Current-voltage Characteristics Research Articles

Investigation of the performance and stability of self-powered polythiophene-based photodiodes under UV and visible light illumination

In this study, we fabricated polythiophene (PTh) and silver-decorated polythiophene (Ag@PTh) films on n-type silicon substrates using the electrochemical deposition method to investigate their electrical and photoelectrical properties in metal/interlayer/n-Si heterostructures under various conditions. The physical properties of the films were comprehensively investigated through UV-Vis, Raman, XPS and SEM analysis. The results from these analyses confirmed the successful deposition and formation of the films on the n-Si substrates. Additionally, a comparison of the current-voltage (I-V) characteristics of the PTh/n-Si and Ag@PTh/n-Si devices was conducted under both dark conditions and illumination with visible and UV light. While both devices exhibited typical rectifying diode behavior, the Ag@PTh/n-Si device demonstrated greater rectification with a RR of 2.49 x 105 at ± 2 V under dark conditions. In addition, the Ag@PTh/n-Si device, with self-powered property, displayed notably enhanced performance metrics, including a significantly higher ON/OFF ratio, responsivity, and detectivity, particularly evident under UV light illumination when compared to white light. Furthermore, to assess the long-term reliability of these devices, stability tests were conducted by repeating the I-V measurements after 90 days under identical conditions. The Ag@PTh/n-Si device exhibited considerably better stability over time than the PTh/n-Si device, maintaining consistent performance without notable degradation. So, in light of the findings, it can be concluded that the Ag@PTh/n-Si device has substantial potential for advancing optoelectronic technology.

Bismuth oxyiodide as a highly efficient room temperature NOx gas sensor: Role of surface orientations on sensing performance

In the pursuit of developing fast and reliable gas sensors, a new ternary oxide semiconductor, a bismuth oxyiodide (BiOI)-based sensing material, has been reported with desirable adsorption energy, short recovery time, and high sensitivity and selectivity for detecting nitrogen oxide mixtures (NOx, typically NO and NO2). The structural, electronic, and transport properties of both (001) and (012) planes of BiOI surfaces upon the adsorption of six environmentally relevant gases (NO, NO2, SO2, SO3, O2, and H2O) are systematically explored using a combination of density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. The results indicate that BiOI (001) exhibits weak interaction with these gases, with the highest adsorption energy observed for NO. In contrast, the BiOI (012) surface shows enhanced adsorption stability for these gases, particularly acceptable strong adsorption to NO2, indicating its promising capability for detecting these gases with high specificity. Moreover, it demonstrates the most intense chemisorption for SO3, suggesting it to be a reliable SO3 adsorbent/cleaner. The obtained transport characteristics, including current-voltage (I-V) and resistance-voltage (R-V) curves, further highlight the higher selectivity of the BiOI (001) device towards NO and the BiOI (012) device towards NO2 against the other gases. Furthermore, the transmission spectra analyses reveal that the BiOI-based sensor can electrically discriminate the target gas molecules from other considered gas molecules. Besides, the practical application possibilities of both orientations are explored by estimating their recovery time, and the results show that the BiOI sensor has excellent recovery times at room temperature (NO/BiOI (001) = 0.158 ns, and NO2/BiOI (012) = 3.89 s), highlighting its potential as an ideal reversible gas-sensing material for detecting NOx gases.

Exploring Nano-optical Molecular Switch Systems for Potential Electronic Devices: Understanding Electric and Electronic Properties through DFT-QTAIM Assembly.

The design and synthesis of molecular nanoswitches using organic molecules represent a crucial research field within molecular electronics. To understand the switching mechanisms, it is essential to investigate various factors, such as charge/energy transfer, electron transfer, nonlinear optical properties (NLO), current-voltage (I-V) curves, Joule-like (LJL) and Peltier-like (LPL) intramolecular phenomenological coefficients, as well as the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) boundary orbitals. In this Article, a novel approach to designing a molecular nanoswitch and understanding its ON/OFF mechanism is presented, utilizing the quantum theory of atoms in molecules (QTAIM), density functional theory (DFT), and Landauer theory (LT). These analyses contribute significantly to a deep understanding of switching effects within molecular electronic systems.

