Including Current Voltage Research Articles

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.

A Scalable Knowledge-Based Neural Network Model for GaN HEMTs With Accurate Trapping and Self-Heating Effects Characterization

In this article, a scalable knowledge-based neural network (KBNN) large-signal model of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) with accurate trapping and self-heating effects characterization is developed. An improved empirical drain current model is proposed and added to the neural network as prior knowledge, thereby establishing the drain current model, including self-heating effect. A new empirical equation is proposed to model the buffer-related trapping effect more accurately. Taking Angelov capacitance models as prior knowledge, the KBNN capacitance models are completed. Moreover, the scaling characteristics of the proposed KBNN model are studied. The developed model has been fully verified by different sizes of GaN HEMTs. Good agreement between the model simulation results and the measurement data, including current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$</tex-math> </inline-formula> ), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula> -parameters, power characteristics, and load-pull data, confirms the effectiveness of the proposed model. The proposed scalable KBNN model is fast and accurate and would be useful for accurate large-signal modeling of large gate periphery GaN HEMTs for high-power radio frequency (RF) applications.

The influences of shielding gas and quartz tube on discharge properties and reactive species productions of nanosecond pulsed gas–liquid discharge

In this paper, shielding gas (He) and shielding quartz tube (straight tube and conical tube) is added to nanosecond pulsed He gas–liquid discharge (G-LD) to limit the air diffusion into plasma, and for the purposes of enhancing the plasma volume and productions of ċOH and H2O2. The plasma properties, including current–voltage waveforms, the temporal-resolved discharge images, optical emission spectra, gas temperature, electron density, and the ċOH and H2O2 productions are analyzed and compared among different discharges generated under the cases of no shielding, shielding He gas, shielding straight tube, and shielding conical tube. The results show that adding extra shielding gas and tubes in the discharge reactor can decrease the gas temperature and electron density, but enhance the plasma volume and area of plasma-liquid interface in comparison with no shielding case. Besides, the addition of shielding gas has the most benefit for enhancing the productions of ċOH and H2O2 produced by G-LD. Adding a shielding conical tube slows down the decrease extent of ċOH and H2O2 productions caused by increasing discharge gap. When the discharge gap excesses 6 mm, adding a shielding conical quartz also has an obvious increase effect on the production of ċOH and H2O2 in compared with no shielding case. While adding a shielding straight tube with small diameter has a little effect on H2O2 production, even a negative effect on ċOH production.

Printed silver contacts for Cd[formula omitted]Zn[formula omitted]Te radiation detectors

In this work, we evaluate a novel jetink printing method with silver nano particle ink for fabrication of metal–semiconductor–metal structures based on Cd1−xZnxTe for gamma-ray detector applications. Contact printing technology offers several advantages in terms of infrastructure and prototype cycle time. For comparison and reference similar samples with thermally evaporated silver and indium contacts were processed and analyzed. The MSM devices were investigated by various static and dynamic characterization methods including current–voltage (I–V), power spectral density of noise (PSD), transient current technique (TCT), and gamma-spectroscopy. In addition, impact of thermal annealing up to 200 °C was studied. The devices with the printed contacts exhibit comparable performance with the reference benchmark detectors. Preliminary study indicate that the printed contacts are immune to moderate thermal treatment, and moreover, show signs of improvement with annealing.

Investigation on the current conduction mechanism of HfZrOx ferroelectric memory

HfZrOx (HZO)-based materials have received much attention due to their special film characteristics in recent years. Ferroelectric random access memory (FeRAM) based on this HZO material also has promising potential as a next generation memory due to its non-volatile characteristics, excellent endurance, and low power consumption. Previous research has mainly focused on the material properties of HZO-based FeRAM. However, an in-depth investigation of the electrical properties of HZO-based FeRAM is necessary to better understand its transporting mechanism. In this contribution, this study aims to investigate the mechanism of an HZO-based metal–ferroelectric-metal capacitor using comprehensive experimental results, including current–voltage, capacitance–voltage, and polarization–voltage measurements. Experiments at various temperatures are also conducted to help verify the transport mechanism. The low current transport by the Fowler–Nordheim tunneling mechanism does not change with temperature, whereas the high current transport via the Schottky mechanism increases with increasing temperature. We found that the orientation of the dipole plays an important role. Finally, we also propose a band model to explain the electron transport in this HZO-based FeRAM.

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.

Influence of Size on Optical and Electrical Properties of GaN-Based Membrane μ-LED.

