Search Results (1,108)

As MicroLED technology scales below 10 μm, Cu is increasingly utilized for interconnects due to its high thermal and electrical conductivity. However, Cu-induced degradation in GaN remains a critical reliability concern. This study investigates 10 nm Ni, Ti, and Pt barriers in Cu/Al stacks on green GaN-on-Si devices with a mesa diameter of 350 μm after isothermal annealing at 100 °C, 200 °C, and 300 °C for 2 h, aiming to provide a reference for future barrier design in scaled MicroLED devices. Electrical and electroluminescence measurements show that while 100–200 °C annealing optimizes contact resistance, higher temperatures cause Cu interdiffusion with metal-dependent severity. Ti emerges as the optimal general-purpose barrier, achieving the highest EL intensity among annealed samples at 300 °C, demonstrating that higher-temperature annealing enhances rather than degrades performance, thanks to effective Cu blocking and improved contact formation. Pt offers comparable barrier effectiveness with superior thermal stability, maintaining stable electrical characteristics and retaining 42% of peak EL intensity even at 300 °C. In contrast, Ni exhibits insufficient blocking, suffering 83% EL quenching and severe electrical degradation at 300 °C. Notably, as-deposited PtCuAl devices show an unexpected carrier localization effect yielding the highest recorded EL intensity (2750 a.u.), suggesting contact engineering opportunities. These findings establish a barrier effectiveness hierarchy (Ti ≈ Pt >> Ni) for thermal stability. Full article

The κ-phase gallium oxide (κ-Ga₂O₃) has emerged as a promising material for next-generation electronic devices owing to its ultra-wide band gap, remarkable spontaneous polarization and unique ferroelectricity. We have investigated the two-dimensional electron gas (2DEG) characteristics and device performance of κ-Ga₂O₃/GaN HEMTs via numerical simulations. The κ-Ga₂O₃/GaN heterostructure exhibits a significantly enhanced 2DEG density (~1.05 × 10¹⁴ cm⁻²), which is nearly an order of magnitude higher than that of conventional AlGaN/GaN HEMTs, due to the strong polarization effect. For a barrier thickness of 25 nm, the κ-Ga₂O₃/GaN HEMT exhibits a maximum drain current density (I_D,max) of 4.40 A/mm at V_GS = 2 V and a peak transconductance (g_m,max) of 0.45 S/mm, accompanied by a steep subthreshold swing (SS) of 63.2 mV/decade. Furthermore, we find that the absolute value of threshold voltage increases with the barrier thickness and the peak transconductance decreases with the increase in barrier thickness. When the thickness reaches 40 nm, the 2DEG density becomes saturated with a value of 1.12 × 10¹⁴ cm⁻². Moreover, by incorporating a p-type GaN cap layer into the κ-Ga₂O₃/GaN heterostructure, a normally off operation is achieved, with a positive threshold voltage as the acceptor concentration exceeds 8.0 × 10¹⁷ cm⁻³. These results highlight the potential of κ-Ga₂O₃/GaN heterostructures for high-performance power electronic applications. Full article

This study investigates the electronic and nonlinear optical properties of coupled GaN/AlN quantum dots using a numerical approach based on coordinate transformation combined with the finite difference method (FDM). The Schrödinger equation is solved to determine the electronic energy levels and wave functions of the system, which are subsequently used to evaluate the nonlinear optical rectification (NOR) response. Since numerical simulations become computationally expensive for large quantum dot systems, several regression-based models, including Polynomial Regression, Ridge Regression, LASSO, and Elastic Net, are trained on high-fidelity numerical data. These models learn the relationship between structural parameters and the resulting electronic and optical properties, enabling fast and reliable predictions for larger quantum dot configurations. The predictive performance of the ML models is assessed by comparing their results with the numerical simulations, showing excellent agreement while significantly reducing computational effort. The proposed hybrid physics–machine learning framework therefore provides an efficient and reliable approach for predicting the electronic and nonlinear optical behavior of coupled GaN/AlN quantum dots. Full article

The work is a continuation of studies , focused on the development of fundamental principles of aluminum activation by low-melting metals forming eutectic alloys with fine-grained structure and limited solid solubility. The aim of this work is to investigate the mechanism and kinetics of the interaction of aluminum-based eutectic alloys with water and aqueous electrolytes. Analysis of phase diagrams of binary systems (Al–Ga, Al–In, In–Ga, Al–Sn, Sn–Ga, Al–Zn, Zn–Ga) shows that alloy composition governs surface heterogeneity and reactivity. Ternary and quaternary systems (Al–In–Ga, Al–Sn–Ga, Al–In–Sn–Ga) exhibit enhanced interaction with water due to increased heterogeneity, leading to the formation of numerous microgalvanic couples and accelerated aluminum dissolution. The process is characterized by the stationary potential of aluminum and involves coupled chemical, electrochemical, and topochemical stages described by the Avrami–Erofeev equation, with n ≈ 1.27–2.07. An increase in the In–Ga or In–Sn–Ga fraction reduces the activation energy: 9.1 kcal/mol (82% Al–9% Ga–9% Sn), 11.4 kcal/mol (92% Al–4% Ga–4% In), and 15.5 kcal/mol (91% Al–3% Ga–3% In–3% Sn). Full article

