Device Structure Research Articles

Stability analysis of an axially moving viscoelastic beam under transverse magnetic fields and thermal loads

Slender flexible structures in electronic devices and spacecraft usually operate in complex thermal and magnetic environments, in which the stability is greatly affected by the complex environments. In this paper, an analytical method is proposed to study the stability of an axially moving viscoelastic beam under transverse magnetic fields and thermal loads. Firstly, the nonlinear control equation of the axially moving viscoelastic beam is derived by using Hamilton principle, in which the effects of the thermal loads, magnetic field variations and nonlinear deformation of the beam are considered based on the principle of magnetoelasticity. Secondly, Galerkin's method was applied to the derived continuous model to obtain the discrete differential equations of each vibrating mode. Finally, the incremental harmonic balance (IHB) method was employed to determine the unstable regions in the parameter space. The influences of the thermal load, axially moving velocity of the beam, viscosity coefficient, and magnetic field intensity on the regions of stability are investigated. It is found that the thermal loads, axially moving velocity and magnetic field intensity exert a significant influence on the unstable region. The derived results take into account of the combined effects of magnetic field and thermal variation, which is beneficial in understanding the stability of axially moving beams under complex magnetic and thermal environment.

Active Surface Passivation for mesa type short-wave infrared InGaAs Photodetectors

We propose a gate-controlled device structure for mesa-type infrared photon detectors with the means of improving surface conditions. Additional terminal added to the pn-junction allows surface charges to be manipulated by applying a constant E-field through a metal oxide semiconductor (MOS) structure. Short-wave infrared (SWIR) Indium Gallium Arsenide (InGaAs) sample with a cut-off wavelength of 1.69 μm is characterized. A theoretical framework is provided to gating mechanism. Experimental results show that, the shunt component of the dark current improved as high as 63% by interrupting the channel formation on the surface. Further improvements in the generation–recombination (GR) current is noted at more than 90% at 300 K. The effective GR lifetime of 20 μs is obtained under 50 V/μm surface-gate bias.

Dark Current Suppression in Two‐dimensional Histamine Lead Iodine Perovskite Single Crystal for X‐ray Detection and Imaging

AbstractLead halide perovskites have emerged as attractive X‐ray detector materials, owing to properties such as strong X‐ray stopping power, excellent carrier transport, and high sensitivity. Additionally, they can be easily prepared by using solution‐based synthesis approaches. However, traditional 3D (three‐dimensional) perovskites X‐ray detectors have shown limited application due to high dark currents generated under bias voltage as a result of strong ion migration. In this work, an X‐ray detector with a vertical structure device is demonstrated using 2D (two‐dimensional) histamine lead halide perovskite single crystal HAPbI4 (HPI, HA = histamine). Due to the dielectric screening effect of diamine and the vertical structure of the HPI device, the fabricated detector shows a sensitivity of 7737 µC Gyair−1 cm−2 under a bias voltage of 30 V. Furthermore, the detector shows a sensitivity of 293 µC Gyair−1 cm−2 and detection limit of 51.38 nGyair s−1 without bias voltage, wherein the dark current is almost completely suppressed. All of these properties indicate the X‐ray detection device is a promising candidate for next‐generation optoelectronic applications.

Efficient and Stable Quantum‐Dot Light‐Emitting Diodes with Trilayer PIN Architecture

AbstractAlthough the performance of quantum dot light‐emitting diodes (QLEDs) has been greatly improved in recent years, the multilayer device structure has become increasingly complex, limiting the practical application of QLEDs. Here, a novel trilayer PIN QLED with only three functional layers, which are Spiro‐OMeTAD:TFB bulk‐heterojunction (BHJ) hole transport layer (HTL), quantum‐dot emitting layer and ZnMgO electron transport layer is demonstrated. Due to the enhanced hole injection capability and suppressed electron leakage of Spiro‐OMeTAD:TFB BHJ HTL, the trilayer PIN QLED can show an excellent external quantum efficiency (EQE) of 25.1% and an impressive brightness of 299300 cd m−2 at only 8 V, which are significantly higher than those of conventional QLED. Moreover, the device stability is also remarkably improved due to the mitigation of hole accumulation and removal of unstable PEDOT:PSS. By using liquid alloy EGaIn as cathode, a fully solution‐processed vacuum‐free trilayer PIN QLED with a higher EQE of 27.3% can be further realized. The developed trilayer PIN QLEDs, with better performance and fewer functional layers, can promote the commercialization of QLED technology.