The electrical and optical properties of micro-light emitting diodes (μ-LEDs), including current-voltage (I-V), capacitance-voltage (C-V) curves, photoluminescence (PL) as well as electroluminescence (EL) spectra have been measured and analyzed. It is found that the unit area emitting intensity of small size μ-LED is stronger that of big size μ-LED at the same conditions, due to the enhancement of both the internal quantum efficiency ηint and extraction efficiency Cex. The present method of utilizing the μ-LED for improving the unit area brightness of LEDs is applicable to high efficiency surface emitting device on GaN-on-silicon platform.

Memristors Based on Poly(p-xylylene) with Embedded Silver Nanoparticles

The properties of memristors based on poly(p-xylylene) with embedded silver nanoparticles have been studied, including current–voltage characteristics, resistive switching phenomenon, stability with respect to multiple switching cycles, and ability to store the resistive state in time. It is established that the incorporation of silver nanoparticles into polymer matrix significantly improves the main characteristics of memristors. The obtained results can be used for the creation of large memristor arrays with homogeneous characteristics capable of emulating synapses in neuromorphic computing systems.

Exploration of the impact of interface states density on the specific contact resistivity in TiSix/n+-Si Ohmic contacts through high-low frequency method

In our previous work, a reduction of specific contact resistivity (ρc) in TiSix/n+-Si Ohmic contacts by ∼21% has been achieved with proper Ge Pre-amorphization Implantation (PAI). In this work, the mechanism behind such an improvement using Ge PAI is explored experimentally. Versatile characterizations including current–voltage (I–V), capacitance–voltage (C–V) measurements and cross-sectional transmission electron microscopy (XTEM) are performed and analyzed. High-low frequency method is used to extract the responsive interface states density (Dit) of TiSix/n-Si Schottky diodes with and without Ge PAI. It is demonstrated that in TiSix/n+-Si Ohmic contacts, the ρc reduction by ∼21% with Ge PAI should be ascribed to the reduction of Dit at TiSix/n-Si interface. From the distribution of Dit, it can be inferred that a part of shallow level defects can be annihilated after annealing for TiSix/n-Si with Ge PAI, but deep level traps still exist. A further discussion about the relationship between Dit and ρc is tentatively provided.

Anisotropic Negative Differential Resistance in Monolayer Black Phosphorus

The tremendous potential application in emerging two-dimensional layered materials such as black phosphorus (BP) has attracted great attention as nanoscale devices. In this paper, the effect of anisotropic negative differential resistance (NDR) in monolayer black phosphorus field-effect transistors (FETs) is reported by the first-principles computational study based on the non-equilibrium Green’s function approach combined with density functional theory. The transport properties including current-voltage (I-V) relation and transmission spectrum of monolayer BP are investigated at different gate voltages (Vg). Further studies indicate that NDR occurs at a specific gate voltage in the armchair direction rather than in the zigzag direction. The decrease of current in I-V characteristics can be understood from the generation of non-conducting states region moving towards the Fermi level resulting in a reduction of the integration within corresponding energy range in the transmission spectrum. Our results offer useful guidance for designing FETs and other potential applications in nanoelectronic devices based on BP.

10 μ m-thick four-quadrant transmissive silicon photodiodes for beam position monitor application: electrical characterization and gamma irradiation effects

Silicon photodiodes are very useful devices as X-ray beam monitors in synchrotron radiation beamlines. Owing to Si absorption, devices thinner than 10 μ m are needed to achieve transmission over 90% for energies above 10 keV . In this work, new segmented four-quadrant diodes for beam alignment purposes are fabricated on both ultrathin (10 μ m-thick) and bulk silicon substrates. Four-quadrant diodes implementing different design parameters as well as auxiliary test structures (single diodes and MOS capacitors) are studied. An extensive electrical characterization, including current-voltage (I-V) and capacitance-voltage (C-V) techniques, is carried out on non-irradiated and gamma-irradiated devices up to 100 Mrad doses. Special attention is devoted to the study of radiation-induced charge build-up in diode interquadrant isolation dielectric, as well as its impact on device interquadrant resistance. Finally, the devices have been characterized with an 8 keV laboratory X-ray source at 108 ph/s and in BL13-XALOC ALBA Synchroton beamline with 1011 ph/s and energies from 6 to 16 keV . Sensitivity, spatial resolution and uniformity of the devices have been evaluated.

