Search Results (110)

This work proposes a polarization-insensitive scalable wide-angle metasurface array for highly efficient ambient energy harvesting in the 5.8 GHz Wi-Fi band. Inspired by dipole antenna principles, we design an asymmetric planar orthogonal dipole-based metasurface featuring monolithic integration of Schottky diodes (HSMS-2860) at unit cell feed gaps. This novel direct-impedance-matching strategy eliminates conventional matching networks, reducing energy conversion losses while enabling 99% radiation-to-AC efficiency across all polarization angles at 5.8 GHz. The coplanar architecture interconnects metasurface unit cells via inductors, simultaneously establishing low-loss DC channels and suppressing RF leakage. Fabricated as a 5 × 5 array, the prototype achieves 77.9% peak RF-to-DC efficiency with polarization insensitivity at an incident power of 25 dBm. Furthermore, with incident powers of 15 dBm and 20 dBm, the proposed metasurface array attained RF-to-DC conversion efficiencies exceeding 40% and 60%, respectively. This result indicates that the array is capable of achieving high energy harvesting efficiency across a broad power range. This scalable, drill-free, and polarization-insensitive design demonstrates strong potential for harvesting ambient RF energy in real-world multipath environments. Full article

Reconfigurable antennas play a central role in next-generation wireless communication systems by enabling dynamic adaptation of operating frequency, radiation pattern, and polarization. Tunable metasurfaces have emerged as a powerful and compact approach to antenna reconfiguration, allowing electromagnetic wave manipulation through engineered, planar structures whose properties can be dynamically controlled. By embedding active devices or tunable materials within metasurface unit cells, antenna characteristics can be modified without altering the antenna geometry. This review provides a comprehensive overview of reconfigurable antennas enabled by tunable metasurfaces. We adopt a functionality-based classification that focuses on operating frequency, radiation pattern, polarization, and multifunction reconfiguration. An overview of major tunability technologies, including PIN diodes, varactors, MEMS, graphene and two-dimensional materials, and liquid crystal (LC) or phase-change materials, is first presented. Subsequently, metasurface-based reconfiguration strategies are discussed and compared for each antenna functionality, highlighting design principles, practical trade-offs, and limitations. The review concludes with an assessment of challenges and future research directions relevant to next-generation wireless communications and beyond. Full article

g-C₃N₄ has emerged as a promising metal-free semiconductor for optoelectronic applications due to its suitable bandgap, excellent stability, and low cost. However, enhancing its photoresponse efficiency in practical devices remains a challenge. In this work, a high-performance self-powered photodetector was developed using a g-C₃N₄/textured Si n-n heterojunction fabricated via a simple solution process. The device exhibits excellent diode characteristics with a rectification ratio of ~4.9 × 10² and an ideality factor of 1.41. It achieves broadband detection from 405 to 980 nm, a high responsivity of 3.2 A/W, a specific detectivity of 1.9 × 10¹⁴ Jones, and fast response speeds of 44/36 ms at 650 nm under zero bias. Significantly, the textured Si-based device shows approximately tenfold higher performance than its planar Si counterpart, owing to enhanced light absorption from the textured surface. The combination of excellent photoresponse and simple fabrication makes the g-C₃N₄/textured Si n-n heterojunction a promising candidate for low-cost, high-performance optoelectronic applications. Full article

This paper analyzes microstructural layout and electrical behavior of silicon nanowire-based Schottky diodes, for use as wide-domain temperature sensors. The employed nanostructured three-dimensional substrates provide larger contact areas and enable higher Schottky barrier heights, ultimately leading to a better operable temperature range. Two metal deposition techniques (Radio Frequency sputtering and Electron-beam evaporation) are used to fabricate experimental Schottky diode samples. Scanning electron microscopy, X-ray diffraction, and diffuse reflectance investigations are carried out in order to determine nanowire distribution and the influence of subsequent metal deposition. The analyses evince the formation of a slightly inhomogeneous contact. The findings are validated by a thorough electrical characterization over a wide temperature domain. Inhomogeneity models are used in order to determine the main device parameters and the bias regions where they can be used as precise temperature sensors. The sputtered sample exhibits the best sensitivity, between 1 and 1.4 mV/K, while excellent linearity (R² > 99.5%) is obtained for Electron-beam evaporated devices. Both types of silicon nanowire-based Schottky diode sensors have 100–500K operable ranges, much larger than planar counterparts. Full article

