Measurements Of Current-voltage Characteristics Research Articles

Atmospheric pressure high-power impulse plasma source for deposition of metallic coatings

Abstract

Extracting voltage-dependent series resistance of single diode model for organic solar cells

In this paper, a modified equivalent circuit model is proposed to elucidate the electrical behavior of Organic Solar Cells (OSCs). In this way, this single diode model uses a voltage-dependent series resistance to enhance the modeling accuracy while benefiting from the simplicity of the equivalent circuit. The voltage dependency of the series resistance of OSCs is mainly related to internal processes of charge extraction and charge transport. The charge extraction at electrodes is influenced by space charge effect and many other physical parameters including exciton lifetime, dissociation rate, and free carrier recombination.The carrier transport process from donor/acceptor interface to electrodes is governed by its mobility. On the other hand, carrier mobility of organic material depend on field variation. The voltage-dependent series resistance is not often used in the today’s OSC circuit models due to a lack of a reliable field-dependent extraction approach. This proposed model expands its application in finding optimum bias, behavior analysis and efficiency improvement of OSCs. At first, a genetic algorithm curve fitting is applied to the measured current–voltage characteristics to extract the model’s parameters assuming an average constant series resistance. Then a new algorithm is proposed for extracting the voltage-dependent series resistance. Finally, consistency of the extracted field dependent series resistance with previous literature is presented. The results shows that the average mean square errors of the predicted J–V characteristics by the proposed approach for five cells under test is improved by a factor of $$10^{6}$$ in comparison with those of a constant value $$R_{s}$$ approach. This is the first successful extraction of voltage dependent series resistance of OSCs from DC current–voltage characteristic.

Characterization of an InAs/GaSb type-II superlattice barrier photodetector operating in the LWIR domain

In this paper, structural, optical and electrical characterizations of longwave infrared barrier detectors based on the InAs/GaSb superlattice are reported and analyzed. The fabricated detectors exhibited a 50% cut-off wavelength around 10.5 μm at 80K measured by photoluminescence and spectral response. The dark current density was 8.4×10-4 A/cm2 at 80K and a performance analysis combining spectral response, dark current-voltage characteristic and capacitance-voltage measurement curves was performed to determine the operating bias and the dark current regimes at different biases. Dark current simulations were also performed to better understand limiting dark current mechanisms of the device performance.

Extraction of Intrinsic Properties of the Accumulation Channel in an Organic Field‐Effect Transistor

An organic field‐effect transistor based on a squaraine fiber is studied, where the electric conductance values of the bulk and accumulation channel are comparable. The measured current–voltage characteristics are decomposed into two components, one representing the bulk and the other the accumulation channel. For small gate voltage (Vg), the output characteristics of the channel are described as a superposition of the Ohmic, space‐charge‐limited current, and trap‐filled‐limited (TFL) conduction mechanisms. The traps near the source are filled with electrons injected from source via the source‐gate electric field, but the traps near the drain could be filled only with the source‐drain electric field (Vd). The higher the gate voltage, the larger is the density of electrons injected from the source into the accumulation channel, the larger the density of free electrons, the larger the density of the trapped electrons, and the larger the drain voltage up to which the modified Child's law exists. θ is the fraction of the free electrons. For large voltage Vg, all traps are filled with the source‐gate electric field, and, as a result, only Ohm's and Child's laws () are observed. The electron mobility in the accumulation channel features a linear dependence on the gate voltage.

Structural, chemical, and electrical parameters of Au/MoS2/n-GaAs metal/2D/3D hybrid heterojunction

In this study, Au/MoS2/n-GaAs heterojunction is fabricated with single MoS2 layer and its structural, chemical and electrical parameters are investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and measurement of current-voltage (I-V) characteristics at room temperature. XRD and XPS analysis results confirm the formation of MoS2 layer on the n-GaAs surface. The electrical properties of the Au/MoS2/n-GaAs heterojunction are compared with those of the Au/n-GaAs Schottky junction. Interestingly, the heterojunction possesses a higher barrier height, lower leakage current and higher rectification ratio, in comparison with the Schottky junction. The shunt resistance (RSh) and series resistance (RS) are also assessed for both the junctions. Moreover, the ideality factor (n), barrier height (Φb) and series resistance (RS) are evaluated using Norde, Cheung’s and surface potential (ΨS-V) plots and the results are well-matched. Furthermore, the current transport mechanism is analyzed based on the forward bias I-V data. Lastly, the Poole-Frenkel emission conduction mechanism is employed to control the reverse bias I-V behavior of both Au/n-GaAs Schottky junction and Au/MoS2/n-GaAs heterojunction. The results demonstrate that the Au/MoS2/n-GaAs heterojunction fabricated using a simple technique is suitable for high-quality electronic and optoelectronic device applications.

