Current-voltage Analysis Research Articles

Ballistic transport and optical properties of a new half-metallic monolayer: Vanadium phosphide

In this work, a new monolayer structure, vanadium phosphide (VP) was predicted by first principles approach. Dynamical and thermal stabilities of monolayer VP were confirmed by phonon dispersion and ab initio molecular dynamics calculations. Monolayer VP was found as half-metallic material with an electronic band gap of 1.73 eV in spin down channel, while up spins display metallic band structure yielding a spin-polarized conductivity. However, an applied electric field in perpendicular-to-plane direction gradually reduces the band gap value. The current-voltage analysis indicates negative differential resistance behavior at room temperature. Besides, high optical conductivity is remarkable for optoelectronic applications. The geometric and electronic structures of bilayer VP, MoS2/VP and bP/VP heterostructures were also revealed. The half-metallic nature of pristine VP is preserved in bilayer form with indirect-to-direct band gap transition in spin down channel, which is an important implication for band gap engineering and practical device applications. The novel VP monolayer system has rich functional properties as a promising 2D material.

The photo response properties of shape memory alloy thin film based photodiode

In this work, the CuAlMn shape memory alloy (SMA) composed as Cu-12.28Al-2.84Mn in wt.% (=72.49Cu-24.70Al-2.81Mn in at.%) was used as a thin Schottky contact layer on an n-Si wafer to produce a Schottky type Al/CuAlMn/n-Si/Al photodiode. To do this, in the first stage of the experimental route, the CuAlMn alloy was prepared in succession by casting in arc melter, homogenizing in β-phase region and lastly by quenching in iced-brine water. Then, the shape memory effect characteristics were revealed by the widely-used thermal (DSC and DTA) and structural (EDS and XRD) characterization tests that been carried out on the alloy. Then, the alloy was thermally evaporated and deposited on the n-Si wafer as a thin film nano layer to make the Al/CuAlMn/n-Si/Al photodiode. The current-voltage (I-V) analysis of the diode taken under dark and different light intensities revealed the rectifying behavior of the diode. The work function value of CuAlMn alloy film was determined as 4.747±0.17 eV. The reverse bias current values of the diode under light were found to be greater than the value observed under dark. The results showed that the diode has a considerable photoconducting feature. The characteristic electrical diode parameters of the junction were computed by using the traditional I-V method. By taking into consideration the literature works related to SMA layered photodiodes, some of the photodiode parameters such as responsivity, photosensitivity, and detectivity, not been reported so far, were determined for the first time. The SMA/n-Si device showed an excellent photosensitivity (~105) performance, and also good merits of responsivity, and detectivity. Which implied that the produced device can be used in various optoelectronic applications. The transient photocurrent (TPC) measurement was performed under the various light intensity conditions and the related characteristic photodiode parameters were determined. Additionally, the capacitance-voltage (C-V) measurement of the SMA-layered photodiode was also carried out at room temperature and different frequencies. The capacitance of the device was observed to be quite sensitive to frequency. Furthermore, a solution suggestion for SMA film cracks and related fractures was also discussed.

Information extraction from Murphy–Good plots of tungsten field electron emitters

This study introduces an easy methodology to test and analyze experimental field electron emission current-voltage data from metallic single-tip emitters; this novel and easy methodology is called the Murphy–Good plots. Tungsten electron emitters were used as an example and were prepared by the electrochemical etching process. The current-voltage characteristics are obtained in high vacuum levels and using a traditional field emission microscope. Murphy–Good plots are used to apply the well-known field electron emission orthodoxy test to the experimental data and then to extract the emitters’ characterization parameters if the test is passed. The novelty in using this type of plots lies in its independency on any correction factors, unlike the traditional Fowler–Nordheim and Millikan–Lauritsen plots, in addition to its simple theoretical form. The results are calculated using a simple web tool that applies the field electron emission orthodoxy test to any type of the current-voltage analysis plots and then to extract the characterization parameters of the emitters.

