Anomalous Current-voltage Characteristics Research Articles

Anomalous current-voltage characteristics of SFIFS Josephson junctions with weak ferromagnetic interlayers.

We present a quantitative study of the current–voltage characteristics (CVC) of SFIFS Josephson junctions (S = bulk superconductor, F = metallic ferromagnet, I = insulating barrier) with weak ferromagnetic interlayers in the diffusive limit. The problem is solved in the framework of the nonlinear Usadel equations. We consider the case of a strong tunnel barrier such that the left SF and the right FS bilayers are decoupled. We calculate the density of states (DOS) in SF bilayers using a self-consistent numerical method. Then we obtain the CVC of corresponding SFIFS junctions, and discuss their properties for different set of parameters including the thicknesses of ferromagnetic layers, the exchange field, and the magnetic scattering time. We observe an anomalous nonmonotonic CVC in case of weak ferromagnetic interlayers, which we attribute to DOS energy dependencies in the case of small exchange fields in the F layers.

Imbalanced charge carrier mobility and Schottky junction induced anomalous current-voltage characteristics of excitonic PbS colloidal quantum dot solar cells

Anomalous current-voltage (I-V) characteristics, as reported with increasing frequency, can significantly compromise the energy conversion efficiency of colloidal quantum dot (CQD) solar cells. This paper applied a purely hopping transport model rather than the traditional Schottky-diode equation to interpret the anomalous I-V curves measured in CQD solar cells with a structure: ITO/ZnO/PbS-TBAI QD/PbS-EDT QD/Au. Anomalous I-V curves were found at temperatures below 300K. A double-diode-equivalent electric circuit was developed for the quantitative analysis of these anomalous I-V curves, yielding multiple hopping transport parameters, such as hopping diffusivity, diffusion length, mobility, and lifetime. Quantitative analysis revealed that the imbalanced charge carrier mobility in the carrier transport (PbS-TBAI) and extraction (PbS-EDT) layers, as well as the existence of a reverse Schottky diode at the PbS-EDT/Au interface, played key roles in the formation of the anomalous I-V curves. Furthermore, charge-transfer (CT) states, located at the ZnO/PbS-TBAI interface, were found to reduce the CQD solar cell open-circuit voltage through radiative and non-radiative recombination of excitons. A modified Einstein equation was also validated, further proving the presence of a Schottky barrier and pointing to a rate determining interface for the I-V behaviors of our solar cells.

Negative differential resistance in nanoclay films offers pressure sensing characteristics

Thin fluid films of discotic nanoclay particles dispersed in water were observed to exhibit anomalous current-voltage (I-V) characteristics at room temperature. The I-V characteristics exhibit a transition from space charge limited conduction to negative differential resistance on crossing a certain bias of 20 V. Here, the maximum current (Imax) found to be around 20 μA and Imax was found to scale with applied pressure (P) following empirical relation Imax ∼ P1/4 indicating that these films can be used as pressure sensors.

(Invited) Anomalous Current-Voltage Characteristics and Non-Adiabatic/Adiabatic Phase Transitions in Ultra-Clean Suspended Carbon Nanotubes

not Available.

Transport Properties in a Single Domain of Microscale Sr2RuO4 Single Crystals

We report our approach to measuring the transport properties in a single chiral order parameter domain of microscale Sr2RuO4 single crystals. Sr2RuO4 single crystals were grown by the solid-phase reaction. Microscale single crystals were deposited from a dispersed liquid, and selected from the result of the chemical composition and crystallinity of the dispersed crystals. The selected crystals attached to gold electrodes show superconducting properties. We also found the anomalous current–voltage characteristics that show that induced voltage is an even function of bias current.

Anomalous current–voltage characteristics and structural phenomena in an Au–Si interface

We report an abnormal current–voltage ( I–V ) characteristic observed on an Au–Si interface fabricated by a unique focused ion beam sputtering microdeposition method. The Au–Si interface shows neither Schottky nor ohmic behavior, but the I–V curve has a d I /d V peak at zero voltage. High-resolution transmission electron microscopy studies reveal the existence and unstable nature of an ∼10 nm thick interfacial layer at the Au–Si contact. The unusual electrical behavior is likely correlated with this metastable interfacial layer.

Anomalous current–voltage characteristics and colossal electroresistance of amorphous carbon film on Si substrate

Amorphous carbon film (a-C film) was deposited on n-Si substrate by pulsed-laser deposition at room temperature. The electrical transport properties of a-C film/n-Si were investigated by current–voltage (I–V) measurements at various temperatures. The results indicate that the resistance of a-C film/n-Si is controlled by the applied electric current. The most important result is that when the value of the electric voltage is larger than a threshold, the current increases abruptly to a very large value, and the value of the voltage threshold decreases with increasing temperature. Correspondingly, the colossal electroresistance (ER) was achieved in the temperature range measured. The ER reaches −84.5% and −99.5% at T=310K and 170K, respectively. The mechanism of the I–V characteristics may be understood by an energy band structure of a-C film/n-Si. The anomalous I–V characteristics and colossal ER should be of interest for various applications such as field-effect devices.