We report on the fabrication and characterization of InGaN-based ridge-waveguide laser diodes employing spin-on-glass (SOG) as the insulation and planarization layer. In contrast to conventional silicon dioxide (SiO₂) isolation deposited by PECVD, the SOG approach provides improved surface planarity, reduced processing complexity, and lower fabrication cost. The laser structures were grown on GaN substrates by MOCVD, with the active region consisting of In_0.11Ga_0.89N quantum wells. Following ridge formation and SOG deposition, an etch-back process was used to form the electrical contacts. We have demonstrated the formation of high-quality insulating surfaces with strong adhesion to the ridge sidewalls. When using a Ni protective layer, the fabricated devices exhibited favorable electrical and optical characteristics and achieved stable laser operation under both pulsed and continuous-wave conditions. These results indicate that the SOG-based insulation process represents a promising alternative for the scalable and cost-effective fabrication of InGaN laser diodes targeting advanced photonic applications. Full article

Although various phosphorescent organic light-emitting diodes (PhOLEDs) have been developed, their lifetimes remain shorter than those of fluorescent OLEDs. In this study, a novel Pt(II) complex featuring a tetradentate ligand composed of bipyridine and phenoxypyridine, referred to as LL-O, was synthesized and fully characterized to evaluate its potential as a dopant for PhOLEDs. Geometry-optimized calculations indicate that LL-O adopts a distorted square–planar structure around the Pt(II) center. The complex displays bluish-green emission with maxima at 490 and 518 nm. However, it exhibits a low photoluminescence quantum yield (4%), primarily due to a dominant non-radiative decay rate that surpasses the radiative decay rate. Natural transition orbital analysis reveals that the emission of LL-O originates from a combination of triplet ligand-centered (³LC), triplet ligand-to-ligand charge-transfer (³LL′CT), and triplet metal-to-ligand charge-transfer (³MLCT) transitions. This compound also demonstrates high thermal stability (decomposition temperature > 340 °C) and an appropriate HOMO energy level (−5.58 eV), making it suitable for use as a dopant in versatile PhOLEDs. Full article

The rapid expansion of broadband wireless communication systems, including 5G, satellite networks, and next-generation IoT platforms, has created a strong demand for antenna architectures capable of real-time beam control, compact integration, and broad frequency coverage. Traditional reflectarrays, while effective for narrowband applications, often face inherent limitations such as fixed beam direction, high insertion loss, and complex phase-shifting networks, making them less viable for modern adaptive and reconfigurable systems. Addressing these challenges, this work presents a novel wideband planar metasurface that operates as a polarization rotation reflective metasurface (PRRM), combining 90° polarization conversion with 1-bit reconfigurable phase modulation. The metasurface employs a mirror-symmetric unit cell structure, incorporating a cross-shaped patch with fan-shaped stub loading and integrated PIN diodes, connected through vertical interconnect accesses (VIAs). This design enables stable binary phase control with minimal loss across a significantly wide frequency range. Full-wave electromagnetic simulations confirm that the proposed unit cell maintains consistent cross-polarized reflection performance and phase switching from 3.83 GHz to 15.06 GHz, achieving a remarkable fractional bandwidth of 118.89%. To verify its applicability, the full-wave simulation analysis of a 16 × 16 array was conducted, demonstrating dynamic two-dimensional beam steering up to ±60° and maintaining a 3 dB gain bandwidth of 55.3%. These results establish the metasurface’s suitability for advanced beamforming, making it a strong candidate for compact, electronically reconfigurable antennas in high-speed wireless communication, radar imaging, and sensing systems. Full article