Insight into deposition duration-varied crystallinity, optical parameters, morphology and electrical properties of solution-processed nanostructured CdSSe thin films

Nanostructured cadmium sulpho selenide (CdSSe) films have been grown onto glass substrates for different deposition durations via a facile solution-based method known as chemical bath deposition (CBD). XRD studies revealed that the crystallites in the films possessed hexagonal (wurtzite) structures with predominant orientation along the (002) plane. The crystallite size increased from ∼5.95 nm to ∼16.69 nm with the increase in deposition duration from 1 h to 4 h. The absorbance, transmittance and reflectance measurements were carried out. A transparency of ∼(50–80) % was obtained for the films. The direct optical energy band gap was found to decrease from 1.982 eV to 1.952 eV with the increment of deposition duration from 1 h to 4 h. SEM micrographs of the films revealed the presence of nano spherical-shaped grains with an average size ranging from ∼305 nm to ∼612 nm. HRTEM images illustrated the presence of compact nano-spherical grains and nano-crystallites distributed in random orientations. Raman spectroscopy divulged the presence of CdSe and CdS vibrational Raman modes and overtones in the films. PL spectra revealed a prominent red emission band along with weak luminescent bands in the yellow-red emission region. The presence of Cd–Se and Cd–S bonds in the films was validated using FTIR analysis. Electrical investigation revealed the linear current‒voltage relationship for the films with the rise in conductivity with deposition duration. Hence, deposition duration stands out as a vital parameter for modulating the properties of CdSSe thin films for use in photovoltaic devices and optoelectronics.

Interface Collaborative Strategy for High Mobility Organic Single‐Crystal Field‐Effect Transistors with Ideal Current–Voltage Curves

AbstractThe key roles of electrode/semiconductor and semiconductor/dielectric interfaces play in the ideality of organic field‐effect transistors (OFETs) by traditional device preparation technologies are not yet fully understood, which severely limits progress in the design of molecules, the understanding of transport mechanisms, and the circuit applications of OFETs. Herein, at a quantitative level, the origin of nonideal current–voltage (I–V) curves and possibly overestimated mobility in single‐crystal OFETs is revealed, including contact resistance (Rc), charge trapping, and scattering at interfaces of devices. Impressively, an efficient interface collaborative strategy, which consists of transferred “doped” electrodes with tunable contact “doping” localized regions at the source‐drain contacts and polymer‐modified SiO2 with suitable surface polarity (γsp) is further demonstrated that have great advantages in the construction of ideal high mobility devices. Also, an interesting double‐edged sword effect of γsp of dielectric on the ideality of OFETs is observed. The dielectric with a lower γsp can result in higher mobility, while too low γsp would degrade the device ideality due to significant effect of charge scattering. The findings not only provide new perspectives and strategies to construct ideal OFETs but also offer useful guidance to correctly evaluate organic semiconductor materials.

Diagnostics of the ionization processes in hydrocarbon flame with the use of the current-voltage characteristics

The possibility of estimating the ionization parameters of high-temperature gas mixtures formed as a result of combustion processes is considered on the basis of the current-voltage characteristics measured using electrodes that generate an external electric field in the media under consideration.

Methyl Methacrylate Copolymer with Pendant Thioxanthenone Groups as Active Layer for Resistive Memory Devices.