Influence of Low-Temperature Annealing on the Electrical Conductivity of SiOx Films

In this paper, the results on the conductivity of silicon enriched SiOx films and the influence of low temperature annealing at 450 °C in the H2 and vacuum are presented. SiOx films were prepared on Si substrate by low pressure chemical vapor deposition (LP CVD) with using SiH4, N2O as the precursor gases and H2 as a carrier gas. The measurements of current-voltage characteristics were carried out in the wide temperature range 95-334 K. It was revealed that the influence of atmosphere of the low temperature annealing is significant. In general case it was established that after the annealing of the initial film in the hydrogen the conductivity increases and after annealing in the vacuum decreases. Characteristic feature of all films (without and with annealing) is the conductivity according to the Mott’s law at low voltages (U < 1 V) in temperature range 295 < T < 345 K. The calculated densities of electron states (traps) in bandgap near the Fermi level from slope of curves in Mott’s coordinate are equal to N = 2.12 × 1017 eV−1 × cm−3 (initial film), N = 4.14 × 1019 eV−1 × cm−3, (H2), N = 6.62 × 1016 eV−1 × cm−3 (vacuum). At higher voltages and lower temperature another transport mechanisms have been revealed. Among them are space-charge limited current (SCLC), Poole-Frenkel mechanism and Fowler-Nordheim tunneling.

Study of the effect of an external magnetic field on the photoelectric properties of a copper phthalocyanine film

In the article the results of a study of the influence of a magnetic field on the change in current-voltage char- acteristics and charge carrier mobility in a solid film of copper phthalocyanine (CuPc) are presented. A solid CuPc film on a substrate with a conductive ITO surface (Indium Tin Oxide) was obtained by thermal evapo- ration in a vacuum. The absorption spectrum of CuPc was measured; as a result, copper phthalocyanine mol- ecules on the substrate surface were found to be in the metastable α-phase. Measurements of current-voltage characteristics (IVC) were carried out using a potentiostat-galvanostat P20X in the linear sweep mode. To study the effect of a magnetic field on the photoelectric characteristics, a sample was placed between the poles of an electromagnet. A xenon lamp with radiation intensity of 50 mW/cm2 was used as a simulator of sunlight. As a result of experiments, it was found that the external magnetic field affects the value of the short-circuit current, at the same time, the charge carrier mobility in a magnetic field does not change. The studied effect of a change in the current-voltage characteristics in a solid CuPc film upon application of an external magnetic field can be used as a high-speed magnetic field sensor.

Description and Verification of the Fundamental Current Mechanisms in Silicon Carbide Schottky Barrier Diodes

Attempts to model the current through Schottky barrier diodes using the two fundamental mechanisms of thermionic emission and tunnelling are adversely impacted by defects and second order effects. This has led to the publication of countless different models to account for these effects, including some with non-physical parameters. Recently, we have developed silicon carbide Schottky barrier diodes that do not suffer from second order effects, such as excessive leakage, carrier generation and recombination, and non-uniform barrier height. In this paper, we derive the foundational current equations to establish clear links between the fundamental current mechanisms and the governing parameters. Comparing these equations with measured current–voltage characteristics, we show that the fundamental equations for tunnelling and thermionic emission can accurately model 4H silicon carbide Schottky barrier diodes over a large temperature and voltage range. Based on the obtained results, we discuss implications and misconceptions regarding barrier inhomogeneity, barrier height measurement, and reverse-bias temperature dependencies.

Critical Evaluation of Organic Thin-Film Transistor Models

The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel.

Three site molecular orbital controlled single-molecule rectifiers based on perpendicularly linked porphyrin-imide dyads.

The original single-molecule rectifier proposed by Aviram and Ratner is based on a donor-σ-acceptor structure, in which σ functions as the insulator to disconnect the π electronic systems of the two parts. However, there have been no reports on experimentally demonstrated highly efficient single-molecule rectifiers based on this mechanism. In this paper, we demonstrate single-molecule rectifiers with perpendicularly connected metal porphyrin-imide dyads. Our proposed molecule rectifiers use hydroxyl groups at both ends as weak anchoring groups. Measurements of the single-molecule current-voltage characteristics of these molecules clearly show that the rectification ratio reached a high value of 14 on average. Moreover, the ratio could be tuned by changing the central metal in the porphyrin core. All of these features can be explained by the energy-level shift of the molecular orbital using a model with three electronic parts.

