Search Results (74)

Memristors with resistive switching capabilities are vital for information storage and brain-inspired computing, making them a key focus in current research. This study demonstrates non-volatile analog resistive switching behavior in Al/TiO_x/TiN/Si(n⁺⁺)/Al memristive devices. Analog resistive switching offers gradual, controllable conductance changes, which are essential for mimicking brain-like synaptic behavior, unlike digital/abrupt switching. The amorphous titanium oxide (TiO_x) active layer was deposited using the pulsed-DC reactive magnetron sputtering technique. The impact of increasing the oxide thickness on the electrical performance of the memristors was investigated. Electrical characterizations revealed stable, forming-free analog resistive switching, achieving endurance beyond 300 DC cycles. The charge conduction mechanisms underlying the current–voltage (I–V) characteristics are analyzed in detail, revealing the presence of ohmic behavior, Schottky emission, and space-charge-limited conduction (SCLC). Experimental results indicate that increasing the TiO_x film thickness from 31 to 44 nm leads to a notable change in the current conduction mechanism. The results confirm that the memristors have good stability (>1500 s) and are capable of exhibiting excellent long-term potentiation (LTP) and long-term depression (LTD) properties. The analog switching driven by oxygen vacancy-induced barrier modulation in the TiO_x/TiN interface is explained in detail, supported by a proposed model. The remarkable switching characteristics exhibited by the TiO_x-based memristive devices make them highly suitable for artificial synapse applications in neuromorphic computing systems. Full article

The enduring problem of CO₂ emissions and their consequent influence on the earth’s atmosphere has captured the attention of researchers. Photocatalytic CO₂ reduction holds great significance; however, it is constrained by the effect of carrier recombination. Simultaneously, the structural modification of heterojunction catalysts has emerged as a promising approach to boost the photocatalytic performance. Herein, Zn₂GeO₄@CeO₂ core@shell nanorods were prepared by a simple self-assembly method for photocatalytic CO₂ reduction. The thickness of the CeO₂ shell can be regulated rapidly and conveniently. The photocatalytic results indicate that the structure regulation could affect the photocatalytic performance by controlling the amount of active sites and the shielding effect. X-ray photoelectron spectroscopy (XPS) and Mott–Schottky analyses reveal that Zn₂GeO₄ and CeO₂ formed Type-I heterojunctions, which prolonged the lifetime of the photogenerated carriers. The CO₂ adsorption and activation capacities of CeO₂ also exert a beneficial influence on the progress of CO₂ photoreduction, thus enabling efficient photocatalytic CO₂ reduction. Moreover, the in situ FT-IR spectra show that Zn₂GeO₄@CeO₂ suppresses the formation of byproduct intermediates and shows higher CO selectivity. The best sample of Zn₂GeO₄@0.07CeO₂ can exhibit a CO yield of as high as 1190.9 μmol g⁻¹ h⁻¹. Full article

The transition of SiC MOSFET structure from planar to trench-based architectures requires the optimization of gate dielectric layers to improve device performance. This study utilizes a range of characterization techniques to explore the interfacial properties of ZrO₂ and SiO₂/ZrO₂ gate dielectric films, grown via atomic layer deposition (ALD) in SiC epitaxial trench structures to assess their performance and suitability for device applications. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements showed the deposition of smooth film morphologies with roughness below 1 nm for both ZrO₂ and SiO₂/ZrO₂ gate dielectrics, while SE measurements revealed comparable physical thicknesses of 40.73 nm for ZrO₂ and 41.55 nm for SiO₂/ZrO₂. X-ray photoelectron spectroscopy (XPS) shows that in SiO₂/ZrO₂ thin films, the binding energies of Zr 3d_5/2 and Zr 3d_3/2 peaks shift upward compared to pure ZrO₂. Electrical characterization showed an enhancement of E_BR (3.76 to 5.78 MV·cm⁻¹) and a decrease of I_{ON_EBR} (1.94 to 2.09 × 10⁻³ A·cm⁻²) for the SiO₂/ZrO₂ stacks. Conduction mechanism analysis identified suppressed Schottky emission in the stacked film. This indicates that the incorporation of a thin SiO₂ layer effectively mitigates the small bandgap offset, enhances the breakdown electric field, reduces leakage current, and improves device performance. Full article

