Calculated Current Voltage Research Articles

Hydrogenated cove-edge aluminum nitride nanoribbons for ultrascaled resonant tunneling diode applications: a computational DFT study

While synthesizing quasi-one-dimensional nanoribbons, there is a finite probability that edges have cove-edge defects. This paper focuses on the structural, electronic, and transport properties of cove-edge aluminum nitride nanoribbons (AlNNR) using density functional theory and the non-equilibrium Green’s function (NEGF) method. The cove-edge AlNNRs are thermodynamically stable and exhibit metallic behavior. Interestingly, the calculated current–voltage characteristics of the cove-edge AlNNR-based nanodevices show negative differential resistance (NDR). The H-AlN-Cove nanodevice exhibits high peak-to-valley current ratio (PVCR) of the order of 107. The calculated PVCR of the H-AlN-Cove nanodevice is 106 times higher than that of the silicene nanoribbon (SiNR) and graphene nanoribbon (GNR), and 104 times higher than that of the phosphorene nanoribbon (PNR) and arsenene nanoribbons (ANR)-based devices respectively. The NDR feature with high PVCR provides a prospect for the cove-edge AlNNR in nanodevice applications.

Gap distance dependence on field emission at the nanogap between silicon cleavage surfaces

In this study, we developed a model of field emission at a vacuum nanogap composed of semiconductor electrodes and conducted numerical calculations to evaluate its field emission characteristics. The current at the silicon nanogap was also measured, and the results were compared with the calculated results. Large-area vacuum nanogaps are expected to be used for highly efficient room-temperature thermionic power generation owing to their good thermal insulation, and their electrical conduction of tunneling current is sufficient for practical use. Because vacuum nanogaps should be parallel and smooth with a large area, we proposed and examined the use of cleavage to fabricate nanogaps in single-crystal materials. A nanogap with a nominal area of 26.5 μm2 was fabricated in a microelectromechanical device to evaluate its properties, and the model was used for the analysis. The calculated current–voltage characteristics of the semiconductor nanogap of both n-type and p-type silicon were affected by the bandgap and the presence of carriers, i.e., electrons and holes. Moreover, the Fowler–Nordheim plot was confirmed to be valid for semiconductor nanogaps based on the calculated results. We proposed an effective work function that compensates for the discrepancy between semiconductor nanogaps and the Fowler–Nordheim theory and enables a more accurate analysis. Field-emission currents flowing through a 1.1 nm nanogap were measured and matched with the calculated results by adjusting the field enhancement factor and emission area. The model developed and confirmed experimentally in this work will be helpful in examining field emissions at semiconductor nanogaps.

Performance characteristic of a PV module as influenced by dust accumulation: theory versus experiment

This paper is aimed at assessing by theory and experiment the current–voltage and power-voltage characteristics of a PV module as influenced by dust accumulation. A method is proposed in a computer code to follow-up an incident solar radiation through the module layers considering the reflection and transmission of radiation at the interfaces between the layers to evaluate how the incident radiation is attenuated before reaching the module. Also, absorption of radiation in the dust layer and the glass cover is considered. The evaluation of the reflectance and transmittance calls for analysis of the accumulated dust to identify its constituents using X-ray fluorescence apparatus. The refractive and absorption indices are assessed for dust constituents as well as the corresponding effective values for the sample as a whole. The current–voltage characteristic of the dusty module is calculated using Simulink with consideration of module parameters after being corrected according to the incident radiation received by the solar cell and the ambient temperature where the module is installed. The calculated current–voltage and power-voltage characteristics of the dusty module agreed reasonably with the measured ones for a 175-W module as the incident radiation decreased to 68% due to dust accumulation with a subsequent decrease of the maximum output power of dusty module by 31% when compared with the clean one. The percentage decrease of short-circuit current recorded 31% due to dust deposition against 2% for the increase of open-circuit voltage at ambient temperature of 44 °C and incident solar radiation of 1027 W/m2. This conforms to previous findings in the literature.

