Current Applied Physics最新文献

The optoelectronic performance of AlGaN-based deep ultraviolet micro-light emitting diodes are strongly affected by surface recombination at the mesa sidewall. Herein, the influence of sidewall defect density and location changes on the photoelectric properties and carrier recombination mechanisms were theoretically investigated. The results indicate a significant deterioration in the internal quantum efficiency and optical power with an increase in the sidewall defect density at the edge of the LED mesa. This deterioration is attributed to the Shockley-Read-Hall nonradiative recombination caused by sidewall defects. The sidewall defects also act as traps for electrons and holes, significantly affecting the carrier injection capability. Furthermore, the position dependence of carrier concentration and recombination rate along the lateral dimension of the LED mesa were studied. The results show that etching process not only causes sidewall damage but can damage the quality of internal epitaxial materials. These effects should be minimized by optimizing the dry-etching process.

Neuromorphic computing is a next‐generation computing technology featured by parallel data processing and adaptive learning. Two significant factors that improve learning accuracy are the ‘dynamic range’ and ‘linearity’ of the weight update. In a ferroelectric synaptic transistor, the weight update can be modulated by adjusting the applied voltage. The voltage pulse train should be carefully optimized to improve the learning accuracy and reduce programming energy consumption. In this study, we investigated the learning accuracy of neuromorphic computing based on the characteristics of synaptic devices and the program energy consumption according to pulse programs. We demonstrated changes in the analog conductance characteristics of ferroelectric thin‐film transistors by varying the pulse program for synaptic plasticity, discussed the characteristics for improving learning accuracy, and compared the programming energy consumption according to the pulse programs. We proposed a logarithmic‐incremental‐step pulse program that reduces programming energy consumption and improves learning accuracy.

We explore Exceptional Points (EPs) within a one-dimensional quasiperiodic Octonacci optical waveguide network. This network consists of segments, each composed of two-material subsegments featuring gain and loss materials, creating a parity-time-symmetric structure. We investigate the trend of EPs across generations 3 to 7 of the Octonacci sequence using the generalized eigenfunction method and transfer matrix method. Our findings reveal that as generations progress, band gaps become more pronounced, and the number of EPs significantly increases within these gaps. In particular, the third generation only supports unidirectional transparency. Bidirectional transparency appears in the fourth generation and becomes more pronounced in later generations. Coherent perfect absorption-lasing points are first seen in the seventh generation. These findings have implications for the design of all-optical devices and wideband and/or narrowband optical filters.

Metalenses, characterized by their discontinuous local phase shifts, are optically analogous to macroscopic curved lenses but are flat and scaled down to micrometer dimensions. Their compactness and compatibility with semiconductor manufacturing processes facilitate monolithic integration into existing optical devices. Here, we report on the integration of metalenses with micro light-emitting diodes (μ-LEDs), resulting in enhanced extraction efficiency and directionality. The metalenses were composed of identical nanohole units, each 150 nm in diameter, strategically arranged to induce desired local phase shifts at specific coordinates by varying the density of these units. Both simulated and experimental results demonstrated that these easy-configuration metalenses effectively focused a plane wave at a predetermined spot and collimated a diverging light source at the focal spot, exemplifying optical reciprocity. When integrated with ultraviolet (λ = 390 nm) 60 μm-sized μ-LEDs, the metalenses significantly improved device performance, exhibiting a 338% enhancement in peak intensity and a ±8° reduction in beam divergence compared to an unpatterned μ-LED. We believe that metalens-integrated μ-LEDs with high brightness, directionality, and resolution are optimally suited for near-eye applications, including virtual reality and augmented reality displays.

This study investigates the long-term thermal stability (4 h at 300 °C) of active contacts in high electron mobility transistor (HEMT) devices with and without 10 nm-target thickness chemical vapor deposition (CVD) carbon (C) layers, utilizing in-situ resistance measurements. The thermal stability of the HEMT devices was investigated over the temperature range of 150–300 °C, employing sputtered 30 nm Ti/150 nm Al/30 nm Ti/30 nm TiN (top) with Ohmic metal structures. The results indicate that the HEMT devices with the about 10 nm-thick CVD C layer exhibit superior long-term thermal stability compared to those without the CVD C layer, maintaining Ohmic contact behavior throughout the duration of the test. The increase in contact resistance without C films was 2 %, whereas with the C films, it was only 0.5 % after the 4 h-long thermal stability test at 300 °C.