A 4H-silicon carbide (SiC) trench gate metal–oxide–semiconductor field-effect transistor (MOSFET) with dual integrated Schottky barrier diodes (SBDs) was characterized using numerical simulations. The advantage of three-dimensional stacked integration is that it allows the proposed structure to obtain an electric field of below 0.6 MV/cm in the gate oxide and SBD contacts and achieve ~10% lower forward voltage of SBDs than the planar gate SBD-integrated MOSFET (PSI-MOS) and the trench gate structure with three p-type-protecting layers (TPL-MOS). The dual-SBD-integrated MOSFET (DSI-MOS) also highlights the better influences of the more than 70% reduction in the miller charge, as well as the over 50% reduction in switching loss compared to the others. Furthermore, the short-circuit (SC) robustness of the three devices was identified. The DSI-MOS attains the critical energy and the aluminum melting point in a longer SC time interval than the TPL-MOS. The p-shield layers in the DSI-MOS are demonstrated to yield the huge benefit of improving the reliability of the contacts when SC reliability is considered. Full article

This study introduces an organic light-emitting diode (OLED) light extraction method using a wavy-patterned polydimethylsiloxane (PDMS) substrate created via oxygen (O₂) plasma treatment. A rapid fabrication process adjusted the flow, pressure, duration, and power of the O₂ plasma treatment to replicate the desired wavy structure. This method allowed the treated samples to maintain over 90% total transmittance and enabled controlled haze adjustments from 10% to 70%. Finite-difference time-domain (FDTD) simulations were employed to determine optimal amplitudes and periods for the wavy structure to maximize optical performance. Further experiments demonstrated that bottom-emitting green fluorescent OLEDs constructed on these substrates achieved an external quantum efficiency (EQE) of 3.5%, representing a 97% improvement compared to planar PDMS OLEDs. Additionally, color purity variation was minimized to 0.044, and the peak wavelength shift was limited to 10 nm, ensuring consistent color purity and intensity even at wide viewing angles. This study demonstrates the potential of this cost-effective and efficient method in advancing high-quality display. Full article

Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. However, the electrical properties of bow-tie diodes are highly dependent on the purity of the grown epitaxial layer—specifically, the minimal number of defects—and the quality of the ohmic contacts. The quality of MBE-grown semiconductor structure depends on the presence of a buffer layer between a semiconductor substrate and an epitaxial layer. In this paper, we present an investigation of the electrical and optical properties of planar bow-tie microwave diodes fabricated using modulation-doped semiconductor structures grown via the MBE technique, incorporating either a GaAs buffer layer or a GaAs–AlGaAs super-lattice buffer between the semi-insulating substrate and the active epitaxial layer. These properties include voltage sensitivity, electrical resistance, I–V characteristic asymmetry, nonlinearity coefficient, and photoluminescence. The investigation revealed that the buffer layer, as well as the illumination with visible light, strongly influences the properties of the bow-tie diodes. Full article

A novel planar silicon carbide (SiC) MOSFET integrated with both MOS-channel diode (MCD) and junction barrier Schottky diode (JBS) on the same chip (MCD-JBSFET) is proposed and investigated through Technology Computer-Aided Design (TCAD) simulations in this paper. The proposed device features the lowest turn-on voltage and the best current conduction capability under the reverse-biased conditions, allowing it to achieve the same reverse conduction capability with fewer MCDs compared to conventional MOSFET with MCD structures (MCDFET). This reduction in the number of MCDs enables more channels to operate under forward-biased conditions, thereby improving power density. Compared to a conventional MOSFET integrated with JBS structure (JBSFET), the reverse current in the MCD-JBSFET flows through both the MCD and JBS, which suppresses the peak lattice temperature at Schottky contact and enhances the high-temperature robustness, especially under surge current conditions. In addition, the split-gate structure in the proposed structure optimizes the reverse capacitance and the figure of merit R_on,sp × Q_g by factors of 0.65 and 2.15, respectively. Finally, the switching losses are reduced by 40.2%, indicating the suitability of MCD-JBSFET for high-frequency and high-current applications. Full article

