-V characteristics at large bias voltage are all shown to be due to a conduction percolation mechanism governing disordered networks of nano-sized metal islands connected by tunnel junctions.

Understanding anomalous current–voltage characteristics in microchannel–nanochannel interconnect devices

The integration of a microchannel with a nanochannel is known to exhibit anomalous nonlinear current–voltage characteristics. In this paper, we perform detailed numerical simulations considering a 2-D nonlinear ion transport model, to capture and explain the underlying physics behind the limiting resistance and the overlimiting current regions, observed predominantly in a highly ion-selective nanochannel. We attribute the overlimiting current characteristics to the redistribution of the space charges resulting in an anomalous enhancement in the ionic concentration of the electrolyte in the induced space charge region, beyond a critical voltage. The overlimiting current with constant conductivity is predicted even without considering the effects of fluidic nonlinearities. We extend our study and report anomalous rectification effects, resulting in an enhancement of current in the non-ohmic region, under the application of combined AC and DC electric fields. The necessary criteria to observe these enhancements and some useful scaling relations are discussed.