Gate definition is a major challenge in p-GaN gate AlGaN/GaN HEMT structures because of the high selectivity and low plasma damage required during the etching process. In this work, self-terminated etching, developed to limit surface damage and loss of the underlying AlGaN layer, is investigated. A comparison of two over-etch chemistries (Cl₂/O₂/N₂ and BCl₃/SF₆) revealed that the oxygen-based process yields superior results in terms of AlGaN surface morphology, producing a smoother surface and a more conformal p-GaN profile, while the fluorine-based process exhibited more anisotropic behavior, leading to p-GaN residues and surface pitting. To address across-wafer non-uniformity, a temperature gradient strategy using the tunable electrostatic chuck was developed. The optimized process was evaluated through automatic defect control and device robustness under drain bias-stress. A total reduction in defectivity and reliable HEMT devices across the wafer under high drain-source bias were achieved. These results demonstrate the effectiveness of the proposed solution, offering significant improvements in process efficiency and manufacturability. Full article

An experimental and numerical study of the on-resistance degradation in AlGaN/GaN-based technology is presented. Back-bias measurements on transmission-line-method (TLM) structures were performed to investigate the mechanism underlying the current degradation. The observed TLM current collapse exhibits Arrhenius behavior, which is associated with traps in the buffer layers. Interestingly, the decay time of the collapse shows a decreasing trend with increasing applied bias, which is here investigated and newly interpreted as a signature of Poole–Frenkel bias-enhanced trap emission. An effective model is discussed and implemented in TCAD simulations to support the experimental findings. In addition to providing justification for the temperature and applied-voltage dependence of the observed degradation trends, the proposed mechanism can also explain the spread in the activation energies measured for acceptor traps in the buffer layers, as reported in the literature for AlGaN/GaN technologies. Full article

Bandstructure methods occupy a central place in the physics of nanostructures, and the multiband $\mathit{k}·\mathit{p}$ theory of Luttinger, Kohn, and Kane has served as one of the most widely used computational frameworks for modelling electronic states and energies in low-dimensional semiconductor systems for several decades. Despite its broad success, the theory harbours a fundamental mathematical difficulty that has been largely overlooked: the multiband Luttinger–Kohn Hamiltonians are non-elliptic partial differential operators for the overwhelming majority of common III–V and III-nitride crystalline materials, a fact that violates the axiomatic requirements of quantum mechanics and is the root cause of the long-standing problem of spurious solutions. In this paper, we derive ellipticity conditions rigorously for the $6\times 6$, $8\times 8$, and $14\times 14$ zinc-blende Hamiltonians, demonstrating that non-ellipticity affects a substantially larger class of materials than previously reported. We develop and justify a systematic parameter rescaling procedure for the $8\times 8$ Kane Hamiltonian and obtain admissible parameter sets for GaAs, AlAs, InAs, GaP, AlP, InP, GaSb, AlSb, InSb, GaN, AlN, and InN. The inversion-asymmetry parameter B is shown to play an essential and previously unrecognized role in maintaining ellipticity, and it is used to optimize the bandstructure fit of the rescaled parameter sets. Analysis of several known $14\times 14$ models reveals structural sources of non-ellipticity, pointing to the need for a revision of perturbative assumptions regarding out-of-basis band contributions. The consistent parametrization framework developed here provides the rigorous mathematical foundation required by inverse design methodologies, AI-enhanced electronic structure calculations, and data-driven multifidelity approaches in nanoscience and nanotechnology. Full article

In this work, we develop machine-learned moment tensor potentials (MTPs) to simulate the static and dynamic structural properties in Al_xGa_1−xN and related materials. The potentials are trained on DFT-calculated data for forces, stresses, and energies obtained from random atomic displacements and cell deformations. MTP-calculated physical properties, including lattice parameters and elastic constants, thermal expansion, harmonic and anharmonic vibrational properties, and the thermal conductivity, are benchmarked against first-principles results and experimental data. The comparisons testify to the very high accuracy achieved by the machine-learned potentials despite the massively reduced computational effort. Additionally, the impact of various aspects of the MTP training procedure is examined. Full article