Simultaneous illumination and communication using solid-state lighting devices like white light-emitting diode (LED) light sources is gaining popularity. The white light LED comprises a single-colored yellow phosphor excited by the blue LED chip. Therefore, color-quality determining parameters like color-rendering index (CRI), correlated color temperature (CCT), and CIE 1931 chromaticity coordinates of generic white LED sources are poor. This article presents the development of multi-color phosphors excited by a blue LED to improve light quality and bandwidth. A multi-layer stacking of phosphor layers excited by a blue LED led to the quenching of photoluminescence (PL) and showed limited bandwidth. To solve this problem, a lens-free, electrically powered, broadband white light source is designed by mounting multi-color phosphor LEDs in a co-planar ring-topology. The CRI, CCT, and CIE 1931 chromaticity coordinates of the designed lamp (DL) were found to be 90, 5114 K, and (0.33, 0.33), respectively, which is a good quality lamp for indoor lighting. CRI of DL was found to be 16% better than that of white LED (WL). Assessment of visible light communications (VLC) feasibility using the DL includes time interval error (TIE) of data pattern or jitter analysis, eye diagram, signal-to-noise ratio (SNR), fast Fourier transform (FFT), and power spectral density (PSD). DL transmits binary data stream faster than WL due to a reduction in rise time and total jitter by 31% and 39%, respectively. The autocorrelation function displayed a narrow temporal pulse for DL. The DL is beneficial for providing high-quality illumination indoors while minimizing PL quenching. Additionally, it is suitable for indoor VLC applications. Full article

Low light extraction efficiency (LEE) remains a critical bottleneck in the performance of contemporary micro-light-emitting diodes (micro-LEDs). This study presents an innovative approach to improve the LEE of Gallium nitride (GaN)-based thin-film flip-chip (TFFC) micro-LEDs by integrating an inclined sidewall with photonic crystals (PhCs). Three-dimensional finite-difference time-domain (FDTD) simulations reveal that the inclined sidewall design significantly increases the escape probability of light, thereby improving LEE. Additionally, the PhCs’ structure further improves LEE by enabling more light to propagate into the escape cones through diffraction. Optimal results are achieved when the inclined sidewall angle (θ) is 28° and the PhCs exhibit a period (a) of 220 nm, a filling factor (f) of 0.8, and a depth (d) of 3 μm, resulting in a maximum LEE of 36.47%, substantially surpassing the LEE of conventional planar TFFC micro-LEDs. These results provide valuable design guidelines for the development of high-efficiency GaN-based micro-LEDs. Full article

The study developed a large emission area of flexible blue organic light-emitting diodes (BOLED) on a polyethylene terephthalate/ Indium tin oxide (PET/ITO) substrate using a polycyclic skeleton ν-DABNA Thermally Activated Delayed Fluorescence (TADF) material. Initially, a 1 × 1 cm² blue OLED was fabricated to optimize the layer thickness. The blue OLED structure consisted of PET/ITO/HATCN/TAPC/UBH-21:ν-DABNA/TPBi/LiF/Al. However, as the emission area increased to 3.5 × 3.5 cm², the current density decreased due to the resistance of PET/ITO, leading to luminance non-uniformity. To address this issue, auxiliary Au lines were added to the ITO anode to enhance current injection. Despite this, when the Au lines reached a thickness of 30 nm, average light emission was disrupted. To improve the luminescence characteristics of large-area PET/ITO OLEDs, a capping and planarization layer of PEDOT:PSS was applied. Grid uniformity revealed a significant increase in overall luminance uniformity from 74.1% to 87.4% with the addition of auxiliary Au lines. Further increases in grid line density slightly reduced uniformity but enhanced brightness, resulting in brighter, flexible, large-area blue OLED lighting panels. Full article

In this study, metal–silicide-based contacts to GaN-cap/AlGaN/AlN-spacer/GaN-on-Si heterostructure were investigated. Planar Schottky diodes with Cu-covered anodes comprising silicide layers of various metal–silicon (M–Si) compositions were fabricated and characterized in terms of their electrical parameters and thermal stability. The investigated contacts included Ti–Si, Ta–Si, Co–Si, Ni–Si, Pd–Si, Ir–Si, and Pt–Si layers. Reference diodes with pure Cu or Au/Ni anodes were also examined. To test the thermal stability, selected devices were subjected to subsequent annealing steps in vacuum at incremental temperatures up to 900 °C. The Cu/M–Si anodes showed significantly better thermal stability than the single-layer Cu contact, and in most cases exceeded the stability of the reference Au/Ni contact. The work functions of the sputtered thin layers were determined to support the discussion of the formation mechanism of the Schottky barrier. It was concluded that the barrier heights were dependent on the M–Si composition, although they were not dependent on the work function of the layers. An extended, unified Schottky barrier formation model served as the basis for explaining the complex electrical behavior of the devices under investigation. Full article