Experimental Current-voltage Curves Research Articles

Approach to chemical equilibrium of water dissociation for modeling bipolar membranes in acid-base flow batteries

Understanding the behavior of bipolar membranes under forward and reverse bias in multi-ion solutions is essential for their application in acid-base flow batteries (ABFB). To this end, a two-dimensional steady-state model of the bipolar membrane is proposed based on the Nernst-Plank and Poisson equations coupled with water dissociation and acid-base neutralization reactions. The second Wien effect and catalytic activity are included in the water dissociation rate model at the bipolar junction. Experimental current-voltage curves were obtained using linear sweep voltammetry to validate the model. A commercial bipolar membrane was used in NaCl solutions at 0.25 and 0.5 mol L−1 concentrations, a mixture of NaCl-HCl and NaCl-NaOH solutions at different concentrations, and solutions of HCl and NaOH at 0.5 mol L−1 concentration. The catalytic activity coefficient was the only model parameter fitted to the experimental data; all other properties and parameters were obtained from the literature or calculated from the membrane supplier data. The numerical solution of the bipolar membrane model complements the experimental results. It shows a full view of conductivity, ion concentration, and potentials across the bipolar membrane as a function of its polarization.

Effect of Biased Field Rings to Improve Charge Removal after Heavy-Ion Strikes in Vertical Geometry β-Ga2O3 Rectifiers

In this study, the response to a heavy-ion strike and the resulting single effect burnout on beta-Ga2O3 Schottky diodes with biased field rings is investigated via TCAD. The model used to simulate the device under high-reverse bias is validated using experimental current-voltage (I-V) curves. A field ring configuration for the device demonstrates an improved charge removal after simulated heavy-ion strikes. If the time scale for charge removal is faster than single event burnout, this can be an effective mechanism for reducing the effect of single ion strikes. This study explores various configurations of the termination structure and shows the impact of different design parameters in terms of a transient response after the ion strike.

Molecular Dipole-Modulated Charge Transport across Organic Monolayer-Modified Metal–Semiconductor Junctions

The effect of molecular dipoles on charge transport across organic monolayer-modified metal–semiconductor junctions has been investigated systematically. We have prepared a new set of organic monolayers with varied terminal derivatization on crystalline silicon to construct molecular junctions using mercury drops as the top contact electrode. Although the surface and structural characterization indicated the high quality and uniformity of all these monolayers, the junctions (Hg/R–Si≡) showed a diverse electrical performance. Beyond taking the most common theoretical approach to analyze these molecular junctions, that is, applying the thermionic emission model (TE) to calculate the barrier height (ΦB) and ideality factor (η), we have examined the contribution of the carrier generation–recombination (CGR) mechanism by fitting the experimental current–voltage curves. When η is close to unity, the charge transport across these molecular junctions is dominated by TE; for η values greater than unity, TE indeed remains the dominant current transport pathway, while CGR transport becomes significant.

Conduction in materials and devices: A universal expression for transport

The space-charge-limited-current spectroscopy is a consolidated technique for studying electrical properties of materials and devices. In general, the conduction in the material can be expressed as a single scaling law, relating the current with voltage and gap (or sample thickness) with different values for the exponents. However, some aspects of this technique remain obscure, especially when dealing with very thin (few nanometer) gaps and solids. Beyond this, abrupt transitions between different transport regimes are observed, whereas unusual space-charge-limited current behaviors are expected in out of 2D plane of 2D-material-based heterostructures. Therefore, there is a need for a universal model to describe the current–voltage characteristic curves, including different conduction mechanisms as well as smooth transitions between them. This goal, pursued for decades without substantial success, is not achievable based on the mentioned simple scaling laws, requiring a new approach. In this work, we propose a universal model with the same underlying physics. A new function is considered which contains relevant information for transport and accounts for most of the fingerprints observed in experimental current–voltage curves of the most diverse set of physical systems, from materials to devices. This approach leads to the usual scaling laws for constant values of the transport function, whereas it is abandoned for the trap filling regime, although the same familiar higher slopes of current–voltage curves can be recovered. The model is used to fit the experimental curves of the most diverse materials and devices in order to show its applicability and accuracy.