Stochastic behavior of an interface-based memristive device

A large number of simulation models have been proposed over the years to mimic the electrical behavior of memristive devices. The models are based either on sophisticated mathematical formulations that do not account for physical and chemical processes responsible for the actual switching dynamics or on multi-physical spatially resolved approaches that include the inherent stochastic behavior of real-world memristive devices but are computationally very expensive. In contrast to the available models, we present a computationally inexpensive and robust spatially 1D model for simulating interface-type memristive devices. The model efficiently incorporates the stochastic behavior observed in experiments and can be easily transferred to circuit simulation frameworks. The ion transport, responsible for the resistive switching behavior, is modeled using the kinetic cloud-in-a-cell scheme. The calculated current–voltage characteristics obtained using the proposed model show excellent agreement with the experimental findings.

Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model* *Project supported by the National Key Basic Research and Development Program of China (Grant No. 2017YFA0304003), the National Natural Science Foundation of China (Grant Nos. U1831202, U1731119, U1931123, 11773083, and 11873099), the Chinese Academy of Sciences (Grant Nos. QYZDJ-SSWSLH043 and GJJSTD20180003), and Jiangsu Province, China

Optical superconducting transition-edge sensor (TES) has been widely used in quantum information, biological imaging, and fluorescence microscopy owing to its high quantum efficiency, low dark count, and photon number resolving capability. The temperature sensitivity (αI ) and current sensitivity (βI ) are important parameters for optical TESs, which are generally extracted from the complex impedance. Here we present a method to extract αI and βI based on a two-fluid model and compare the calculated current–voltage curves, pulse response, and theoretical energy resolution with the measured ones. This method shows qualitative agreement that is suitable for further optimization of optical TESs.

A Single‐Molecule and Logic Gate via Optical and Acid–Base Control

AbstractSingle‐molecule electronics is a promising solution for electronic device miniaturization. While controllable molecular logic gates are particularly attractive because they are the primary element and can accomplish logical operation reliable and repeatedly for practical application. Here, a brand‐new molecule, which is constructed from a light‐switchable azobenzene unit and proton‐switchable pyrimidine unit, is reported. The electronic transport properties of the molecule are theoretically investigated by density functional theory (DFT) combined with non‐equilibrium Green's function method (NEGF). The calculated current–voltage curves show that the molecule system produces a low resistance only when the ultraviolet (UV) light and acid solution are applied, otherwise, a high resistance will be obtained. Therefore, the molecule system can behave as a single‐molecule AND logic gate which can be controlled by two orthogonal inputs: protonation and light. This work demonstrates a feasible perspective for creating single‐molecule logic gate device.

Microscopic Tunneling Model of Nb–AlN–NbN Josephson Flux-Flow Oscillator

Since the very first experimental realization of a Josephson flux-flow oscillator (FFO), its theoretical description has been limited by the phenomenological perturbed sine-Gordon equation (PSGE). While PSGE can qualitatively describe the topological excitations in Josephson junctions that are sine-Gordon solitons or fluxons, it is unable to capture essential physical phenomena of a realistic system such as the coupling between tunnel currents and electromagnetic radiation. Furthermore, PSGE neglects any dependence on energy gaps of superconductors and makes no distinction between symmetric and asymmetric junctions: those made of two identical or two different superconducting materials. It was not until recently when it became possible to calculate properties of FFO by taking into account information about energy gaps of superconductors (Gulevich et al. in Phys Rev B 96:024215, 2017). Such approach is based on the microscopic tunneling theory and has been shown to describe essential features of symmetric Nb–AlO\(_\mathrm{x}\)–Nb junctions. Here, we extend this approach to asymmetric Nb–AlN–NbN junctions and compare the calculated current–voltage characteristics to our experimental results.

Model for large magnetoresistance effect in p–n junctions

We present a simple model based on the classic Shockley model to explain the magnetotransport in nonmagnetic p–n junctions. Under a magnetic field, the evaluation of the carrier to compensate Lorentz force establishes the necessary space-charge region distribution. The calculated current–voltage (I–V) characteristics under various magnetic fields demonstrate that the conventional nonmagnetic p–n junction can exhibit an extremely large magnetoresistance effect, which is even larger than that in magnetic materials. Because the large magnetoresistance effect that we discussed is based on the conventional p–n junction device, our model provides new insight into the development of semiconductor magnetoelectronics.