An electro-active copolymer of methyl methacrylate and 2-((4-acroylpiperazine-1-yl)methyl)-9H-thioxanthene-9-one (poly(MMA-co-ThS)) was synthesized by radical polymerization. The copolymer has good solubility in most organic solvents, thermal stability up to 282 °C and excellent ability to form thin films on silicon wafers. Poly(MMA-co-ThS) films exhibited an electrochemical and electrochromic activity resulting in the formation of long-lived radical anion states of pendant thioxanthone groups inside the film. These states exhibit optical transitions in the visible region as a broad optical absorption band, 500<λ<900 nm (1.38<Wopt(ThS)<2.48 eV) with a maximum at λmax=675 nm (1.84 eV). Using temperature measurements of the current-voltage characteristics of p-Si(100)/poly(MMA-co-ThS)/Al devices, it was shown that the charge transport in the film occurs by a multiphonon mechanism, which is quantitatively described by the Nasyrov-Gritsenko model of phonon-assisted tunneling between traps. The value of the optical transition energy of the trap, determined by the Nasyrov-Gritsenko model, Wopt=1.8 eV, is in a good agreement with Wopt(ThS), confirming the nature of the traps as 9H-thioxanthen-9-one structures. The n++Si(100)/poly(MMA-co-ThS)/Al memory device exhibited a memristive effect (reversible ON/OFF switching of the device) with an initial "forming" cycle followed by repetitive memory cycles characterized by bipolar switching.

Nonlinearities and timescales in neural models of temporal interference stimulation.

In temporal interference (TI) stimulation, neuronal cells react to two interfering sinusoidal electric fields with a slightly different frequency ( , in the range of about 1-4 kHz, in the range of about 1-100 Hz). It has been previously observed that for the same input intensity, the neurons do not react to a purely sinusoidal signal at or . This study seeks a better understanding of the largely unknown mechanisms underlying TI neuromodulation. To this end, single-compartment models are used to simulate computationally the response of neurons to the sinusoidal and TI waveform. This study compares five different neuron models: Hodgkin-Huxley (HH), Frankenhaeuser-Huxley (FH), along with leaky, exponential, and adaptive-exponential integrate-and-fire (IF). It was found that IF models do not entirely reflect the experimental behavior while the HH and FH model did qualitatively replicate the observed neural responses. Changing the time constants and steady state values of the ion gates in the FH model alters the response to both the sinusoidal and TI signal, possibly reducing the firing threshold of the sinusoidal input below that of the TI input. The results show that in the modified (simplified) model, TI stimulation is not qualitatively impacted by nonlinearities in the current-voltage relation. In contrast, ion channels have a significant impact on the neuronal response. This paper offers insights into neuronal biophysics and computational models of TI stimulation.

Advancements in CIGS/ZnS heterojunction solar cells: Experimental and numerical analysis

This study presents a comprehensive experimental investigation conducted on a CIGS-based solar cell incorporating a ZnS buffer layer. The primary objective was to determine key parameters of the CIGS/ZnS heterojunction, including parasitic resistances (Rs and Rsh), ideality factor (n), and barrier height (ϕB), using experimental current-voltage (I-V) characteristics over a temperature range of 150 K to 300 K under dark conditions. The heterojunction was modelled using a single-diode electrical circuit that accounted for parasitic resistances. Two methods were employed for parameter determination: direct analysis of the (I-V) curves and Cheung's method. Additionally, the charge transport mechanism within the heterojunction is investigated and discussed. Furthermore, the performance of the Al:ZnO/i:ZnO/ZnS/CIGS/Mo solar cell was assessed using the SCAPS-1D simulator, demonstrating an initial solar energy conversion efficiency of 15.01 %. To enhance this efficiency, a hole transport layer (HTL) was integrated between the back electrode and the absorber layer. Extensive studies were conducted to optimize the thickness and doping density of the HTL, including a comparative analysis of different materials used as HTLs. These optimizations resulted in a significant increase in conversion efficiency, reaching up to 28.68 %.