Modeling the electrical characteristic of InGaN/GaN blue-violet LED structure under electrical stress

The role of deep defects and their physical origin in InGaN/GaN LED are still widely investigated and debated, in particular their impact on the electrical and optical characteristics and on the reliability of the device. In this paper we evaluate the electrical and optical behavior of a single quantum well InGaN/GaN 420 nm LED during a medium-term accelerated ageing test. From these measurements, an increase in the sub-turn on current was observed: this process was ascribed to the stress-induced generation of defects in proximity of the active region and thus related to an increase of the correlated trap assisted tunneling. Subsequently we modelled the device electrical characteristics, evidencing the fundamental role of deep defects in determining the shape of the I-V curve in low forward bias. We reproduced with high accuracy the experimental current-voltage curves acquired during the ageing test, demonstrating that the increase in forward leakage can be entirely ascribed to the increase in concentration of a sole defect deep level located near midgap. These results provide a better understanding about the defect formation mechanism, that can be used to model and understand the behavior of the devices during ageing.

Obtention of solar cell parameters, through convergence of iterative cycles. Part 2: Application to experimental current-voltage measurements

In this Part 2 of this series of articles, the application of the iterative cycles CycleA and CycleB proposed in Part 1, to determine the solar cell parameters (the shunt resistance (Rsh), the series resistance (Rs), the ideality factor (n), the light current (Ilig), and the saturation current (Isat)) on experimental current voltage (IV) and current density (JV) curves, is given. Several number of measured points per voltage (PV) are attempted, from approximately PV=1measuredpointsV to PV=52measuredpointsV. In one case, the application of the iterative cycles to IV curves showing the roll-over effect is discussed, while in another case, their application to solar panels is analysed, revealing that the iterative cycles can also be used in the case of solar panels, and not only for laboratory-made solar cells, in voltage ranges larger than [0 V,1 V]. Also, cases in darkness and under illumination are evaluated. In most cases, reasonable values are obtained for Rsh, Rs, n,Isat and Ilig, which simulated properly the IV or JV curves.

Realization and real application of two prototypes for photovoltaic panel data acquisition

This paper presents a comparative study of two low-cost prototypes for photovoltaic (PV) panel characterization and data acquisition. The first prototype is based on classical current and voltage sensors. However, the second new proposed prototype is based on low-cost components for measuring PV current and voltage. A typical T9C-M20-36 photovoltaic panel has been chosen for experimental tests and simulation in Proteus Isis and MATLAB/Simulink software’s. This panel provides, under standard test conditions (STC), a maximum power of 20 W under an optimal current of 1.2 A and an optimal voltage of 18 V. The proposed circuits were first simulated under Proteus Isis software and implemented in low-cost Arduino Uno board. Using PLX-DAQ interface, users can check in real time the evolution of recorded data such as irradiation level, PV panel temperature, voltage, current and power. Experimental results show that the new realized prototype perform well than the classical circuit. The validation of the new proposed circuit is performed by comparison between experimental current–voltage curves obtained by the two conceived circuits and the theoretical current–voltage characteristic. This last curve is reproduced accurately by simulation in MATLAB/Simulink environment using the remarkable three points (RTP) provided in the PV panel datasheet. The obtained results show that the theoretical current–voltage curve agree very well with the experimental PV data recorded by the new prototype compared to data resulting by the classical circuit. Therefore, the new low-cost circuit of PV measurement and data acquisition could be an efficient tool for PV characterization and can be considered in many other applications such as diagnostic default algorithm.

Extraction of interface trap density by analyzing organohalide perovskite and metal contacts using device simulation

We estimated the interface trap density by examining methylamine-lead-iodide (MALI, CH3NH3PbI3) and metal contacts. We analyzed experimental current-voltage curves from two MALI-based resistive memory devices, which are Au/MALI/indium-tin-oxide and Ag/MALI/Pt, using a device simulator. We obtained effective work functions (EWFs) for MALI/metal contacts by considering Fermi level pinning attributed to the interface states comprising metal-induced gap states (MIGSs) and interface traps. Through our theoretical consideration, we concluded that the interface trap density is about 1015 eV−1 cm−2 at MALI/metal contacts because the low MIGS density of about 1013 eV−1 cm−2 obtained from a theoretical equation makes little contribution to the interface state density of 1015 eV−1 cm−2 obtained from the linear fitting between the metal work functions and the EWFs.

Model and numerical experiment for calculating the theoretical current-voltage characteristic in electro-membrane systems

This work is devoted to problems of numerical calculation of the theoretical current-voltage characteristics (CVC) and galvanography of electromembrane systems in the potentiometric mode. The purpose of this work is the derivation of the formula for calculating the CVC and galvanography of electromembrane systems in the potentiometric mode, which allows calculating stable relative to random errors and rounding errors in over-limiting current densities. To use the formulas, it is necessary to create a mathematical model for calculating the local current density. In this paper, as this model model is used transport of ions in binary salt in the desalination channel, taking into account electroconvection. The electromembrane systems have been used for water medium preparing in mobile mini systems for generating heat and electrical energy as well as vapour producing. The quality of clean water influences on reliability and life time of these systems, including vapour generator and dam-vapour turbine. The obtained formula in the form of a double integral of the local current density is derived, which allows calculating them steadily with respect to random errors and rounding errors. The formulas allowing considering CVC stably with respect to random errors and rounding errors are obtained, and the physical meaning of these formulas is clarified. The calculation of the theoretical CVC with the use of a mathematical model of ion transfer binary salts given electroconvection and shows that it qualitatively coincides with the experimental current-voltage curves. The quantitative difference can be explained by the fact that the mathematical model does not take into account the reaction of water dissociation / recombination, gravitational convection and other transport mechanisms.