Isothermal measurement of current-voltage characteristics of Gunn diodes with reflection of their discontinuities and hysteresis

Requirements to the measuring setup are formulated, which make it possible obtaining isothermal current-voltage (I-V) characteristics of the Gunn diode with reflection of their discontinuities, region of negative differential resistance, and hysteresis. The influence of the inductance of the test pulses, source on the occurrence of self-excitation in the connecting transmission line is investigated. The maximum permissible values of the inductance of the test signal source are indicated. Operation of the measuring circuit without self-excitation was experimentally achieved in most of the region with negative differential resistance. The isothermal I-V characteristics of the Gunn diode were measured with a controlled systematic error due to the comparing the measurement result with the developed model of the I-V characteristic.

Modeling of silicon-germanium heterojunction bipolar transistors

The results of measurements of current-voltage characteristics of SiGe transistors for different temperatures are presented. The extraction results of parameters of test structures of the silicon-germanium SiGe bipolar transistors are presented.

Materials selection and fabrication nanotechnology of the composite memristor-diode crossbar — the basis of neuroprocessor hardware implementation

To examine the operation of the memory and logic matrices of the neuroprocessor, it is necessary to produce a laboratory composite memristor-diode crossbar, which is the basis of these matrices. For this purpose, the authors of this article have chosen materials and fabrication nanotechnology of Zener diode semiconductor layers and a memristor layer that provide optimal characteristics of the diode and memristors. This article shows that magnetron-sputtering method is optimal for fabrication of both diodes and memristors. Thus, all of composite memristor-diode crossbar layers, including conducting paths, can be fabricated in single technological module. ZnOx was chosen as the n-type semiconductor, the carrier concentration in which is controlled by changing the stoichiometry of the compound during reactive magnetron sputtering. The second p-type layer of the diode was obtained by magnetron sputtering of a silicon target doped with boron. The results show that for the p-Si/ZnOx heterojunction, there is an optimal molar fraction of zinc, which provides the best characteristics of the diode, and an increase in the doping level of the p-Si layer leads to an increase in the nonlinearity of the current-voltage characteristic and a decrease in the voltage of the reversible breakdown. The greatest stability of electrical parameters — switching voltages and resistances in high-conductive and low-conductive states — was achieved in a memristor with doped titanium oxide W/TixAl1-xOy/TiN, which is due not only to the choice of mixed oxide, but also to the choice of its fabrication technology. The measured current-voltage characteristics of separate cells prove the operability of fabricated memristor-diode crossbar. The authors show that the high resistance of the closed diode leads to the almost complete disappearance of the reverse branch of the memristor current — voltage characteristic, since the small resistance of the memristor is lost against the background high resistance of the diode. The developed unified nanotechnology for fabricating a combined memristor-diode crossbar allows the production of ultra-large memory and logic matrices of a neuroprocessor based on one technological module with reactive magnetron sputtering.

Research of influence Al on luminescence and dark current-voltage characteristics of InAs/GaAs heterostructures

A study was made of AlxGa1-xAs wide-bandgap potential barriers influence on photoluminescence and dark current-voltage characteristics of InAs/GaAs heterostructures obtained by an ion-beam deposition method. It was established that employing AlxGa1-xAs barriers cause a shift of InAs quantum dots ground-state photoluminescence emission peak in high-energy band (blue shift), increase in intensity and decrease of full width a half at maximum. In addition, the measurements of dark current-voltage characteristics show that increase of Al content in barrier leads to decrease of bias voltage (to 0.48 V) of altering charge carriers transfer mechanism from thermoelectron emission to tunnelling assisted by external electric field. It was established that the use of the Al0.4Ga0.6As potential barrier can produce minimal dark current (10−8 A) in InAs/GaAs heterostructures with quantum dots.

Photoconduction mechanism of ultra-long indium oxide nanowires

Photoelectrical mechanism of single Indium Oxide nanowires have been investigated using current-voltage characteristics measurements varying with temperature. The fabricated In2O3 nanowires show high photosensitivity up to 140 at room temperature. It is shown that the photosensitivity of In2O3 nanowires decreases by increasing the temperature due to shorter carrier life time, higher dark conductance and lower electron mobility at higher temperatures. The significantly enhanced photoconduction of single-In2O3 nanowires observed under UV illumination is attributed mainly to the transition from defect levels, which are introduced by the oxygen vacancies that are mostly present on the surface of the nanowires.