Energy consumption model of flow-through electrolyzer considering mass transfer overpotential for hydrogen production from alkaline water splitting

Flow-through electrolyzer can improve the efficiency of hydrogen production from alkaline water splitting and determining the optimal electrolyte velocity through electrode pores is crucial for reducing energy consumption. In this study, an energy consumption model of flow-through electrolyzer considering mass transfer overpotential (Emass) has been developed. The model of Emass due to gas hold-up (ϕ) in the electrolyzer accounts for the density, viscosity, surface tension, linear velocity, and current density. The model-predicted value is in good agreement with the experimental results, which indicated that the increase of velocity effectively reduces ϕ and Emass. Then, Voltage-Current curve models combining reversible voltage, activation overpotential, ohmic overpotential, and Emass are developed. Based on this, an energy consumption model, combining both consumption from electrolyzer and pumps, is established to evaluate the overall energy consumption of hydrogen production. It can be calculated the Emass at 400 mA cm−2, 6 M KOH, 353 K can be reduced from 0.363 V to 0.048 V if the circulation velocity rises from 0.001 m s−1 to 0.1 m s−1. The model predicts that total energy consumption is 4.36 kWh Nm−3 with energy consumption for pump being 0.02 kWh Nm−3 at 400 mA cm−2 and 0.063 m s−1.

Bolometric detection of Josephson radiation.

One of the most promising approaches towards large-scale quantum computation uses devices based on many Josephson junctions. Yet, even today, open questions regarding the single junction remain unsolved, such as the detailed understanding of the quantum phase transitions, the coupling of the Josephson junction to the environment or how to improve the coherence of a superconducting qubit. Here we design and build an engineered on-chip reservoir connected to a Josephson junction that acts as an efficient bolometer for detecting the Josephson radiation under non-equilibrium, that is, biased conditions. The bolometer converts the a.c. Josephson current at microwave frequencies up to about 100 GHz into a temperature rise measured by d.c. thermometry. A circuit model based on realistic parameter values captures both the current-voltage characteristics and the measured power quantitatively. The present experiment demonstrates an efficient, wide-band, thermal detection scheme of microwave photons and provides a sensitive detector of Josephson dynamics beyond the standard conductance measurements.

Hydrophobic modification enhances the microstructure stability of the catalyst layer in alkaline polymer electrolyte fuel cells.

Alkaline polymer electrolyte fuel cells (APEFCs) have achieved notable advancements in peak power density, yet their durability during long-term operation remains a significant challenge. It has been recognized that increasing the hydrophobicity of the catalyst layer can effectively alleviate the performance degradation. However, a microscopic view of how hydrophobicity contributes to the stability of the catalyst layer microstructure is not clear. Here, we construct a membrane electrode assembly (MEA) with enhanced structural stability and durability by incorporating polytetrafluoroethylene (PTFE) particles into the catalyst layer. MEAs modified by this approach exhibit stabilized voltage platforms in current step tests and reduced hysteresis in current-voltage polarization curves during operation, indicating the critical role of PTFE in the removal of the excess water within the catalyst layer. Fuel cells with PTFE modification show more than 45% increase in electrochemical durability. By characterizing with field-emission scanning electron microscopy (FE-SEM) the surface and the internal microstructures of MEAs after durability tests, we find that the catalyst layers modified by PTFE experience much less reduction in porosity and less agglomeration of the solid components. These findings elucidate the microscopic mechanisms by which hydrophobicity promotes a more stable catalyst layer structure, thereby enhancing the durability of APEFCs. This research advances our understanding of hydrophobicity's impact on catalyst layer stability and offers a practical method to enhance the durability of APEFCs.

Annealing Effect on Structural, Optical and Electrophysical Properties of ZnSe Nanocrystals Synthesized into SiO2/Si Ion Track Template.