(Invited) Evolutionary Parameter Extraction for Organic TFT Compact Models Including Contact Effects

The development of accurate and computationally efficient models is critical to reduce the cycle time between design, manufacturing and characterization of electronic devices, circuits and systems. The models must include degrading effects in order to better describe the performance of manufactured device. This is the case of contact effects in the modelling of organic thin film transistors (OTFTs). In fact, much effort was made to include contact effects into compact models. In this work, we consider a generic analytical model for the current-voltage (ID-VD) characteristics of OTFTs, valid for all the operation regions of the transistor, including the subthreshold region [1]. This model was later redefined with the inclusion of a model for the current-voltage (ID-VC) curves of the contact region, and a parameter extraction procedure, in which a sequence of iterative steps is carried out until a good agreement between experimental and simulated current voltage curves is obtained [2]. The parameter extraction procedure was accelerated in [3] with the proposal of an evolutionary procedure to extract the parameters that best fit experimental current-voltage characteristics. Later in [4], improvements over this evolutionary procedure were presented. Due to the explosion of different applications of OTFTs such as phototransistors and a wide variety of physical and chemical sensors, novel materials, contacts, and designs for transistor were proposed and used. For these applications, more accurate models and better extraction parameter procedures are needed. These new structures impose more requirements to the extraction methods and models, and therefore to the extracted parameters. From this point of view, the evolutionary extraction procedures proposed in [3, 4] are a good option to be used in combination with the above mentioned generic analytical model for the current-voltage (ID-VD) characteristics of OTFTs [1, 2]. In order to adapt both the compact model and the extraction procedure to new applications of the OTFTs, rules are added in form of optimization objectives and constrains for the different parameters. In this work, we present such rules applied to different sets of thin film phototransistors and sensors. In the first place, we consider the multi-objective evolutionary algorithm (MOEA), NSGA-II [5]. It was used in [3, 4], and seeks values of the parameter in the compact model that best meet some user defined objectives. In [3], two objectives were optimized, while in [4], four objectives were optimized, along with some defined constraints. It is known that classic MOEAs, such as the NSGA-II, have serious limitations when coping with more than three objectives. These problems are referred as many-objective optimization problems (MaOPs). Among the limitations of MOEAs to treat MaOPs are the selection operators, computational cost, visualization of the Pareto optimal front (POF), and more importantly, the convergence to an optimal solution. Recently, a many-objective implementation of the NSGA-II, the NSGA-III, was released [5]. NSGA-III was designed to specially deal with MaOPs, incorporating different operators to the ones used by its predecessor. Thus, in a second part of this work, we substitute the NSGA-II algorithm with the NSGA-III one for the characterization of the same sets of OTFTs. Finally, the results of using both algorithms are compared and will be discussed. Acknowledgments This work was supported by projects MAT2016-76892-C3-3-R and TIN2015-67020-P funded by the Spanish Government, European Regional Development Funds (ERDF) and the Canada Research Chair Program.

Electrical Properties of GaAs Nanowires Grown on Graphene/SiC Hybrid Substrates

The electrical properties of GaAs nanowires grown on a 6H-SiC (0001) substrate covered with graphene single layers and bilayers are studied. The nanowires are grown by molecular-beam epitaxy, with gold as a catalyst. The electrical properties are studied by measuring and analyzing the current–voltage characteristics of single nanowires vertically grown on a substrate. Numerical simulation of the experimental current–voltage curves revealed the presence of a ~0.6-V-high Schottky barrier between the nanowires and graphene. The appearance of the barrier is due to the formation of excess arsenic at the nanowire/graphene interface.

Electrical Study of Pentacene-Based Metal–Semiconductor–Metal Structure: Schottky Barrier and Active Layer Thickness Effects

The impact of electrodes and active layer thickness on the current–voltage characteristics of Au/Pentacene/Al structure was studied using a physicallybased 2-D simulation by solving Poisson’s, continuity, and drift diffusion equations. The main parameters required for simulation are extracted from the logarithmic representation of experimental current–voltage curves. The simulation results produce an excellent overlapping with the experimental data after including parameters previously found in our model. Finally, the simulation was used to better understand the physical processes together with mechanisms governing the efficiency of the device under investigation and to have a predictive behavior.