The spin-orbit correlation in ferromagnet (FM) is an important factor that affects the orbital torque efficiency in the FM. We investigate the spin-orbit correlation in FM alloys, ${\text{Co}}_x{\text{Fe}}_{1-x}$ and ${\text{Ni}}_x{\text{Fe}}_{1-x}$, with varying their composition. We find spots where the spin-orbit correlation is significantly strong near the Fermi surface in ${\text{Co}}_{0.125}{\text{Fe}}_{0.875}$, ${\text{Co}}_{0.25}{\text{Fe}}_{0.75}$, ${\text{Co}}_{0.875}{\text{Fe}}_{0.125}$, and ${\text{Ni}}_{0.5}{\text{Fe}}_{0.5}$, while no such spot appears in ${\text{Co}}_{0.5}{\text{Fe}}_{0.5}$, and ${\text{Ni}}_{0.75}{\text{Fe}}_{0.25}$. These results imply that in the former structures, the orbital polarized current injected into these spots can provide a strong torque to the magnetization of the FM through the orbital torque mechanism. These results also show that even in the same alloy system, the difference in alloy composition can lead to different orbital torque efficiency.

In advancing photovoltaic technology, optimizing the metallization process is crucial for balancing electrical conductivity and optical performance in solar cell fabrication. This process directly impacts the efficiency and quality of solar cells, traditionally measured by the fill factor (FF). Historically, efforts have focused on evolving metal contacts to reduce optical shading and series resistance, which degrade solar cell efficiency. Our study enhances n-type Tunnel Oxide Passivated Contact (n-TOPCon) solar cells by optimizing screen-printing metallization, particularly by examining the effects of squeegee speeds. Employing a mix of experimental and analytical methodologies, we aimed to identify optimal conditions that improve electrical and optical performance, thereby elevating cell efficiency. Our findings indicate that a squeegee speed of 170 mm/s substantially boosts solar cell performance, evidenced by a current density (J_sc) of 38.96 mA/cm², open-circuit voltage (V_oc) of 684.29 mV, fill factor (FF) of 78.77 %, and a power conversion efficiency (PCE) of 21.00 %. Further, dark I–V measurements confirmed a shunt resistance (R_sh) of 6.25 × 10⁶ Ω and a reduced series resistance (R_s) of 6.48 Ω, underscoring the significance of precise metallization in reducing resistive losses and enhancing efficiency. Future research will explore innovative materials and cutting-edge printing techniques beyond squeegee speed adjustments. The potential incorporation of nanomaterials and conducting polymers aims to refine the metallization process further, promising to push the boundaries of efficiency and cost-effectiveness. This progression is essential for advancing n-TOPCon solar cell development, setting new industry standards, and propelling the sustainable energy movement.

Dual-stage scanners can successfully increase the range of atomic force microscope (AFM) scanners in space and/or frequency by designing and constructing two nanopositioners with significant differences in static and dynamic characteristics. In such cases, the positioning signal has to be split to meet the displacement and frequency limitations of each stage. Without closed-loop displacement measurement sensors, linearizing images acquired using signals split in time and frequency can be challenging. A common method, often cumbersome and time consuming, uses inverse model-based feedforward compensation. In this work, we show that image-based linearization can be used to achieve acceptable results for raster scans acquired using dual-stage scanners. In particular, we apply the feedforward and image-based methods to our homemade dual-stage lateral scanner and high-speed AFM (HS-AFM) system. The acquired scans compare well for the two methods, indicating that image-based raster scan linearization can be used in place of inverse model-based feedforward approaches.

Silver telluride, Ag₂Te, was synthesized on various 2D templates of carbon nanotubes (CNT) and transition-metal dichalcogenides (WTe₂ and VTe₂) via hydrothermal synthesis. X-ray diffraction (XRD) and Raman spectroscopy revealed that Ag₂Te was synthesized on the 2D templates under optimal synthesis conditions. Differential scanning calorimetry (DSC) confirmed that the structural phase transition of Ag₂Te underwent endothermic and exothermic reactions at approximately 410 and 425 K, respectively. Among various metallic templates, a large amount of Ag₂Te has been synthesized on strongly acidic CNT. X-ray absorption near-edge structure (XANES) revealed that the chemical state of the metallic support influenced the electronic structure of the as-grown Ag₂Te on the metallic supports. Our findings demonstrated that the hybrid 2D catalysts with an appropriate 2D metallic template can be a promising strategy for achieving efficient catalysis.

Functionalized graphene and carbon nanotubes (CNTs) are widely recognized for their exceptional physical properties, which make them highly suitable for various applications. Although molecular dynamics (MD) simulations are essential for investigating the atomic-level interactions and transport phenomena in functionalized graphene and CNT systems, setting up these simulations remains complex and time-consuming. To streamline this process, we have developed a novel web application that automates the generation of MD simulation setups of functionalized graphene and CNT systems compatible with AMBER force fields and the Gromacs software. Key features include the creation of nanopores, functionalization with hydrogen, hydroxyl, and/or carboxylate groups, and the application of periodic boundary conditions to effectively simulate infinite structures. To facilitate the MD analysis of transport phenomena through nanopores, our web application offers an automated analysis tool that generates and visualizes three-dimensional local flux fields from MD trajectories. Overall, our web applications significantly enhance the accessibility and efficiency of MD simulations of functionalized graphene systems, particularly for nanopore applications. Our web applications are freely available at https://yoo.skku.edu/apps.