We report the results of synthesis of zinc selenide (ZnSe) nanocrystals into SiO2/Si track templates formed by irradiation with 200 MeV Xe ions up to a fluence of 107 ions/cm2. Zinc selenide nanocrystals were obtained by chemical deposition from the alkaline aqueous solution. Scanning electron microscopy, X-ray diffractometry, Raman and photoluminescence spectroscopy, and electrical measurements were used for characterization of synthesized ZnSe/SiO2nanoporous/Si nanocomposites. XRD data for as-deposited precipitates revealed the formation of ZnSe nanocrystals with cubic crystal structure, spatial syngony F-43m (216). According to non-empirical calculations using GGA-PBE and HSE06 functionals, ZnSe crystal is a direct-zone crystal with a minimum bandgap width of 2.36 eV and anisotropic electronic distribution. It was found that a thermal treatment of synthesized nanocomposites at 800 °C results in an increase in ZnSe nanocrystallites size as well as an increase in emission intensity of created precipitates in a broad UV-VIS spectra range. However, vacuum conditions of annealing still do not completely prevent the oxidation of zinc selenide, and a formation of hexagonal ZnO phase is registered in the annealed samples. The current-voltage characteristics of the synthesized nanocomposites proved to have n-type conductivity, as well as increased conductivity after annealing.

Comparative study of Ti/Al and Ti/Al/Ti/Au ohmic contacts to AlGaN/GaN heterostructures

We investigated the electrical properties and the ohmic contact formation considering Ti/Al and Ti/Al/Ti/Au ohmic contact metallization schemes on AlGaN/GaN heterostructures. The specific contact resistance of contacts was determined by characterizing the current–voltage relation from TLM measurement. The lowest value for the specific contact resistivity was obtained using Ti/Al/Ti/Au metallization. An interfacial TiN layer was monitored at the contact-AlGaN interface. TiN phases were found at both contacts, but the thickness in the Ti/Al/Ti/Au contact reached 8 nm, while the thickness in Ti/Al was thinner and discontinuous. The surface roughness of the Ti/Al/Ti/Au contact was determined as 8.17 nm and that of the Ti/Al contact as 36.23 nm. It was found that the spesific contact resistance depends on the atomic structure of the metal–semiconductor interface and composition and structure of the ohmic contact layers. These results showed that it is possible to achieve higher reliability and uniformity as well as lower contact resistance in AlGaN/GaN HEMTs with Ti/Al/Ti/Au contact compared to Ti/Al contact.

Investigating the role of Ag-doped ZnO thin films in UV photodetectors produced via laser assisted chemical bath growth technique

This study introduces the innovative fabrication of Ag-doped ZnO thin films (AgxZnO(100−x) TFs) with varying silver (Ag) concentrations (x) of 0.5, 1.0, 1.5, and 2.0 at% on glass substrates using a simple and cost-effective method known as laser-assisted chemical bath growth (LACBG). This process aims to create metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors. A continuous wave semiconductor laser with a 444.5 nm wavelength, 5 W power, and 6 min irradiation time was employed to synthesize high-quality Ag-doped ZnO TFs on the glass substrate. Ag electrodes were utilized as Schottky contacts to form MSM UV photodetectors. Structural and morphological analyses conducted using XRD and SEM revealed vertically aligned nanorods and nanoflowers with a high c-axis orientation and hexagonal wurtzite facets, while EDX confirmed Ag incorporation into the ZnO lattice. The UV–Visible absorbance spectra indicated a decrease in bandgap from 3.28 to 2.84 eV with increased Ag content. The current-voltage (I–V) characteristics of the Ag-doped ZnO TFs UV photodetector showed significantly enhanced conductivity at a 2.0 at% concentration level, achieving a responsivity of 10.78 A/W, an external quantum efficiency of 34.67 % at −3 V bias voltage. Finally, the modified device exhibited a sensitivity of 14661.9 %, a gain of 147.62, and a detectivity of 2.25 ×107 Jones, demonstrating its suitability for optoelectronic applications.