In this paper, we investigated the effects of the processing parameters, such as deposition methods, annealing temperature, and metal thickness, on the electrical characteristics of Ti/4H-SiC contacts. A reduction of the Schottky barrier height from 1.19 to 1.00 eV following an increase of the annealing temperature (475–700 °C) was observed for a reference contact with an 80 nm-thick Ti layer. The current transport mechanisms can be described according to the thermionic emission (TE) and thermionic field emission (TFE) models under forward and reverse biases, respectively. The comparison with an e-beam evaporated Ti(80 nm)/4H-SiC contact did not show significant differences for the forward characteristics, while an increase of the leakage current was observed under high reverse voltage (>500 V). Finally, a thickness variation from 10 to 80 nm induced a reduction of the Schottky barrier height, due to the reaction occurring at the interface with a Ti-Al region extended up to the 4H-SiC surface. In addition to a deeper understanding of the Schottky barrier properties, this work is useful for the development of Schottky barrier diodes with tailored characteristics. Full article

In this work, the electrical properties of the Ga₂O₃ Schottky barrier diodes (SBDs) using W/Au as the Schottky metal were investigated. Due to the 450 °C post-anode annealing (PAA), the reduced oxygen vacancy defects on the β-Ga₂O₃ surface resulted in the improvement in the forward characteristics of the W/Au Ga₂O₃ Schottky diode, and the breakdown voltage was significantly enhanced, increasing by 56.25% from 400 V to 625 V after PAA treatment. Additionally, the temperature dependence of barrier heights and ideality factors was analyzed using the thermionic emission (TE) model combined with a Gaussian distribution of barrier heights. Post-annealing reduced the apparent barrier height standard deviation from 112 meV to 92 meV, indicating a decrease in barrier height fluctuations. And the modified Richardson constants calculated for the as-deposited and annealed samples were in close agreement with the theoretical value, demonstrating that the barrier inhomogeneity of the W/Au Ga₂O₃ SBDs can be accurately explained using the TE model with a Gaussian distribution of barrier heights. Full article

Interface-passivated graphene/silicon Schottky junction solar cells have demonstrated promising features with improved stability and power conversion efficiency (PCE). However, there are some misunderstandings in the literature regarding some of the working mechanisms and the impacts of the silicon/insulator interface. Specifically, attributing performance improvement to oxygen vacancies and characterizing performance using Schottky barrier height and ideality factor might not be the most accurate or appropriate. This work uses Al₂O₃ as an example to provide a detailed discussion on the interface ALD growth of Al₂O₃ on silicon and its impact on graphene electrode metal–insulator–semiconductor (MIS) solar cells. We further suggest that the current conduction in MIS solar cells with an insulating layer of 2 to 3 nm thickness is better described by direct tunneling, Poole–Frenkel emission, and Fowler–Nordheim tunneling, as the junction voltage sweeps from negative to a larger forward bias. The dielectric film thickness, its band offset with Si, and the interface roughness, are key factors to consider for process optimization. Full article

In this study, we propose a simple measurement technique to quantitatively measure the time taken by threshold voltage of normally-off p-GaN AlGaN/GaN HEMTs to recover from a nominal operational gate stress-induced instability. The proposed technique eliminates the requirement to perform a full transfer characteristic sweep post-stress, thereby eliminating the measurement-induced instability effect, often colluding precise recovery time measurement. The rate of recovery and extracted recovery times hold significance in empirically correlating the location of traps in the p-GaN or AlGaN barrier region causing V_TH instability. The gate of the HEMT is stressed at nominal operational drive voltages 1.5 V, 2 V, and 4 V for various time intervals from 500 μs to 100 s, and the time taken for the drain current to recover to prestress levels measured at near-threshold voltage (~1.1 V_TH) is measured as the threshold voltage recovery time. With increasing gate stress voltages, 2DEG gets trapped at relatively deeper trap energy levels at the AlGaN/GaN interface requiring more emission time during the process of recovery, mandating larger recovery times. At higher stress voltage of 4 V, the Schottky gate leakage current is high enough enabling injected holes to cross the AlGaN barrier and counter-compensate for the deeply trapped 2DEG, requiring relatively the same recovery times as lower stress voltages where the gate leakage is negligibly small. With increasing stress time, the amount of 2DEG trapped increases, requiring more recovery time to de-trap and beyond a certain time, saturation of the trap density occurs causing the recovery time to plateau. Full article