Arsenic Phosphorus Monolayer: A Promising Candidate for H2S Sensor and NO Degradation With High Sensitivity and Selectivity

The sensing behaviors of arsenic phosphorus (AsP) for nitric oxide (NO) and hydrogen sulfide (H2S) are investigated by means of the density functional theory and the nonequilibrium Green’s function method. The calculated adsorption energy and charge transfer of H2S molecule on silicon-doped AsP (Si-AsP) are 0.352 eV and 0.106 ${e}$ , respectively, indicating the presence of physisorption process. The H2S adsorption on aluminum-doped AsP is a chemisorption process with covalent bond formed. Furthermore, the calculated current–voltage ( ${I}$ – ${V}$ ) relation clearly shows that the substrate with and without H2S adsorption exhibits distinct responses. This property indicates that Si-AsP is expected to be the high-performance H2S sensor. The chemisorption is also observed in Si-/Al-doped AsP with NO molecule adsorption, suggesting the high potential in the application of NO degradation.

Simulation of electron transport in GaAs/AlAs superlattices with a small number of periods for the THz frequency range

The electron transport in superlattices based on GaAs/AlAs heterostructures with a small number of periods (6 periods) is calculated by the Monte Carlo method. These superlattices are used in terahertz diodes for the frequency stabilization of quantum cascade lasers in the range up to 4.7 THz. The band structure of superlattices with different numbers of AlAs monolayers is considered and their current–voltage characteristics are calculated. The calculated current–voltage characteristics are compared with the experimental data. The possibility of the efficient application of these superlattices in the THz frequency range is established both theoretically and experimentally.

A procedure to calculate the I – V characteristics of thin-film photovoltaic modules using an explicit rational form

Abstract Accurate models of the electrical behaviour of photovoltaic modules are effective tools for system design. One or two diode equivalent circuits have been widely used even though some mathematical difficulties were found dealing with implicit equations. In this paper, a new model based on a simple rational function, which does not contain any implicit exponential form, is presented. The model was conceived in order to be used with thin-film photovoltaic modules, whose current–voltage curves are characterised by very smooth shapes. The parameters of the model are evaluated by means of the derivatives of the issued characteristics in the short circuit and open circuit points at standard rating conditions, and assuming that the calculated current–voltage curve contains the rated maximum power point of the simulated panel. The capability of the model to calculate the current–voltage characteristic for values of the solar irradiance and cell temperature far from the standard rating conditions was verified for various thin-film technologies, such as CIS, CIGS, amorphous silicon, tandem and triple-junctions photovoltaic modules. A comparison with the results obtained by another rational model and other two-diode models, which were used to simulate the electrical behaviour of thin-film photovoltaic modules, is also presented.

Computational study of temporal behavior of incident species impinging on a water surface in dielectric barrier discharge for the understanding of plasma–liquid interface

A lipid bilayer is a basic structure of the cell membrane and is stable in liquid solution. In this study, we analyzed dielectric barrier discharge (DBD) containing water on a quartz substrate using a one-dimensional fluid model. To simulate atmospheric pressure plasma for practical use, a tiny amount of N2 gas (0.5 ppm) was added to He gas ambient as an impure gas. The calculated current–voltage (I–V) characteristics reproduced the measured ones qualitatively. We focused on the behavior of DBD at the plasma–liquid interface and analyzed the temporal behavior of the electric field strength and incident fluxes of charged, excited, and radical species on the water surface. By varying the gap length, it was shown that the maximum electric field strength in an AC cycle saturated at gap lengths ≥0.15 cm. The incident fluxes of N2+ and He2+ on the water surface are almost the same and show strong correlations with the electric field in the vicinity of the water surface.

Tip-contact related low-bias negative differential resistance and rectifying effects in benzene-porphyrin-benzene molecular junctions.