The influence of a dielectric spacer layer on the morphological, optical and electrical properties of self-dewetted silver nanoparticles

ABSTRACT Metal nanoparticles attract the worldwide interest due to their interesting optical and electrical properties, which allow their implementation as promising light scatters in solar cell devices. These nanoparticles exhibit localized surface plasmon resonance (LSPR) characteristics, which are strongly dependent on both intrinsic and extrinsic factors. Tuning the LSPR characteristics yields to interesting properties in terms of enhancement, localization and guiding of the electromagnetic field on sub-wavelength scales. For that purpose, we investigate in this work the effect of dielectric spacer layer (tin oxide) with different thickness on light reflection due to random self-assembled Ag-NPs. A correlation between morphological properties, optical reflectance and electrical characteristics is established by combining scanning electron microscopy, UV-Vis-NIR spectroscopy and current–voltage analyses. Our results show that a dielectric layer with an appropriate thickness and refractive index is useful for reducing the amount of reflected light and consequently the shifted photocurrent response for all wavelengths.

Modeling and Validation of Passive Rectifier for Airplanes with Variable Frequency and Bipolar DC Buses

Traditional airplanes with fixed frequency and unipolar DC bus (270 V) commonly use 12-pulse passive rectifiers. The increase of power demand and the concern with aircraft efficiency boost the electrification of airplanes using variable frequency (360-800 Hz) and bipolar DC buses (± 270 V). Thus, this paper analyses the 12-pulse passive rectifiers in this new scenario. It is proposed an accurate model, describing its design, to verify if passive rectifiers are suitable for aircraft application complying with current standards. The analysis of the 12-pulse rectifier is done by an association of two 6-pulse rectifiers and considering both sorts of an input filter, L and LC. The mathematical model is presented and considers typical harmonic components, allowing precise analysis of input current and output voltage. Simulation and experimental results are provided to validate the mathematical model. The paper shows that the 12-pulse passive rectifier is not a viable solution when operating under variable frequency, which was verified by the violation of the electricity quality standards.

Graphene oxide nanocomposite with Co and Fe doped LaCrO3 perovskite active under solar light irradiation for the enhanced degradation of crystal violet dye

Pristine LaCrO3 and Co, Fe co-doped La1-xCoxCr1-yFeyO3 (x, y = 0.24) perovskite nanoparticles was prepared via micro-emulsion method and the La1-xCoxCr1−yFeyO3 composite was prepared with 5% reduced-graphene oxide (r-GO) by ultra-sonication process. The morphological, structural and thermal properties were investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The effect of Co, Fe doping and r-GO on the conductivity of the synthesized samples was investigated by current-voltage (I-V) analysis. The perovskite structure was orthorhombic with particle size in 21.24 to 31.58 nm range. Crystal violet (CV) dye was selected for evaluation of photocatalytic activity (PCA) of the prepared materials under visible light irradiation. La1-xCoxCr1-yFeyO3/r-GO showed remarkably higher PCA as compared to pristine LaCrO3 and La1-xCoxCr1-yFeyO3. The r-GO composite furnished the CV dye degradation of 89.08% within 100 min irradiation under visible light at the light intensity in the range of 864.45–872.86 W/m2. This valuable enhancement in PCA was due to the structural features of La1-xCoxCr1-yFeyO3/r-GO nanocomposite. In view of promising PCA, the composite has potential for the catalytic degradation of dyes in effluents using sunlight irradiation.

Electrical properties of inhomogeneous tungsten carbide Schottky barrier on 4H-SiC

In this paper, the electrical behavior of tungsten carbide (WC) Schottky barrier on 4H-SiC was investigated. First, a statistical current-voltage (I–V) analysis in forward bias, performed on a set of equivalent diodes, showed a symmetric Gaussian-like distribution of the barrier heights after annealing at 700 °C, where a low Schottky barrier height (ΦB = 1.05 eV) and an ideality factor n = 1.06 were measured. The low value of the barrier height makes such a WC contact an interesting candidate to reduce the conduction losses in 4H-SiC Schottky diodes. A deeper characterization has been carried out, by monitoring the temperature dependence of the I–V characteristics and the behavior of the relevant parameters ΦB and n. The increase of the barrier height and decrease of the ideality factor with increasing temperature indicated a lateral inhomogeneity of the WC/4H-SiC Schottky contact, which was described by invoking Tung’s model. Interestingly, the temperature dependence of the leakage current under reverse bias could be described by considering in the thermionic field emission model the temperature dependent barrier height related to the inhomogeneity. These results can be useful to predict the behavior of WC/4H-SiC Schottky diodes under operative conditions.