In the renewable energy-driven “green electricity–green hydrogen–green ammonia” pathway, the development of low-temperature and low-energy-consumption ammonia synthesis technologies is of great significance. In this work, a plasma-catalytic ammonia synthesis system was established using a coaxial dielectric barrier discharge (DBD) reactor. The effects of different catalysts, including Ag, Cu, γ-Al₂O₃, BaTiO₃ and Co/BaTiO₃, Ni/BaTiO₃ on ammonia synthesis performance were systematically investigated. The reaction process was analyzed using voltage–current waveforms, Lissajous figures, and optical emission spectroscopy (OES). The results show that different catalytic systems have a significant influence on ammonia synthesis performance, with the promotional effect ranked as follows: Ni/BaTiO₃ > Co/BaTiO₃ > BaTiO₃ > Ag > γ-Al₂O₃ > Cu. Among them, Ni/BaTiO₃ exhibited the best performance. Under the conditions of N₂:H₂ = 1:1 and a gas flow rate of 2.5 L/min, the NH₃ synthesis rate reached 259.48 μmol/min, and the maximum energy efficiency reached 1.40 g-NH₃/kWh. Catalyst characterization results indicate that the BaTiO₃ support maintained a stable crystal structure, while the loaded metal species were highly dispersed and uniformly distributed on the support surface, which is beneficial for the adsorption and conversion of reactive species on the catalyst surface. Discharge characteristic analysis shows that the introduction of BaTiO₃ enhanced the local electric field and improved the uniformity of micro-discharges, while the further incorporation of metal active components strengthened the micro-discharge behavior. OES results reveal that the intensities of characteristic emission lines, such as NH, N₂⁺, and Hα, were significantly enhanced in the Ni/BaTiO₃ system, facilitating the formation and conversion of NH_x intermediates. The superior performance of Ni/BaTiO₃ is attributed to the coupling between BaTiO₃-induced dielectric enhancement and Ni-promoted surface hydrogenation and NH₃ desorption. This work provides mechanistic insight into catalyst-dependent DBD plasma-catalytic ammonia synthesis and offers an experimental basis for the further optimization of plasma-based ammonia production. Full article

This study systematically investigates the intrinsic vertical breakdown characteristics of 8-inch GaN-on-Si high-electron-mobility transistor (HEMT) buffer layers (extending up to the GaN channel layer) using a vertical electrode configuration. By comparing samples with different carbon doping doses, AlN insertion layers, and superlattice cycle numbers (buffer layer thickness), combined with Technology Computer-Aided Design (TCAD) simulations, the relevant mechanisms are revealed. The results show that buffer layer thickness is a critical factor determining the vertical breakdown voltage. Its increase effectively reduces the longitudinal average electric field, widens the depletion region, and increases the breakdown voltage by approximately 50%. Carbon doping compensates for carriers and suppresses leakage through deep-level acceptor traps. Inserting thin AlN layers into the superlattice has a limited effect on improving breakdown voltage. This research provides clear experimental guidance for the optimal design of high-voltage GaN HEMT buffer layers from both material and physical perspectives. Full article

Titanium alloy welded joints are key parts of deep-sea pressure hulls, which are subjected to fatigue loadings in service. In this study, axial fatigue tests, mode I fatigue crack growth tests, and mixed-mode I–II fatigue crack growth tests were conducted on the Ti-6Al-4V ELI titanium alloy welded joint, and its fatigue failure mechanism and crack growth behavior is investigated and compared with the base material. The results show that the S–N curve of Ti-6Al-4V ELI titanium alloy welded joints has a very similar slope as the base material, but its fatigue performance is lower than the base material. However, the welded joints exhibit a higher resistance in the near-threshold region under mode I loading compared to the base material. Scanning electron microscope observation indicates that the fatigue crack mainly initiates from gas pores during welding for the Ti-6Al-4V ELI titanium alloy welded joints. Under mixed-mode I–II loading, the stress intensity factor range component $\mathsf{\Delta }{K}_{\mathrm{I}}$ of welded joints is higher than that of the base material, and an equivalent stress intensity factor range model is proposed to describe the crack growth rate under both mode I and mixed-mode I–II loadings. The new model incorporates a parameter dependent on the mode mixity ratio defined by $\mathsf{\Delta }{K}_{\mathrm{I}\mathrm{I}}/\mathsf{\Delta }{K}_{\mathrm{I}}$ in this paper, and it unifies the crack growth data well under mode I and mixed-mode I–II loadings. The paper indicates that the gas pores during welding are an important factor for the poor fatigue performance of Ti-6Al-4V ELI titanium alloy welded joints. Full article