Kinetic mechanism of current-time curves of peptide ion channels in lipid membranes

The three-state kinetic model developed in our previous paper (R. Guidelli and L. Becucci, 2016), which explains all the main features of experimental current-voltage curves of peptide ion channels at conventional bilayer lipid membranes (BLMs), is extended to explain some still unsettled features of the corresponding voltage-step current-time (I-t) curves. To this end, the time dependence of the open probability of peptide ion channels during the first few seconds from the instant of the voltage step, before the attainment of its steady-state value expressed by the well-known one-sided Boltzmann equation, is taken into account. This approach explains the reason for the different behavior of the experimental sigmoidal I-t curves with respect to the wholly concave downward ones; the frequent occurrence of concave downward I-t curves characterized by a time course describable by a sum of two exponential functions is also justified. On the other hand, the three-state kinetic model disproves the validity of the experimental procedure aiming at estimating the gating charge of peptide ion channels from the initial stage of the time derivative of ON and OFF ionic currents, commonly justified by an unproved analogy with gating currents of potassium ion channels.

Design and characterization of hybrid III–V concentrator photovoltaic–thermoelectric receivers under primary and secondary optical elements

Lattice-matched monolithic triple-junction Concentrator Photovoltaic cells (InGa(0.495)P/GaIn(0.012)As/Ge) were electrically and thermally interfaced to two Thermoelectric Peltier module designs. An electrical and thermal model of the hybrid receivers was modelled in COMSOL Multiphysics software v5.3 to optimize cell cooling whilst increasing photon energy conversion efficiency. The receivers were measured for current–voltage characteristics with the cell only (with sylguard encapsulant), under single secondary optical element at x2.5 optical concentration, and under Fresnel lens primary optical element concentration between x313 and x480. Measurements were taken in solar simulators at Cardiff and Jaén Universities, and on-sun with dual-axis tracking at Jaén University. The hybrid receivers were electrically, thermally and theoretically investigated. The electrical performance data for the cells under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The performance of six hybrid devices were evaluated within two 3-receiver strings under primary optical concentration with measured acceptance angles of 1.00° and 0.89°, similar to commercially sourced Concentrator Photovoltaic modules. A six-parameter one-diode equivalent electrical model was developed for the multi-junction cells under both primary and secondary optical concentration. This was applied to extract six model parameters with the experimental current–voltage curves of type A receiver at 1, 3 and 500 concentration ratios. Standard test conditions (1000 W/m2, 25 °C and Air Mass 1.5 Global spectrum) were assumed based on trust-region-reflective least squares algorithm in MATLAB. The model fitted the experimental current–voltage curves satisfactorily with a mean error of 4.44%. The combined primary and secondary optical intensity gain coefficient is as high as 0.92, in comparison with 0.50–0.86 for crossed compound parabolic concentrators. The determined values of diode reverse saturation current, combined series resistance and shunt resistance were similar to those of monocrystalline PV cell/modules in our previous publications. The model may be applicable to performance prediction of multi-junction CPV cells in the future.

Plausible carrier transport model in organic-inorganic hybrid perovskite resistive memory devices

We demonstrate thermally assisted hopping (TAH) as an appropriate carrier transport model for CH3NH3PbI3 resistive memories. Organic semiconductors, including organic-inorganic hybrid perovskites, have been previously speculated to follow the space-charge-limited conduction (SCLC) model. However, the SCLC model cannot reproduce the temperature dependence of experimental current-voltage curves. Instead, the TAH model with temperature-dependent trap densities and a constant trap level are demonstrated to well reproduce the experimental results.

Электрические свойства GaAs нитевидных нанокристаллов, выращенных на гибридных подложках графен/SiC

AbstractThe electrical properties of GaAs nanowires grown on a 6 H -SiC (0001) substrate covered with graphene single layers and bilayers are studied. The nanowires are grown by molecular-beam epitaxy, with gold as a catalyst. The electrical properties are studied by measuring and analyzing the current–voltage characteristics of single nanowires vertically grown on a substrate. Numerical simulation of the experimental current–voltage curves revealed the presence of a ~0.6-V-high Schottky barrier between the nanowires and graphene. The appearance of the barrier is due to the formation of excess arsenic at the nanowire/graphene interface.