Oil-pressboard/paper insulation materials are essential in transformers for ensuring their safe and stable operation, primarily due to their roles in spatial electric field distribution and charge migration mechanisms. Current spatial distribution analyses rely on computational methods that lack empirical validation, particularly for oil-pressboard/paper composites. This study leverages the principles of the Kerr electro-optic effect to develop a rapid measurement platform for electric fields within oil-pressboard/paper insulation under impulse voltage conditions, which measures the spatial electric field characteristics using Cu-Cu and Al-Al electrodes under various scenarios: with asymmetric and symmetric pressboard coverage and different numbers of insulating paper layers. Findings indicated: (1) In asymmetric pressboard models, Cu-Cu electrodes exhibit a consistent peak electric field of approximately 16 kV/mm, while Al-Al electrodes show peak values of 18.13 kV/mm and −14.98 kV/mm. Charge density patterns are similar, with Cu-Cu at about 68 μC/m² and Al-Al at 11.2 μC/m² and −124.8 μC/m². (2) Symmetric models present consistent peak electric fields and charge densities for both polarities. (3) Increasing insulating paper layers elevates electric field strengths. Both electrodes show the similar peak field of about 17 kV/mm with differing paper layers due to higher charge injection from the Al electrode. (4) Utilizing the Schottky effect and field emission principles, the study clarifies charge generation and migration mechanisms. These insights could provide a theoretical foundation for designing and verifying oil-pressboard/paper insulation structures in transformers. Full article

Converting carbon dioxide (CO₂) into high-value-added chemicals using solar energy is a promising approach to reducing carbon dioxide emissions; however, single photocatalysts suffer from quick the recombination of photogenerated electron–hole pairs and poor photoredox ability. Herein, silver (Ag) nanoparticles featuring with localized surface plasmon resonance (LSPR) are combined with g-C₃N₄ to form a Schottky junction for photothermal catalytic CO₂ reduction. The Ag/g-C₃N₄ exhibits higher photocatalytic CO₂ reduction activity under UV-vis light; the CH₄ and CO evolution rates are 10.44 and 88.79 µmol·h⁻¹·g⁻¹, respectively. Enhanced photocatalytic CO₂ reduction performances are attributed to efficient hot electron transfer in the Ag/g-C₃N₄ Schottky junction. LSPR-induced hot electrons from Ag nanoparticles improve the local reaction temperature and promote the separation and transfer of photogenerated electron–hole pairs. The charge carrier transfer route was investigated by in situ irradiated X-ray photoelectron spectroscopy (XPS). The three-dimensional finite-difference time-domain (3D-FDTD) method verified the strong electromagnetic field at the interface between Ag and g-C₃N₄. The photothermal catalytic CO₂ reduction pathway of Ag/g-C₃N₄ was investigated using in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS). This study examines hot electron transfer in the Ag/g-C₃N₄ Schottky junction and provides a feasible way to design a plasmonic metal/polymer semiconductor Schottky junction for photothermal catalytic CO₂ reduction. Full article

For operation as power amplifiers in RF applications, high electron mobility transistor (HEMT) structures are subjected to a range of bias conditions, applied at both the gate and drain terminals, as the device is biased from the OFF- to ON-state conditions. The stability of the device threshold voltage (V_t) condition is imperative from a circuit-design perspective and is the focus of this study, where stresses in both the ON and OFF states are explored. We see rapid positive threshold voltage increases under negative bias stress and subsequent recovery (i.e., V_t reduces), whereas conversely, we see a negative V_t shift under positive stress and V_t increase during the subsequent relaxation phase. These effects are correlated with the thickness of the GaN layer and ultimately result from the deep carbon-acceptor levels in the C-GaN back barrier incorporated to screen the buffer between the silicon substrate and the epitaxially grown GaN layer. Methods to mitigate this effect are explored, and the consequences are discussed. Full article

In this study, the resistive switching phenomena in TiN/Ti/HfO₂/Ti metal–insulator–metal stacks is investigated, mainly focusing on the analysis of set and reset transitions. The electrical measurements in a wide temperature range reveal that the switching transitions require less voltage (and thus, less energy) as temperature rises, with the reset process being much more temperature sensitive. The main conduction mechanism in both resistance states is Space-charge-limited Conduction, but the high conductivity state also shows Schottky emission, explaining its temperature dependence. Moreover, the temporal evolution of these transitions reveals clear differences between them, as their current transient response is completely different. While the set is sudden, the reset process development is clearly non-linear, closely resembling a sigmoid function. This asymmetry between switching processes is of extreme importance in the manipulation and control of the multi-level characteristics and has clear implications in the possible applications of resistive switching devices in neuromorphic computing. Full article