The electronic transport properties of benzene-porphyrin-benzene (BPB) molecules coupled to gold (Au) electrodes were investigated. By successively removing the front-end Au atoms, several BPB junctions with different molecule-electrode contact symmetries were constructed. The calculated current-voltage (I-V) curves depended strongly on the contact configurations between the BPB molecules and the Au electrodes. In particular, a significant low-voltage negative differential resistance effect appeared at -0.3 V in the junctions with pyramidal electrodes on both sides. Along with the breaking of this tip-contact symmetry, the low-bias negative differential resistance effect gradually disappeared. This tip-contact may be ideal for use in the design of future molecular devices because of its similarity with experimental processes.

DC negative corona discharge in atmospheric pressure helium: transition from the corona to the ‘normal’ glow regime

Direct current (dc) negative corona discharges in atmospheric pressure helium are simulated via detailed numerical modeling. Simulations are conducted to characterize the discharges in atmospheric helium for a pin plate electrode configuration. A self-consistent two-dimensional hybrid model is developed to simulate the discharges and the model predictions are validated with experimental measurements. The discharge model considered consists of momentum and energy conservation equations for a multi-component (electrons, ions, excited species and neutrals) gas mixture, conservation equations for each component of the mixture and state relations. A drift–diffusion approximation for the electron and the ion fluxes is used. A model for the external circuit driving the discharge is also considered and solved along with the discharge model. Many of the key features of a negative corona discharge, namely non-linear current–voltage characteristics, spatially flat cathode current density and glow-like discharge in the high current regime are displayed in the predictions. A transition to the ‘normal’ glow discharge from the corona discharge regime is also observed. The transition is identified from the calculated current–voltage characteristic curve and is characterized by the radial growth of the negative glow and the engulfment of the cathode wire.

Basic mathematical model of overlimiting transfer enhanced by electroconvection in flow-through electrodialysis membrane cells

Mechanisms for overlimiting current and concentration polarization in electrodialysis (ED) with ion-exchange membranes are not yet well understood despite its half-century history. A first-principles model involving the Nernst–Planck–Poisson equations fully coupled to the Navier–Stokes equations and containing no adjustable parameters is proposed. The calculated current–voltage (I–V) curve of an ED flow-through cell shows a linear region, a sloped plateau surpassing “limiting” current and a rapidly rising region characterized by increasing current oscillations. This curve and concentration profiles are compared with experimental data and with “classical” models. It is shown that the initial smooth region of the I–V plateau relates to a new electrokinetic mode, which is similar to the Dukhin–Mishchuk regime. The difference is in the fact that in the case of forced convection the tangential electric force producing stable electroconvection can appear at a homogeneous flat membrane due to nonuniformity in the lateral concentration distribution; membrane surface nonflatness or electric heterogeneity are not necessary. The oscillating region with a higher slope relates to the Rubinstein–Zaltzman unstable electrokinetic mode. I–V curves calculated with the no-slip and the Navier slip conditions are compared.

Simulation and modelling of charge transport in dye-sensitized solar cells based on carbon nano-tube electrodes

For a better understanding of the mechanisms of dye-sensitized solar cells (DSSCs), based on carbon nano-tube (CNT) electrodes, a phenomenological model is proposed. For modelling purposes, the meso-scopic porous CNT electrode is considered as a homogeneous nano-crystalline structure with thickness L. The CNT electrode is covered with light-absorbing dye molecules, and interpenetrated by the tri-iodide (I−/I3−) redox couple. A simulation platform, designed to study coupled charge transport in such cells, is presented here. The work aims at formulating a mathematical model that describes charge transfer and charge transport within the porous CNT window electrode. The model is based on a pseudo-homogeneous active layer using drift–diffusion transport equations for free electron and ion transport. Based on solving the continuity equation for electrons, the model uses the numerical finite difference method. The numerical solution of the continuity equation produces current–voltage curves that fit the diode equation with an ideality factor of unity. The calculated current–voltage (J–V) characteristics of the illuminated idealized DSSCs (100 mW cm−2, AM1.5), and the different series resistances of the transparent conductor oxide (TCO) layer were introduced into the idealized simulated photo J–V characteristics. The results obtained are presented and discussed in this paper. Thus, for a series resistance of 4 Ω of the TCO layer, the conversion efficiency (η) was 7.49% for the CNT-based cell, compared with 6.11% for the TiO2-based cell. Two recombination kinetic models are used, the electron transport kinetics within the nano-structured CNT film, or the electron transfer rate across the CNT–electrolyte interface. The simulations indicate that both electron and ion transport properties should be considered when modelling CNT-based DSSCs and other similar systems. Unlike conventional polycrystalline solar cells which exhibit carrier recombination, which limits their efficiency, the CNT matrix (in CNT-based cells) serves as the conductor for majority carriers and prevents recombination. This is because of special conductivity and visible–near-infrared transparency of the CNT. Charge transfer mechanisms within the porous CNT matrix and at the semiconductor–dye–electrolyte interfaces are described in this paper.