Electrical properties of NiFe2O4 epitaxial ultra-thin films

Epitaxial thin films of NiFe2O4 are fabricated by pulsed laser deposition on SrTiO3 substrate. Symmetrical capacitor-like structures are formed using SrRuO3 as bottom and top electrodes. Electrical characterizations, including current–voltage, capacitance–voltage and capacitance–frequency measurement, reveal a hysteresis-like behaviour for current and capacitance as function of voltage. This could be assigned to a resistive and/or capacitive switching. A “degradation” process takes place after repeated voltage cycling or after heating the sample to 400 K, leading to the stabilization of different resistive states. These features can be related to the changes observed in the capacitance–frequency characteristics, suggesting the presence of a relaxation mechanism at low frequencies, and can be associated with the presence of a deep donor-type level in the band-gap of the NiFe2O4 layer.

High-κ NdTaO4 dielectrics deposited on polycrystalline silicon substrates

High-k NdTaO4 dielectrics annealed with various temperatures were first deposited on polycrystalline silicon substrates. Material and electrical characterizations were performed. To examine the crystalline structures, X-ray diffraction patterns were analyzed. Electrical measurements including current–voltage characteristics, constant current stress, and the Weibull plots show that annealing could enhance the breakdown voltages, lower the trapping rate, and strengthen the reliability. Results indicate that annealing at 900 °C may optimize the dielectric performance. This dielectric shows promise for future gate material or flash memory integrated with current NdTaO4-based optical devices.

Smart modification of the single conical nanochannel to fabricate dual-responsive ion gate by self-initiated photografting and photopolymerization

A simple, rapid and general method of self-initiated photografting and photopolymerization (SIPGP) was first introduced to fabricate dual-responsive nanochannel with a solid-state conical nanopore for the first time. The high density of carboxyl and hydroxyl groups on the internal surface of the etched poly(ethylene terephthalate) (PET) nanochannel acted as photo-active sites to provide further growth and amplification of polymer brushes via SIPGP. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) was chosen as a prototypical polymer which can be grafted on the surface of the nanochannel with high efficiency. SIPGP provided a smart and simple strategy to graft polymer brush on the surface of the nanochannel without the need of a surface bonded initiator. Series of characterizations including current–voltage curves, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) indicated the successful construction of the polymer. The functionalized nanochannel was finally used for the construction of smart gate with perfect responsibility, reversibility and stability towards CO2 and temperature. This modification strategy combined with unique character of the polymer may hold a great potential in building various smart responsive systems.

Analysis of the Microstructure Formation Process and Its Influence on the Performance of Polymer Electrolyte Fuel‐Cell Catalyst Layers

AbstractTo understand the formation process of the microstructure of the catalyst layer of a polymer electrolyte fuel cell (PEFC), we tried to observe the “real” structure of the catalyst ink by cryogenic scanning electron microscopy (cryo‐SEM). Catalyst inks with different water/alcohol compositions were successfully visualized, and they correlated well with the particle‐size distribution obtained by laser diffraction of the ink and the structures of the catalyst layers obtained by typical SEM. On the basis of other electrochemical characterization results, including current–voltage performance, oxygen reduction reaction kinetics, and mass‐transport properties, the microstructures of the catalyst inks and the catalyst layers were proposed. The proposed microstructures can explain the relationship between the catalyst materials and the performance of the cathode catalyst layer of the membrane electrode assembly through its formation and apparent properties. It was also found that the microstructure of the catalyst ink plays an important role in performance.

Information extraction from FN plots of tungsten microemitters

Tungsten based microemitter tips have been prepared both clean and coated with dielectric materials. For clean tungsten tips, apex radii have been varied ranging from 25 to 500 nm. These tips were manufactured by electrochemical etching a 0.1 mm diameter high purity (99.95%) tungsten wire at the meniscus of two molar NaOH solution. Composite micro-emitters considered here are consisting of a tungsten core coated with different dielectric materials-such as magnesium oxide (MgO), sodium hydroxide (NaOH), tetracyanoethylene (TCNE), and zinc oxide (ZnO). It is worthwhile noting here, that the rather unconventional NaOH coating has shown several interesting properties. Various properties of these emitters were measured including current-voltage (IV) characteristics and the physical shape of the tips. A conventional field emission microscope (FEM) with a tip (cathode)-screen (anode) separation standardized at 10 mm was used to electrically characterize the electron emitters. The system was evacuated down to a base pressure of ∼10(-8) mbar when baked at up to ∼180 °C overnight. This allowed measurements of typical field electron emission (FE) characteristics, namely the IV characteristics and the emission images on a conductive phosphorus screen (the anode). Mechanical characterization has been performed through a FEI scanning electron microscope (SEM). Within this work, the mentioned experimental results are connected to the theory for analyzing Fowler-Nordheim (FN) plots. We compared and evaluated the data extracted from clean tungsten tips of different radii and determined deviations between the results of different extraction methods applied. In particular, we derived the apex radii of several clean and coated tungsten tips by both SEM imaging and analyzing FN plots. The aim of this analysis is to support the ongoing discussion on recently developed improvements of the theory for analyzing FN plots related to metal field electron emitters, which in particular introduces a new form of intercept correction factors. The results derived demonstrate the applicability of the applied method on needle shaped - i.e. non planar - emitters as well as its limits.