In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm², a specific on-resistance ${\mathrm{R}}_{\mathrm{O}\mathrm{N},\mathrm{s}\mathrm{p}}$ of 1.9 mΩ cm² despite the current crowding effect in quasi-vertical structures, and an on/off current ratio (I_on/I_off) of 10¹⁰. Temperature-dependent current–voltage characteristics were measured in the range of 313–433 K to investigate the mechanisms of leakage conduction in the device. At near-zero bias, thermionic emission (TE) was found to dominate. By increasing up to 10 V, electrons gained enough energy to excite into trap states, leading to the dominance of Frenkel–Poole emission (FPE). For a higher voltage range (−10 V to −40 V), the increased electric field facilitated the hopping of electrons along the continuum threading dislocations in the “bulk” GaN layers, and thus, variable range hopping became the main mechanism for the whole temperature range. This work provides an in-depth insight into the leakage conduction transport on pseudo-vertical GaN-on-Si Schottky barrier diodes (SBDs) grown by localized epitaxy. Full article

We conducted a comparative study on the characterization of Ga-polar and N-polar GaN metal–insulator–semiconductor (MIS) Schottky contact with a SiN_x gate dielectric. The correlation between the surface morphology and the current–voltage (I–V) characteristics of the Ga- and N-polar GaN Schottky contact with and without SiN_x was established. The insertion of SiN_x helps in reducing the reverse leakage current for both structures, even though the leakage is still higher for N-polar GaN, consistent with the Schottky barrier height calculated using X-ray photoelectron spectroscopy. To optimize the electric property of the N-polar device, various substrate misorientation angles were adopted. Among the different misorientation angles of the sapphire substrate, the GaN MIS Schottky barrier diode grown on 1° sapphire shows the lowest reverse leakage current, the smoothest surface morphology, and the best crystalline quality compared to N-polar GaN grown on 0.2° and 2° sapphire substrates. Furthermore, the mechanism of the reverse leakage current of the MIS-type N-polar GaN Schottky contact was investigated by temperature-dependent I–V characterization. FP emissions are thought to be the dominant reverse conduction mechanism for the N-polar GaN MIS diode. This work provides a promising approach towards the optimization of N-polar electronic devices with low levels of leakage and a favorable ideality factor. Full article

In pursuit of realizing neuromorphic computing devices, we demonstrated the high-performance synaptic functions on the top-to-bottom Au/ZnVO/Pt two-terminal ferroelectric Schottky junction (FSJ) device architecture. The active layer of ZnVO exhibited the ferroelectric characteristics because of the broken lattice-translational symmetry, arising from the incorporation of smaller V⁵⁺ ions into smaller Zn²⁺ host lattice sites. The fabricated FSJ devices displayed an asymmetric hysteresis behavior attributed to the ferroelectric polarization-dependent Schottky field-emission rate difference in between positive and negative bias voltage regions. Additionally, it was observed that the magnitude of the on-state current could be systematically controlled by changing either the amplitude or the width of the applied voltage pulses. Owing to these voltage pulse-tunable multi-state memory characteristics, the device revealed diverse synaptic functions such as short-term memory, dynamic range-tunable long-term memory, and versatile rules in spike time-dependent synaptic plasticity. For the pattern-recognition simulation, furthermore, more than 95% accuracy was recorded when using the optimized experimental device parameters. These findings suggest the ZnVO-based FSJ device holds significant promise for application in next-generation brain-inspired neuromorphic computing systems. Full article

This research examines the influence of adding a commercial ionic liquid to the electrolyte during the electrochemical anodization of tungsten for the fabrication of WO₃ nanostructures for photoelectrochemical applications. An aqueous electrolyte composed of 1.5 M methanesulfonic acid and 5% v/v [BMIM][BF₄] or [EMIM][BF₄] was used. A nanostructure synthesized in an ionic-liquid-free electrolyte was taken as a reference. Morphological and structural studies of the nanostructures were performed via field emission scanning electron microscopy and X-ray diffraction analyses. Electrochemical characterization was carried out using electrochemical impedance spectroscopy and a Mott–Schottky analysis. From the results, it is highlighted that, by adding either of the two ionic liquids to the electrolyte, well-defined WO₃ nanoplates with improved morphological, structural, and electrochemical properties are obtained compared to samples synthesized without ionic liquid. In order to evaluate their photoelectrocatalytic performance, the samples were used as photocatalysts to generate hydrogen by splitting water molecules and in the photoelectrochemical degradation of methyl red dye. In both applications, the nanostructures synthesized with the addition of either of the ionic liquids showed a better performance. These findings confirm the suitability of ionic liquids, such as [BMIM][BF₄] and [EMIM][BF₄], for the synthesis of highly efficient photoelectrocatalysts via electrochemical anodization. Full article