A Device Model for Rb-Conditioned Chalcopyrite Solar Cells

We present a comprehensive device model for Cu(In,Ga)Se $_{2}$ (CIGSe) thin-film solar cells based on numerical SCAPS-1D simulations. The model reproduces the experimentally determined current-voltage and capacitance-voltage characteristics of a Rb-free reference device, a sample that underwent an RbF-treatment, and a sample based on a CIGSe/RbInSe $_{2}$ -stack. According to this model, and in agreement with experimental findings, the main consequences of both Rb-conditionings are an increased doping-density and a defect passivation in the CIGSe as well as the formation of a photocurrent barrier at the hetero interface. With the numerical model established, fundamental aspects of the Rb-conditioning, e.g., the differentiation between its effect on bulk and interface recombination are discussed. Additionally, temperature dependent current-voltage analysis is employed in order to test the model's predictions regarding the interaction of Rb with an injection-current barrier at the back contact of the device. Both the simulation and the temperature dependent current-voltage measurements lead to the result that the RbF-PDT is increasing the height of this barrier, while the deposition of RbInSe $_{2}$ is decreasing it.

Electron transport in C3N monolayer: DFT analysis of volatile organic compound sensing

The sensitivity of Volatile Organic Compounds (VOCs) (methanol, ethanol, isopropanol, and isobutanol) on the surface of two dimensional (2D) nitrogenated graphene (C3N) sheet, has been investigated using density functional theory (DFT) and non-equilibrium Green’s function (NEGF) based ab-initio approach. The effect of adsorption of these organic compounds over C3N surface has been analysed by considering the variations in electronic band structure, density of states, charge transfer and current-voltage analysis. The consequence of adsorption of methanol, ethanol, acetone, isopropanol, and isobutanol shows the variation in electronic and transport properties, hence its sensitivity. The study confirms that the C3N sheet is relatively better sensor for acetone as well as isopropanol, measured with 71% and 59.51% sensitivity, respectively, in comparison to the other considered volatile organic compounds.

Sol-electrophoretic deposition of TiO2 nanoparticle/nanorod array for photoanode of dye-sensitized solar cell

In this investigation, we represent the role of titania (TiO2) nanorod arrays (NRAs) in enhancing the efficiency of dye-sensitized solar cells (DSSCs). Synthesizing TiO2 NRAs via sol-electrophoretic deposition (EPD) by utilizing anodized aluminum oxide (AAO) nanochannel patterns results in one-dimensional morphology of NRAs, confirmed by field emission scanning electron microscope (FESEM) images. Furthermore, a thorough study is performed to clarify every step of NRAs formation from AAO role to reach the best number of deposited layers and a stable morphology. In this way, energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and current-time (J-t) graphs help clarifying this section. To explicate the role of NRAs in boosting the DSSC efficiency, three layers of deposited TiO2 nanoparticles (NPs) using TiO2 sol by the EPD method is compared with a similar sample but consisting of NRAs (nanorod-nanoparticle, NR-NP). Current-voltage (J-V) and electrochemical impedance spectroscopy (EIS) analyses are employed and photovoltaic parameters show NRAs could increase the efficiency of DSSC more than two times from 1.49% (for NP sample) to 3.37% (for NR-NP sample). In addition, EIS results reveal a great drop in TiO2 resistance from 232.2 Ω to 45.13 Ω, indicating the efficient role of NRAs addition in improving the charge transport.