A scaling law for monocrystalline PV/T modules with CCPC and comparison with triple junction PV cells

Scaling laws serve as a tool to convert the five parameters in a lumped one-diode electrical model of a photovoltaic (PV) cell/module/panel under indoor standard test conditions (STC) into the parameters under any outdoor conditions. By using the transformed parameters, a current-voltage curve can be established under any outdoor conditions to predict the PV cell/module/panel performance. A scaling law is developed for PV modules with and without crossed compound parabolic concentrator (CCPC) based on the experimental current-voltage curves of six flat monocrystalline PV modules collected from literature at variable irradiances and cell temperatures by using nonlinear least squares method. Experiments are performed to validate the model and method on a monocrystalline PV cell at various irradiances and cell temperatures. The proposed scaling law is compared with the existing one, and the former exhibits a much better accuracy when the cell temperature is higher than 40°C. The scaling law of a triple junction flat PV cell is also compared with that of the monocrystalline cell and the CCPC effects on the scaling law are investigated with the monocrystalline PV cell. It is identified that the CCPCs impose a more significant influence on the scaling law for the monocrystalline PV cell in comparison with the triple junction PV cell. The proposed scaling law is applied to predict the electrical performance of PV/thermal modules with CCPC.

Memristive device based on a depletion-type SONOS field effect transistor

State-of-the-art SONOS (silicon-oxide-nitride-oxide-polysilicon) field effect transistors were operated in a memristive switching mode. The circuit design is a variation of the MemFlash concept and the particular properties of depletion type SONOS-transistors were taken into account. The transistor was externally wired with a resistively shunted pn-diode. Experimental current–voltage curves show analog bipolar switching characteristics within a bias voltage range of ±10 V, exhibiting a pronounced asymmetric hysteresis loop. The experimental data are confirmed by SPICE simulations. The underlying memristive mechanism is purely electronic, which eliminates an initial forming step of the as-fabricated cells. This fact, together with reasonable design flexibility, in particular to adjust the maximum RON/ROFF ratio, makes these cells attractive for neuromorphic applications. The relative large set and reset voltage around ±10 V might be decreased by using thinner gate–oxides. The all-electric operation principle, in combination with an established silicon manufacturing process of SONOS devices at the Semiconductor Foundry X-FAB, promise reliable operation, low parameter spread and high integration density.

Rectifcation of Ion Current Determined by the Nanopore Geometry: Experiments and Modelling**Supported by the National Natural Science Foundation of China under Grant Nos 61471336, 51503207 and 61504146, and the Joint-Scholar of West Light Foundation of Chinese Academy of Sciences.

We provide a way to precisely control the geometry of a SiNx nanopore by adjusting the applied electric pulse. The pore is generated by applying the current pulse across a SiNx membrane, which is immersed in potassium chloride solution. We can generate single conical and cylindrical pores with different electric pulses. A theoretical model based on the Poisson and Nernst—Planck equations is employed to simulate the ion transport properties in the channel. In turn, we can analyze pore geometries by fitting the experimental current-voltage (I–V) curves. For the conical pores with a pore size of 0.5–2nm in diameter, the slope angles are around −2.5° to −10°. Moreover, the pore orifice can be enlarged slightly by additional repeating pulses. The conic pore lumen becomes close to a cylindrical channel, resulting in a symmetry I–V transport under positive and negative biases. A qualitative understanding of these effects will help us to prepare useful solid-nanopores as demanded.

Short channel effects in graphene-based field effect transistors targeting radio-frequency applications

Channel length scaling in graphene field effect transistors (GFETs) is key in the pursuit of higher performance in radio frequency electronics for both rigid and flexible substrates. Although two-dimensional (2D) materials provide a superior immunity to short channel effects (SCEs) than bulk materials, they could dominate in scaled GFETs. In this work, we have developed a model that calculates electron and hole transport along the graphene channel in a drift-diffusion basis, while considering the 2D electrostatics. Our model obtains the self-consistent solution of the 2D Poisson’s equation coupled to the current continuity equation, the latter embedding an appropriate model for drift velocity saturation. We have studied the role played by the electrostatics and the velocity saturation in GFETs with short channel lengths Severe scaling results in a high degradation of GFET output conductance. The extrinsic cutoff frequency follows a scaling trend, where the index fulfills The case corresponds to long-channel GFETs with low source/drain series resistance, that is, devices where the channel resistance is controlling the drain current. For high series resistance, decreases down to and it degrades to values of because of the SCEs, especially at high drain bias. The model predicts high maximum oscillation frequencies above 1 THz for channel lengths below 100 nm, but, in order to obtain these frequencies, it is very important to minimize the gate series resistance. The model shows very good agreement with experimental current voltage curves obtained from short channel GFETs and also reproduces negative differential resistance, which is due to a reduction of diffusion current.