Anomalous current–voltage characteristics of InGaN/GaN light-emitting diodes depending on Mg flow rate during p-GaN growth

The dependence of the forward operating voltage of In1−xGaxN/GaN light-emitting diodes (LEDs) on Mg flow rate during the growth of the p-GaN layer has been investigated. The hole concentration in the p-GaN layer increases with Mg flow rate up to a critical value and gradually decreases for higher flow rates. We find that the forward threshold voltage of the LEDs mainly depends on the Mg concentration in the p-GaN layer and is rather independent of hole concentration. A current flow mechanism involving the impurity acceptor band, instead of the usual valence band, is proposed to elucidate this anomalous behaviour of the I–V characteristics.

Anomalous current–voltage characteristics of thin polymer films

In this paper we have investigated organic light emitting diodes with such electroluminescent materials as aromatic polyimide, poly∼N-vinylcarbazole (PVK) and dye doped PVK. N-type current–voltage characteristics with negative differential resistance for the thin polymeric and organic films are analyzed. No reasonable explanation has been provided for this phenomenon until now. Here we suggest that a polymer(organic)/metal interface containing various inhomogeneities and metal spikes is responsible for this effect. We detect also the black-body radiation, whose temperature exceeds both the melting point and the sublimation temperature of the metal of the electrode. We suppose that the current density through the spike in any cases is large enough to cause the explosion of the tip of the spike and the detected radiation has the hot plasma origin. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Anomalous current-voltage characteristics of polymer light-emitting diodes

Light-emitting diodes based on an alternating copolymer containing triphenylamine and phenylene units (TPA-PPA) were prepared, and electrically and optically characterized. The diode with a structure of indium tin oxide/TPA-PPV/Al exhibited a ``current anomaly'' phenomenon. We demonstrated that the ``current anomaly'' is caused by a reverse internal electric field owing to the reabsorption of electroluminescent light rather than the changes in the aluminum-doping concentration during operation.

Synthesis and electroluminescence properties of a novel poly(paraphenylene vinylene)‐based copolymer with tri(ethylene oxide) segments on the backbone

AbstractA novel light‐emitting copolymer [tri(ethylene oxide)–poly(paraphenylene vinylene) (TEO–PPV)] containing alternating rigid, conjugated distyrylbenzene [poly(paraphenylene vinylene) model oligomer] as light‐emitting units and flexible tri(ethylene oxide) as ionic conductive units was synthesized. The polymer was characterized with Fourier transform infrared, 1H‐NMR, ultraviolet–visible spectroscopy, differential scanning calorimetry, and gel permeation chromatography. TEO–PPV has excellent solubility in conventional organic solvents such as tetrahydrofuran, chloroform, benzene, and toluene. The estimated lowest unoccupied molecular orbital, highest occupied molecular orbital, and band gap are 2.35, 5.29, and 2.94 eV, respectively. Single‐layer and double‐layer light‐emitting diodes with indium tin oxide anodes and calcium cathodes were fabricated, and the photoluminescence (PL) and electroluminescence (EL) properties were investigated. The maximum EL emissive peak (475 nm) of the devices is essentially the same as that of PL. Anomalous current–voltage characteristics were observed in both devices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2195–2200, 2002

A systematic study of MOCVD grown InP/InGaAIAs heterojunction bipolar transistors with anomalous switching behavior

A new S-shaped switch based on the InP/InGaAlAs material system has been successfully fabricated and demonstrated. Due to the avalanche multiplication and potential redistribution process, the interesting multiple-negative-differential-resistance (MNDR) is found under the inverted operation mode at room temperature. The three-terminal NDR characteristics are investigated under the applied base current I B . Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics at 77K are also observed. The switching behaviors demonstrate that the proposed structure is a good candidate for multiple-valued logic applications.

Analysis of anomalous current–voltage characteristics of silicon solar cells

The current–voltage characteristics of solar cells, under illumination and in the dark, represent a very important tool for characterizing the performance of the solar cell. The PC-1D computer program has been used to analyze the deviation of the dark current–voltage characteristics of p–n junction silicon solar cells from the ideal two-diode model behavior of the cell, namely the appearance of “humps” in the I– V characteristics. The effects of the surface recombination velocity, the minority-carrier lifetimes in the base — and emitter regions of the solar cell, as well as the temperature dependence of the I– V characteristics have been modeled using PC-1D. It is shown that the “humps” in the I– V characteristics arise as a result of recombination within the space-charge region of the solar cell, occurring when conditions for recombination are different from the simple assumptions of the Sah–Noyce–Shockley theory.