Do Stone–Wales Defects Alter the Magnetic and Transport Properties of Single-Walled Carbon Nanotubes?

Finite zigzag single-walled carbon nanotubes (SWCNTs) of some nanometers in length and modified by a topological defect of the Stone–Wales type were investigated by density functional theory (DFT) computation. Geometric changes of the regular hexagonal reference structures as well as alterations of their energetic, magnetic, and transport characteristics induced by the presence of the defect are recorded and discussed as a function of the tube length. SWCNT prototypes with hydrogen and fullerene hemisphere termination and center as well as edge site defects are included in this study. The resulting four basic system types are characterized in terms of the Stone–Wales defect stabilization energy as well as the energy gaps of the systems with and without Stone–Wales defects. Whereas the magnetism of a zigzag SWCNT reacts sensitively to the nature and number of external adsorbates, it remains unaffected by the presence of Stone–Wales defects. However, the calculated current–voltage characteristic for a repre...

Current simulation of symmetric contacts on CdTe

This article presents the calculated current–voltage characteristics of symmetric Metal–Semiconductor–Metal configurations for Schottky, Ohmic, and injecting-Ohmic contacts on high resistivity CdTe. The results clearly demonstrate that in the wide band-gap, semi-insulating semiconductors, such as high resistivity CdTe, the linearity of the I–V curves cannot be considered a proof of the ohmicity of the contacts. It is shown that the linear I–V curves are expected for a wide range of contact barriers. Furthermore, the slope of these linear curves is governed by the barrier height, rather than the bulk doping concentration. Therefore the deduction of bulk's resistivity from the I–V curves may be false.

Transport properties of carbon atomic wire in the environment of H 2O molecules: An ab initio study

The transport properties of carbon atomic wire in the environment of H 2O molecules are studied by the non-equilibrium Green function method based on density functional theory. In particular, the carbon wire with seven atoms sandwiched between the Al(1 0 0) electrodes is considered. It is found that the transport properties are sensitive to the variation of the number and the position of the H 2O molecule adsorbed on the carbon wire. To our surprise, with different positions of a single H 2O molecule on the carbon wire, the equilibrium conductance shows an evident odd–even oscillatory behavior. For example, the equilibrium conductance of the carbon wire becomes bigger when the H 2O is adsorbed on the odd-numbered carbon atoms; an opposite conclusion is obtained for the H 2O adsorbed on the even-numbered carbon atoms. For the cases of two H 2O molecules, the equilibrium conductance varies largely and the contribution of the third eigenchannel becomes larger in some special configurations. The calculated current–voltage curves show different behavior with the variation of the positions of the H 2O molecules. In certain cases, large negative differential resistance (NDR) is shown, while in other cases, it only slightly deviates from the linear behavior. The above behavior is analyzed via the charge transfer and the density of states (DOS) and reasonable explanations are presented.

Numerical method for the extraction of photovoltaic module double-diode model parameters through cluster analysis

A numerical procedure for the extraction of the double-diode model parameters of photovoltaic (PV) modules is described. A particle swarm optimization algorithm is used to fit the calculated current–voltage characteristic of a PV module to the experimental one. As no recurrent solution was found in the large number of simulations carried out, mainly because of the stochastic nature of the optimization algorithm, statistics in combination with cluster analysis was employed to give an insight into the PV module parameters. This approach allows one to obtain a set of parameters which is reasonable and representative of the physical system.