As a representative wide-bandgap semiconductor material, gallium nitride (GaN) has attracted increasing attention because of its superior material properties (e.g., high electron mobility, high electron saturation velocity, and critical electric field). For power electronics applications, and to take full advantage of the superiorities of the GaN material, the normally off operation is required based on an AlGaN/GaN heterostructure. For a commercial approach, GaN HEMTs with a p-GaN gate have become a research hotspot. The characteristics of p-GaN gate HEMTs have a significant relationship with gate structure, especially the contact type on the p-GaN layer. In this review, the necessity of normally off operation and the advantages of adopting a p-GaN gate are elaborated, followed by the theory of achieving normally off operation by p-GaN and critical fabrication processes. The various gate structures are discussed, including metal gate, junction gate and hybrid gate structures on the p-GaN layer, to improve threshold voltage. Meanwhile, the methods required to optimize breakdown voltage and monolithically integrated technologies are also demonstrated. This review outlines the development and future trends of p-GaN gate HEMTs for power systems. Full article

HCM is the most prevalent cardiac disease in cats and is associated with substantial morbidity and mortality. Among its complications, FATE represents a major adverse clinical outcome. Conventional echocardiographic indices typically assess atrial or ventricular parameters separately and may not fully capture the structural relationship between the LA and LV. The left atrioventricular coupling index (LACI) is a volumetric ratio that combines LA remodeling and LV chamber size at end-diastole into a single structural index. This retrospective, cross-sectional observational study included 91 cats, classified according to ACVIM guidelines into healthy controls (n = 33), asymptomatic HCM (stage B1, n = 14; stage B2, n = 16), symptomatic HCM (stage C, n = 15), and cats with FATE (n = 13). Conventional and two-dimensional speckle-tracking echocardiography were performed, and LACI-ED was calculated as the ratio of LA end-diastolic volume to LV end-diastolic volume. LACI-ED increased progressively with disease severity (p < 0.001), showing the highest values in symptomatic HCM and FATE cases. It correlated positively with LA size and volume (p < 0.01) and inversely with LV GLS (p < 0.01). Exploratory ROC analysis for FATE status yielded limited discriminatory performance for LACI-ED > 150% (AUC = 0.575; 95% CI: 0.402–0.736; sensitivity 46.2%; specificity 84.4%). Although LACI-ED > 150% was associated with higher odds of prevalent FATE (OR = 4.65; 95% CI: 1.405–29.215; p = 0.020), this finding should be interpreted with caution. Pairwise comparisons of ROC curve areas between LACI-ED and conventional echocardiographic parameters (LA/Ao ratio, LA diameter, and LV GLS) revealed no statistically significant differences (all p > 0.05). Although LACI-ED > 150% was associated with higher odds of prevalent FATE (OR = 6.8; p < 0.05), this finding should be interpreted with caution. This cross-sectional study evaluates associations with disease stage and thromboembolic status at the time of examination. The findings suggest that LACI-ED reflects disease severity in feline HCM, whereas its utility for thromboembolic risk assessment appears limited. Full article

This study presents the production of isoamyl, n-butyl and cyclohexyl esters of levulinic acid with an excellent yield under solvent-free conditions. The catalysts used were MgAlO and M²⁺MgAlO-mixed oxides containing the transition metals (M²⁺ = Co²⁺, Ni²⁺, Zn²⁺), obtained from calcined layered double hydroxides (LDH). They are easily accessible, low-cost, and environmentally friendly and possess the requisite acid–base properties for esterification reactions. The effect of reaction time and the molar ratio of levulinic acid to the alcohols used on the esterification reaction was investigated. The catalysts were characterized by X-ray diffraction (XRD), XRF, SEM and temperature-programmed desorption of CO₂ (TPD-CO₂). Gas chromatography–mass spectroscopy (GC/MS) was used for the identification and quantification of the product mixtures. Mixed oxides containing transition metals exhibited significantly higher activity than MgAlO. Under the selected reaction conditions, the conversion of levulinic acid and the yield of isoamyl ester reached 100% at a reagent ratio of 1:1. As a by-product of esterification, only dicyclohexyl ether was found at a reactant ratio of 1:1.5. Full article

AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) have been widely deployed in water treatment, sterilization, and optical communication owing to their intrinsic merits of mercury-free operation, compact footprint, and fast turn-on capability. However, poor reliability and short operating lifetime, mainly caused by electrical degradation and poor heat dissipation, have severely limited their commercial applications. In this work, the degradation mechanism of 270 nm DUV LEDs was systematically studied via multi-condition accelerated aging tests. Results confirm that electrical stress is the dominant factor inducing device degradation, while thermal stress plays a secondary role. Electrical stress generates internal defects, increases leakage current and thermal resistance, enhances non-radiative recombination, and causes a sharp drop in light output power. Based on test data, the L70 lifetimes predicted by the inverse power law and the Arrhenius models are 5832 h and 5724 h, with relative errors of 8.59% and 10.28% compared with the measured 6380 h. This work provides reliable experimental support for the performance evaluation and lifetime prediction of DUV LEDs. Full article