Defect states influencing hysteresis and performance of perovskite solar cells

Here we explore the origin of hysteresis behavior in perovskite solar cells by investigating the defects density of states. In order to reveal this anomalous characteristic, low-temperature capacitance spectroscopy and current-voltage analysis are performed. The present study shows that the open-circuit voltage and hysteresis tend to decrease as the temperature falls below ~200 K. For temperature range of ~300 K to ~180 K, the hysteresis index under dark condition remains almost unaltered whereas, under illuminated condition, the hysteresis index increases with a decrease in temperature. The average hysteresis index under the dark and illuminated conditions is ~71% and ~18% in the tetragonal phase, whereas it becomes ~4% and ~24% in the orthorhombic phase, respectively. Further, below ~180 K, both hysteresis index decreases mutually with the identical rate with a decrease in temperature. Two inflection points have been observed in forward and reverse current cross over-voltage points, indicating rearrangement of internal built-in field distribution and defects at different temperatures. In the tetragonal phase, the Gaussian profile of defect density extends towards lower energy as temperature decreases that refer to a shift in quasi-Fermi level which changed the open-circuit voltage. The increased distribution defect leads to unfavorable accumulation of mobile ions at the electrode and grain boundaries interfaces lead to hysteresis effect in the device.

Investigation of hysteresis in hole transport layer free metal halide perovskites cells under dark conditions

Recent research is a testimony to the fact that perovskite material based solar cells are most efficient since they exhibit high power conversion efficiency and low cost of fabrication. Various perovskite materials display hysteresis in their current-voltage characteristic which accounts for memory behaviour. In this paper, we demonstrate efficient non-volatile memory devices based on hybrid organic-inorganic perovskite (CH3NH3PbI3) as a resistive switching layer on a Glass/Indium Tin Oxide (ITO) substrate. Our perovskite solar cells have been developed over the fully solution processed electron transport layer (ETL) which is a combination of SnO2 and mesoporous (m)-TiO2 scaffold layers. Hysteresis behaviour was observed in the current-voltage analysis achieving high ratio of ON & OFF current under dark and ambient conditions. Proposed perovskite-based Glass/ITO/SnO2/m-TiO2/CH3NH3PbI3/Au device has a hole transport layer (HTL) free structure, which is mainly responsible for a large ratio of ON & OFF current. The presence of voids in the scaffold m-TiO2 layer are also accountable for increasing electron/hole path length which escalates the recombination rate at the surface of the ETL/perovskite interface resulting in large hysteresis in the I–V curve. This memristor device operates at a low energy due to SnO2 layer’s higher electron mobility and wide energy band gap. Our experimental results also show the dependency of voltage scan range & rate of scanning on the hysteresis behaviour in dark conditions. This memristive behaviour of the proposed device depicts drift in hysteresis loop with respect to the number of cycles, which would have a significant impact in neuromorphic applications. Moreover, due to the identical fabrication process of the proposed perovskite-based memristor device and perovskite solar cells, this device could be integrated inside a photovoltaic array to work as a power-on-chip device, where generation and computation could be possible on the same substrate for memory and neuromorphic applications.

Current–voltage analyses of Graphene-based structure onto Al2O3/p-Si using various methods

The present study's main purpose is to determine the current-voltage (I–V) performance of Graphene (Gr) based hetero nanostructure produced on Al2O3/p-Si. Graphene synthesis was carried out using the chemical vapor deposition (CVD) technique on Copper (Cu) foils used as a metal catalyst and transferred onto Al2O3/p-Si using the conventional transfer method. The I–V characteristics of this structure were measured in the dark environment, and the electrical properties of the Gr/Si structure were characterized at room temperature. The rectifying ratio (RR) of the structure was found to be about 103 at ± 3 V. The electrical properties of ideality factor (n), series resistance (Rs), and barrier height (Φb) were examined by using the theory of Thermionic Emission (TE), Norde's method, and Cheung's method. The values of Φb, which were calculated using Norde's method, Cheung's method, and the theory of thermionic emission (TE), were found to be 0.69 eV, 0.71 eV, and 0.68 eV, respectively. The ideality factor was found to be approximately 3.89 according to the theory of TE. The values of series resistance were also determined using the Norde's method and Cheung's two different parameters (dV/dln(I) and H(I)) found to be 9.60 kΩ, 9.12 kΩ, and 5.94 kΩ, respectively.