Halide Perovskite Nanopillar Photodetector

Numerous studies have reported the use of halide perovskites as highly functional light-harvesting materials. The development of optimized compositions and deposition approaches has led to impressive improvements; however, no noticeable breakthrough in performance has been observed for these materials recently. Here, a breakthrough that enables the fabrication of vertically grown halide perovskite (VGHP) nanopillar photodetectors via a nanoimprinting crystallization technique is demonstrated. We used engraved nanopatterned polymer stamps to form VGHP nanopillars during the pressurized crystallization of the softly baked gel state of a methylammonium lead iodide (CH3NH3PbI3, denoted MAPI) film. The VGHP films exhibit much lower defect density and higher conductivity, as supported by current-voltage characteristic measurements and conductive atomic force microscopy measurements. Ultimately, two-terminal lateral photodetectors based on the VGHP nanopillar films show a greatly enhanced photoresponse compared with flat film-based photodetectors. We expect that the deposition method presented here will help surpass the technical limits and contribute to further improvements in various halide-perovskite-based devices.

Evaluation of saw damage using diamond-coated wire in crystalline silicon solar cells by photoluminescence imaging

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future.

Auger-generated hot carrier current in photo-excited forward biased single quantum well blue light emitting diodes

We report on measurements of the photo-modulated current-voltage and electroluminescence characteristics of forward biased single quantum well, blue InGaN/GaN light emitting diodes with and without electron blocking layers. Low intensity resonant optical excitation of the quantum well was observed to induce an additional forward current at constant forward diode bias, in contrast to the usual sense of the photocurrent in photodiodes and solar cells, as well as an increased electroluminescence intensity. The presence of an electron blocking layer only slightly decreased the magnitude of the photo-induced current at constant forward bias. Photo-modulation at constant forward diode current resulted in a reduced diode bias under optical excitation. We argue that this decrease in diode bias at constant current and the increase in forward diode current at constant applied bias can only be due to additional hot carriers being ejected from the quantum well as a result of an increased Auger recombination rate within the quantum well.

Tuning of transport properties of the double-step chemical bath deposition grown zinc oxide (ZnO) nanowires by controlled annealing: An approach to generate p-type ZnO nanowires

ZnO nanowires/p-Si heterojunction diodes are fabricated by employing low temperature double-step chemical bath deposition technique. The grown samples are initially annealed at different temperatures in the range of 300 °C to 600 °C at 10 psi argon atmosphere for 30 min. Field emission scanning electron microscope images confirmed the growth of vertically oriented ZnO nanowires with average nanowire diameter and height of 183–190 nm and ~1.4 μm, respectively. The x-ray diffraction study shows that the samples are poly-crystalline with hexagonal wurtzite structure and ZnO nanowires are vertically c-axis oriented. The photoluminescence study indicates the presence of oxygen vacancy in as-grown and 300 °C annealed sample, whereas, the 500 °C annealed ZnO nanowires show the existence of oxygen interstitials. Heterojunction diodes are fabricated on the as-grown, 300 °C, 400 °C, 450 °C, 460 °C, 475 °C, 490 °C, 500 °C, 550 °C and 600 °C annealed nanowires for the measurements of current-voltage and capacitance-voltage characteristics. Both the results indicate an electron dominated transport for the as-grown to 490 °C samples and hole transport for ≥500 °C annealed sample. The acceptor or p-type dopant formation temperature is observed to be 500 °C, which shows an effective acceptor concentration of 1.15 × 1015 cm−3 (at 10 kHz) and 1.74 × 1015 cm−3 (at 1 MHz). Thus the work indicates a possible route for converting the n-type ZnO nanowires to p-type of nature.

Dissipation effects in superconducting heterostructures with tungsten nanorods as weak links

Thin-film hybrid heterostructures formed by superconducting molybdenum-rhenium-alloy films with a critical temperature of about 9 K and nanoscale silicon-based semiconducting interlayers with metallic tungsten nanorods have been fabricated and studied. Current-voltage characteristics of the junctions were measured at 4.2 K and under influence of 11 GHz microwave irradiation. The evidence of a quasi-one-dimensional transport through the tungsten weak links disrupted by phase-slip centers was revealed in MoRe/doped Si/MoRe trilayers under irradiation by a high-frequency field. Also, measured current-voltage characteristics of five-layer MoRe/doped Si/MoRe/doped Si/MoRe devices exhibit a strong influence of a dissipation state in the MoRe interlayer. Namely, the switching from a superconducting state with low dissipation to a finite-conductance regime can be initiated by the emergence of an extra phase-slip center in the MoRe interlayer. Possible physical mechanisms of the two findings are discussed.