Performing hardness classification using diffusive memristor based artificial neurons

Abstract Artificial neurons and synapses are the building blocks for constructing a neuromorphic system such as Spiking Neural Network (SNN) or Artificial Neural Network (ANN). Recently, there has been tremendous interest in using memristors to develop neuromorphic technologies that can be used in advanced SNNs and ANNs. Memristors, because of their simple device structure, easy and high-density fabrication, and integration with other semiconductor electronics are suitable candidates for the construction of neuromorphic concepts. However, not much has been discussed about using memristors for the development of sensors that can be utilized for object- classification especially their rigidity, shape and structure. In this article, we propose the application of memristors, specifically silver nanoparticle based diffusive memristor, in conjunction with a piezoelectric sensor within a robotics gripper, serving as one receptor (a tactile sensor) that triggers neuron circuitry with memristors to generate spikes. Furthermore, to perform hardness classification, we utilized various objects to collect data and generated multiple spikes corresponding to each object. This data was then utilized with a machine learning algorithm. The outcomes were compared with the accuracy of commercial FSR tactile sensors. Our approach demonstrated the capability of diffusive memristors in generating neuron spikes from tactile stimuli for hardness classification, achieving accuracy ranging from 82% to 100% during the validation of 20% test data across various algorithms, while the FSR sensors achieved an accuracy range of 95% to 98%.

Application of machine learning for detecting and tracking turbulent structures in plasma fusion devices using ultra fast imaging.

This study explores the application of machine learning techniques for detecting and tracking plasma filaments around the boundary of magnetically confined tokamak plasmas. Plasma filaments, also called blobs, are responsible for enhanced turbulent transport across magnetic field lines, and their accurate characterization is crucial for optimizing the performance of magnetic fusion devices. We present a novel approach that combines machine learning methods applied to data obtained from ultra-fast cameras, including YOLO (You Only Look Once) for object detection, semantic segmentation, and specific tracking methods. This approach enables fast and accurate detection and tracking of filaments while overcoming the limitations of conventional methods, which are time-consuming and prone to human subjectivity. A significant advance in our study lies in the development of a method for automatically labeling a large batch of data, which greatly facilitates the training of supervised machine learning algorithms. Using these techniques, we obtained promising results demonstrating a significant improvement over conventional tracking methods, achieving a detection accuracy of up to 98.8%, while reducing the inference time per frame by 15% to 31% compared to conventional Kalman filter tracking. These results open up new perspectives for investigating turbulent phenomena in tokamaks, and could have important implications for the development of controlled nuclear fusion.

Ultrasensitive, Fast-Response, and Stretchable Temperature Microsensor Based on a Stable Encapsulated Organohydrogel Film for Wearable Applications.

Ionic conductive hydrogel-based temperature sensors have emerged as promising candidates due to their good stretchability and biocompatibility. However, the unsatisfactory sensitivity, sluggish response/recovery speed, and poor environmental stability limit their applications for accurate long-term health monitoring and robot perception, especially in extreme environments. To address these concerns, here, the stretchable temperature sensors based on a double-side elastomer-encapsulated thin-film organohydrogel (DETO) architecture are proposed with impressive performance. It is found that the water-polyol binary solvent, organohydrogel film, and sandwiched device structure play important roles in the temperature sensing performance. By modifying the composition of binary solvent and thicknesses of organohydrogel and elastomer films, the DETO microsensors realize a thickness of only 380 μm, unprecedented temperature sensitivity (37.96%/°C), fast response time (6.01 s) and recovery time (10.53 s), wide detection range (25-95.7 °C), and good stretchability (40% strain), which are superior to those of conventional hydrogel-based sensors. Furthermore, the device displays good environmental stability with negligible dehydration and prolonged operation duration. With these attributes, the wearable sensor is exploited for the real-time monitoring of various physiological signals such as human skin temperature and respiration patterns as well as temperature perception for robots.