Band structure and electronic transport across Ta2O5/Nb:SrTiO3 interfaces

Resistive switching devices promise significant progress in memory and logic technologies. One of the hurdles toward their practical realization is the high forming voltages required for their initial activation, which may be incompatible with standard microelectronic architectures. This work studies the conduction mechanisms of Ta2O5 layers, one of the most studied materials for memristive devices, in their initial, as-fabricated state (“pre-forming”). By separating this aspect and resolving the current mechanisms, we provide the input that may guide future design of resistive switching devices. For this purpose, Ta2O5 layers were sputtered on conductive Nb:SrTiO3 substrates. Ta2O5/Nb:SrTiO3 structures exhibit diode behavior with an ideality factor of n ≈ 1.3 over four current decades. X-ray photoelectron spectroscopy analysis of the interfacial band offsets reveals a barrier of 1.3 ± 0.3 eV for electrons injected from the semiconductor into Ta2O5. Temperature-dependent current–voltage analysis exhibits rectifying behavior. While several conduction mechanisms produce good fits to the data, comparing the physical parameters of these models to the expected physical parameters led us to conclude that trap-assisted tunneling (TAT) is the most likely conduction mechanism. Fitting the data using a recent TAT model and with the barrier that was measured by spectroscopy fully captures the temperature dependence, further validating this conduction mechanism.

Triazole-coumarin centered star-shaped polymer: Structural characterizations and electrical properties of graphene composites

In present study, new three-arm initiator containing coumarin group and new 4-(3-(4-methoxyphenyl)acryloyl) phenyl acrylate (MPAC) was synthesized. Three-armed star-shaped polymer was obtained by polymerization using ATRP method from the chlorine ends of the initiator. The structure characterization was performed by FT-IR, 1H-NMR, 13C-NMR spectroscopy techniques. Thermal analyzes were performed by using thermogravimetry (TGA) and differential scanning calorimetry analysis (DSC) techniques in a nitrogen atmosphere. Thermal decomposition activation energy (Ea) of star polymer was determined by the Flynn-Wall-Ozawa and Kissinger methods. The average activation energy in the range of 0.02-0.3 conversion range was determined as 115.28 kJ/mol and 152.72 kJ/mol, respectively. Polymer composites were prepared by adding graphene particles in different ratios (0.5%, 1.0%, 2.0%, and 4.0% by weight) to the polymer matrix. The dielectric properties of star polymer and graphene composites were investigated in a range of 100 Hz-20 kHz frequency. Besides, the dielectric properties of the pure polymer were examined as a function of frequency at different temperatures (25 °C, 40 °C, 55 °C, 70 °C,). Furthermore, the polymer/4% graphene composite/p-Si thin-film heterojunction diode properties were investigated using current-voltage (I-V) analysis at room temperature in dark. The electrical parameters of heterojunction diode such as the rectification ratio (RR), barrier height (Φb) and ideality factor (n) were investigated. The frequency dependence of capacitance and the role of interface states were examined. The results showed that chalcone substituted three-arm star polymer/4% graphene composite has a diode and capacitor characteristic.

Enhancement of Solar Cell Performance of Electrodeposited Ti/n-Cu2O/p-Cu2O/Au Homojunction Solar Cells by Interface and Surface Modification

Cuprous oxide (Cu2O) homojunction thin films on Ti substrates were fabricated by an electrochemical deposition in which a p-Cu2O layer was deposited on an n-Cu2O layer by carefully controlled bath conditions. It was found that the open-circuit voltage of the homojunction solar cell was significantly influenced by the pH of the lactate bath. The variation of the pH was used to achieve the best possible crystal orientation for homojunctions. The crystallinity and morphology of the products were characterized by X-ray diffraction (XRD), high-energy x-ray diffraction (HEXRD), and scanning electron microscopy (SEM). The current density voltage (J-V) analysis showed that the sulfur treatment and annealing enhanced the photocurrent by ten-fold compared to the untreated and unannealed homojunction solar cell. X-ray photoelectron spectroscopy (XPS) studies confirmed that the sulfur treatment eliminated the surface CuO and formed a thin layer of CuS, which was very useful to make the front Ohmic contact. Transient measurements confirmed that the p-type Cu2O layer, which was subjected to sulfur treatment, significantly reduced the recombination, thus enhancing the efficiency of the solar cell. The best sulfur treated annealed Ti/n-Cu2O/p-Cu2O/Au solar cell produced an energy conversion efficiency of 2.64% with an open-circuit voltage of 490 mV and a short circuit current density of 12.8 mA cm−2 under AM 1.5 illumination.