Processing and Electrical Characterization of Metal-Oxide-Semiconductor Structures Prepared by DBSA-Doped TiO2 Nanoparticles

In the present study, using sol-gel method titanium dioxide (TiO2) nanoparticles with a new doping material have been synthesized, and a Dodecyl Benzene Sulfonic Acid (DBSA)-doped TiO2/p-Si Metal-Oxide-Semiconductor (MOS) structure has been fabricated. The characterizations of the structural and morphological properties of the DBSA-doped TiO2 nanoparticles have been carried out by means of X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM), respectively. The XRD results show that DBSA-doped TiO2 have a crystalline rutile phase along the (110) growth direction. It was confirmed from AFM images that the nanostructure of DBSAdoped TiO2 is grown as rock-like. The electrical characteristics of the device have also been performed, including current–voltage (I–V) and capacitance–voltage (C–V) at room temperature.

Improvement of Surge Protection by Using an AlGaN/GaN-Based Metal–Semiconductor–Metal Two-Dimensional Electron Gas Varactor

In this paper, a varactor with metal–semiconductor–metal diodes on top of the (NH4)2S/P2S5-treated AlGaN/GaN two-dimensional electron gas epitaxial structure (MSM-2DEG) is proposed to the surge protection for the first time. The sulfur-treated MSM-2DEG varactor properties, including current–voltage (I–V), capacitance–voltage (C–V), and frequency response of the proposed surge protection circuit, are presented. To verify its capability of surge protection, we replace the metal oxide varistor (MOV) and resistor (R) in a state-of-the-art surge protection circuit with the sulfur-treated MSM-2DEG varactor under the application conditions of system-level surge tests. The measured results show that the proposed surge protection circuit, consisted of a gas discharge arrester (GDA) and a sulfur-treated MSM-2DEG varactor, can suppress an electromagnetic pulse (EMP) voltage of 4000 to 360 V, a reduction of 91%, whereas suppression is to 1780 V, a reduction of 55%, when using only a GDA.

The Development of Hydrazine‐Processed Cu(In,Ga)(Se,S)2 Solar Cells

AbstractThe hydrazine‐based deposition of Cu(In,Ga)(S,Se)2 (CIGS) thin films has attracted considerable attention in recent years due to its potential for the high‐throughput production of photovoltaic devices based on this absorber material. This article provides an introduction as well as presenting a complete picture of the current status of hydrazine‐based CIGS solar‐cell fabrication, including the three major steps of this deposition process: dissolution of the precursor materials in hydrazine, deposition of a film from the resulting precursor solution, and the completion and characterization of a photovoltaic device following absorber deposition. Recent discoveries are then discussed, regarding the dissolution chemistry of the relevant precursor complexes in hydrazine, which together represent the true foundation of this processing method. Recent studies on CIGS film formation are then summarized, including the control and analysis of the crystalline phase, electronic bandgap, and film morphology. Finally, the latest progress in high‐performance device fabrication is highlighted, with a focus on optoelectronic characterization including current–voltage, junction capacitance, and minority carrier lifetime measurements. Finally, a discussion and future outlook is provided.

Photoelectron Properties of Nanocrystalline TiO2 Films Prepared by a Powerful Hydrothermal Technique

In this article, nanocrystalline anatase TiO2 films were prepared using a powerful hydrothermal technique and characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopic (XPS), and UV–vis absorption spectra. A metal–semiconductor–metal ultraviolet (UV) detector based on TiO2 films with Au electrodes was fabricated. The photoelectron properties of the TiO2 films, including current–voltage (I–V) curves under UV illumination, spectral response and response time were studied in detail. The results of the experiment demonstrate that the crystallinity of the TiO2 film was greatly improved by the hydrothermal technique: the atom ratio between Ti and O on the surface of TiO2 film is calculated to be 1.87:1, which indicates that the obtained TiO2 film has less oxygen vacancies. The improved crystallinity as well as the correspondingly decreased hole trap concentrations finally resulted in a short photoresponse decay time of 4.183 s. Meanwhile, a responsivity of 56.5 mA/W, a low dark current of 5.95 nA, a UV photo-to-dark current ratio of 103 were also obtained for the TiO2-based detector, all of which suggest that the fabricated TiO2 films are very promising in UV detection applications.