Optimization of self-rectifying analog memristors by insertion of an interfacial layer

Self-rectifying analog memristors have emerged as promising components for neuromorphic computing systems due to their inherent rectifying behavior and analog resistance states. Among these devices, BiFeO3 (BFO) memristors have shown exceptional performance, attributed to the accumulation and migration of oxygen vacancy (Vo··). However, the movement of Vo·· within the structure of the device presents challenges in optimizing their performance. To address this, the insertion of an interfacial layer has been proposed as a strategy to change the movement of Vo·· and enhance the behavior of memristor. In this study, we investigate the optimization of self-rectifying analog memristors by inserting an interfacial layer in BFO memristors. The more significant nonlinearity in high resistance state branch we observed in the current–voltage relationship leads to better rectifying behavior and a larger on/off ratio at room temperature, which indicates that the interfacial layer improves rectifying behavior. Moreover, we propose a model based on the modulation of the interfacial barrier to elucidate the impact of the interfacial layer on the BFO memristor. These findings provide insight into the design principles for optimizing self-rectifying analog memristors, with potential applications in neuromorphic computing.

Analysis and experimental verification of two types of three‐coil MCR‐WPT system with constant current and constant voltage characteristics

Analysis and experimental verification of two types of three‐coil MCR‐WPT system with constant current and constant voltage characteristics

Improved high temperature energy storage density and efficiency of polyimide nanocomposites via hindering charge and molecular motions

Electric vehicles and renewable energy consumption have huge demands for high-performance polymer dielectric capacitors. However, the resistivity and breakdown strength of existing polymer dielectrics deteriorate significantly at high temperatures, reducing the energy storage density and charge-discharge efficiency of capacitors below service requirements. The charge transport and molecular chain motion characteristics in linear polymers determine their conductivity, breakdown, and energy storage properties, but the quantitative relationship between them is not clear. An in-situ polymerization method was used to prepare polyimide/Al2O3 nanocomposites (PI/Al2O3 PNCs). Experimental results show that the resistivity, breakdown strength, energy storage density, and charge-discharge efficiency of PNCs increase initially and then decrease with increasing doping content, peaking at 3 wt%. The discharged energy density of PI/Al2O3-3 wt% PNCs at 180°C is 207.52 % higher than pure PI. A conductance-breakdown-energy storage co-simulation model based on charge transport and molecular chain displacement was used to simulate the voltage-current, breakdown, and energy storage characteristics of PNCs. The simulation results are consistent with the experiments. Comparative studies between simulation and experiments show that the independent interface zone between nanofillers and PI hinders charge transport and molecular chain movement, reducing electric field distortion and molecular chain spacing, thereby improving high-temperature breakdown and energy storage performance of PNCs.

Optimization of electron transmission on a 1D lattice

Finding optimal multi-layer heterostructure configurations that result in desired current–voltage characteristics requires physical control of electron scattering processes. It is shown how a one-dimensional tight-binding Hamiltonian combined with the adjoint method may be employed to explore this non-convex and non-intuitive design space. Such optimal parameter exploration has application to study of vertical electron transport through van der Waals stacked few-layer quantum materials and nano-scale single-crystal semiconductor heterostructures.

Effect of nitrogen content on the structure and superconductivity of reactive sputtered NbTiN thin films

In this research, we have studied the structural and electrical properties of NbTiN films deposited on MgO and SiO2/Si substrates by reactive dc sputtering. The formation of stoichiometric NbTiN is very sensitive to N concentration and can be easily adjusted by changing the discharge current and Ar: N2 ratio along the current–voltage curves (IVCs) of the NbTi target. Excessive or insufficient N concentration in NbTiN leads to sublattice expansion or distortion, resulting in a decrease in critical temperature T c. At Ar: N2 ratio of 30:4 and discharge current of 2.2 A, T c as high as 15.8 K and 15.3 K has been obtained for 200 nm thick NbTiN/MgO and NbTiN/SiO2/Si samples, respectively. In addition, the critical density J c of the 4 μm-wide and 7 nm-thick NbTiN film grown on MgO substrate at 2 K reaches 19.2 MA cm−2, which is approximately twice as high as the 10.9 MA cm−2 of the same-sized NbTiN film grown on SiO2/Si substrate. Therefore, by further fine-tuning the N concentration in combination with the IVCs of the target, high-quality stoichiometric NbTiN can be obtained.