Investigation on the Trap Signature in Organic Semiconductor Turmeric Film Through Current–Voltage Analysis

The analytical description of the trap signature in the charge conduction process of turmeric dye-based organic semiconductor has been presented in this study. An analytical explanation of the built-in potential Vx–V graph that emphasizes the presence of trapping states has been provided. Differential analysis of current–voltage (I–V) characteristics has also been conducted to verify the trap signature of the carrier in the device. The non-monotonous decrement of the G(V)–V plot verifies the trap signature. The values of trap energy (Et) and trap factor ( $$ \theta $$ ) have been derived from the logarithmic I–V relationship. From the analysis of the semilogarithmic I–V plot, the barrier height (ϕbi) of the device has also been determined. The overall I–V curve has been taken into account to examine the Richardson–Schottky and Poole–Frenkel effects on the trap-assisted charge conduction process. From the results of the experiment, the Schottky effect has been observed to be effective, which leads to a bulk-limited charge conduction process.

Failure analysis of field‐failed bypass diodes

AbstractDefective bypass diodes are often found as the largest factor leading to power loss in solar modules. Here, we report on failure mechanisms by investigating shunted bypass diodes from a rooftop installation, using a combination of multiple characterizations including current–voltage analysis, thermal‐runaway testing, X‐ray computed tomography, lock‐in thermography, focused ion‐beam cross‐section imaging, chemical decapsulation, optical microscopy, and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy. Differing from static discharge typically associated with lightning strikes on modules, we found diode failure by the mechanism of thermal damage under continuous, long‐term overstress in forward bias. Our conclusion is based on evidence of energy dissipated—the small to medium extent of melt‐through on the Schottky diode face. The diode failure shows distortions or roughening of the Schottky diode metal‐semiconductor interface with the die attach, and some failures are accompanied by die‐attach solder melting. We propose that nonuniform irradiance on the modules caused diode shunting due to extended periods of heat dissipation in the modules, because modules in this string were placed in two different orientations. In contrast, a second parallel module string of the same module type on the same rooftop with a unique plane of array did not show any diode failures. The thermal damage failure of melt‐through was caused by the long‐term current generated by overstressing of diodes that may have had crystalline and impurity defects.

Luminescence effects on subcell current–voltage analysis in InGaP/GaAs tandem solar cells

We investigate the role of luminescence effects on the analysis of solar cell properties. InGaP/GaAs tandem solar cells fabricated using hydride vapor phase epitaxy have a luminescent coupling (LC) efficiency of 0.6% from the top to the bottom subcell. We investigate the impact of LC on subcell current–voltage curve analysis using electroluminescence (EL) measurements. EL efficiency measurements were performed using a reference InGaP single-junction device. It was found that the luminescence extraction from the top subcell, and therefore its luminescence collection efficiency, is lower than that from the bottom subcell. This is due to LC from the top subcell to the bottom subcell. By considering the luminescence extractions of each subcell, more reasonable subcell voltages than those found by conventional methods can be obtained.

Electrical and photovoltaic properties of p-n heterojunctions obtained using sol gel derived nanostructured ZnO:La films onto p-Si

Abstract The p-Si/n-ZnO:La heterojunctions were obtained using different dopant levels (0.2, 0.4, 0.6, 0.8 and 1%) nanostructured ZnO films. To characterize the electrical behavior of these structures, the current-voltage (I-V) analysis were performed. It was observed that all of them showed good rectifying behavior. The diode parameters were determined by using different methods. To characterize the photovoltaic behavior of these diodes, I-V measurements were performed under illuminations (20–100 mW/cm2). The results indicated that obtained photodiode exhibited a good photoconducting behavior.