Multiple-route and multiple-state current-voltage characteristics of an InP/AlInGaAs switch for multiple-valued logic applications

A novel multiple-state switching device based on an InP/AlInGaAs heterojunction bipolar transistor (HBT) structure has been successfully fabricated and demonstrated. The common-emitter current gain up to 25 is obtained under the forward operation mode. However, the anomalous multiple-negative-differential-resistance (MNDR) phenomena controlled either by electrical or optical input signals are observed under the inverted operation mode. The studied device exhibits a single-route S-shaped NDR behavior in the dark and a distinct significant S-shaped MNDR phenomena by introducing an incident light source at room temperature. Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics are also observed at 77 K. The switching behaviors are attributed to the avalanche multiplication, barrier lowering effect and potential redistribution process. Experimental results show that the studied device provides a good potentiality for multiple-valued logic and optoelectronic switching system applications.

Anomalous current-voltage characteristics in organic light-emitting devices

Quasi-reversible current maxima at low voltage, leading to N-type current-voltage characteristics with negative differential resistance, have been observed in different types of organic light-emitting devices including conjugated polymer LEDs, dye-doped polymeric LEDs and LEDs from evaporated small molecules. We have investigated the dependence of this phenomenon on different external parameters, like layer thickness, temperature and time. We found that the usual explanations, e.g. by tunneling, cannot satisfactory explain our observations. Instead, our experiments indicate that spatially local effects are responsible for the anomalous high current flow at low voltage. The implications for device operation and lifetime are discussed.

Electric characteristics of contact junctions between NbTi multifilamentary wires

Anomalous current-voltage characteristics have been found for a mechanical contact junction between NbTi superconducting multifilamentary wires. The pressure contact junctions between superconductors were created by either parallel-conductor contact or crossed-conductor contact. The junctions are superconductive over a limited current range. The current-voltage characteristics show switching phenomena, that are both large and very fast, at transitions between zero voltage and resistive states. The switching time is about 2 /spl mu/s. A zero-voltage current of about 60 A was obtained for a 75-mm-long junction at zero applied magnetic field. The current-voltage curve of the junction shows hysteresis that varies with the contact junction's structure. It has been confirmed that mechanical pressure contact junctions can be used as persistent switches without heaters. Additionally, contact junctions may provide uniform current distribution for multistrand cables.

Anomalous current-voltage characteristics along the c-axis in YBaCuO thin films prepared by MOCVD and AFM lithography

We have proposed a fabrication process of intrinsic Josephson junctions (IJJs) using AFM lithography and successfully obtained IJJs in YBaCuO thin films deposited by MOCVD. A sample shows clear hysteresis and 23 voltage steps related to IJJs in the I- V curve. The maximum width of a step is about 2 mV at 5 K. We discuss the I– V characteristics and estimate the order of the parameters for the IJJ.

Modeling of anomalous current-voltage characteristics in floating body fully depleted SOI nMOSFETs

An analytic model is derived for predicting the anomalous I D− V GfS and I D− V DS characteristics in a floating body fully depleted silicon-on-insulator (SOI) nMOSFETs with parasitic bipolar junction transistor (BJT). All current components in the MOSFET as well as the parasitic BJT are considered in this model. It shows that the single-transistor latch in the I D− V GfS characteristics is due to multistable floating body potentials. The study also reveals that the breakdown and latch phenomena are strongly dependent on the parasitic bipolar current gain and multiplication factor. The effective mobility variation and short channel effects are included in this model. Furthermore parametric dependences, such as SOI film thickness and body doping concentration, are examined to alleviate the latch effect and give the physical insight for optimal design. Results obtained from this model are in good agreement with the measured I D− V GfS and I D− V DS characteristics.

Anomalous electrical characteristics, memory phenomena and microcavity effects in polymeric light-emitting diodes

The electrical and emission properties of poly( p-phenylene vinylene) -based light-emitting devices with different thicknesses of the emitting layer, and especially the influence of the ambient atmosphere, were examined. In vacuum anomalous current-voltage characteristics and a memory switching phenomenon were found in single-layer sandwich structures (ITO/polymer/Al, Au/polymer/Al). In air the anomalous behaviour disappeared. Microcavity effects in the electroluminescence emission of the single-layer devices are further reported.

Observation of the anomalous current–voltage characteristics of GaAs/n+-InGaAs/GaAs doped-channel structure

A GaAs/n+-In0.2Ga0.8As/GaAs doped-channel field-effect transistor structure has been fabricated and studied. A typical transistor performance with a threshold voltage of about −3.0 V and transconductance of up to 160 mS/mm is obtained in the lower gate-source voltage (VGS <−1.0 V) regime. However, for some devices, the three-terminal-controlled N-shaped negative-differential-resistance (NDR) behavior is observed at the saturation regime of current–voltage characteristics under higher gate-source bias (VGS≥−1.0 V) condition. The interesting NDR phenomenon is believed to be attributed to the real-space transfer and deep-level electron trapping effect.