Design and research of high voltage β-Ga2O3/4H-SiC heterojunction LDMOS

Abstract In recent years, gallium oxide (Ga2O3), one of the ultra-wide band-gap semiconductor materials, has been regarded as one of the most promising materials in the field of high-voltage and high-power electronic devices in the future because of its unique electrical properties and low preparation cost. However, it is difficult for β-Ga2O3 materials to form effective P-type doping, so the PN junction is not formed in most of its power devices, which greatly limits the improvement of its voltage resistance. A novel lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOS) is proposed to realize a junction β-Ga2O3 power device and improve the voltage resistance performance of β-Ga2O3 power devices. In this device, a β-Ga2O3 power device with a junction is realized by using P-type 4H-SiC to form a PN junction with N-type β-Ga2O3, and the voltage resistance of the β-Ga2O3 power device is improved. Sentaurus TCAD software was used to simulate the device structure and electrical performance. The device is optimized by adjusting the length of the drift zone, drift zone concentration, SiC channel concentration, and gate oxide thickness. Optimized, the device exhibits a positive threshold voltage of 3.42 V, a breakdown voltage of 2203 V, a specific on-resistance of 7.80 mΩ·cm2, and a power figure of merit of 622 MW cm−2. The results show that the heterojunction device is significant for realizing high-performance junction β-Ga2O3 power devices.

A Combination of Silver Nanowires and Al2O3 to Replace ITO and MgF2 in a Cu(In,Ga)Se2 Thin‐Film Solar Cell

AbstractSilver nanowire (AgNW) transparent conducting electrodes can be prepared via a low‐cost process and deliver optoelectronic performance comparable to or even better than that of indium tin oxide (ITO). However, their integration into a real device is challenging, mainly because of the weak adhesion between AgNWs and the underlayer. Furthermore, when AgNWs replace ITO, a different material needs to be considered for the antireflection coating (ARC) of a thin‐film solar cell. A combination of AgNWs and Al2O3 is employed to replace both ITO and the MgF2 in a Cu(In,Ga)Se2 (CIGS) thin‐film solar cell. The quality of the contact between the AgNWs and CdS buffer is improved by introducing a chemical‐bath‐deposited welding layer, which improves the fill factor of the cell from 43.4% to 68.7%. Accordingly, the exposed surface of the CIGS thin‐film solar cell changes from ITO to CdS. Therefore, the commonly used MgF2 ARC is replaced with Al2O3, which is a better match in terms of the refractive index for AgNW‐based CIGS thin‐film solar cells. The adoption of the Al2O3 ARC increases the short‐circuit current density of the cell by 7.3%. In conclusion, a device structure of Al2O3/AgNW/CdS/CIGS/Mo is suggested for CIGS thin‐film solar cells.

Advances in Organic Materials for Next-Generation Optoelectronics: Potential and Challenges

This review provides a comprehensive overview of recent advancements in the synthesis, properties, and applications of organic materials in the optoelectronics sector. The study emphasizes the critical role of organic materials in the development of state-of-the-art optoelectronic devices such as organic solar cells, organic thin-film transistors, and OLEDs. The review further examines the structure, operational principles, and performance metrics of organic optoelectronic devices. Organic materials have emerged as promising candidates due to their low-cost production and potential for large-area or flexible substrate applications. Additionally, this review highlights the physical mechanisms governing the optoelectronic properties of high-performance organic materials, particularly photoinduced processes relevant to charge carrier photogeneration. It discusses the unique benefits of organic materials over traditional inorganic materials, including their light weight, simple processing, and flexibility. The report delves into the challenges related to stability, scalability, and performance, while highlighting the wide range of electronic properties exhibited by organic materials, which are critical for their performances in optoelectronic devices. Furthermore, it addresses the need for further research and development in this field to achieve consistent performance across different types of devices.

Pursuing high-fidelity control of spin qubits in natural Si/SiGe quantum dot

Electron spins in silicon quantum dots are a promising platform for fault-tolerant quantum computing. Low-frequency noise, including nuclear spin fluctuations and charge noise, is a primary factor limiting gate fidelities. Suppressing this noise is crucial for high-fidelity qubit operations. Here, we report on a two-qubit quantum device in natural silicon with universal qubit control, designed to investigate the upper limits of gate fidelities in a non-purified Si/SiGe quantum dot device. By employing advanced device structures, qubit manipulation techniques, and optimization methods, we have achieved single-qubit gate fidelities exceeding 99% and a two-qubit controlled-Z (CZ) gate fidelity of 91%. Decoupled CZ gates are used to prepare Bell states with an average fidelity of 91%, typically exceeding previously reported values in natural silicon devices. These results underscore that even natural silicon has the potential to achieve high-fidelity gate operations, particularly with further optimization methods to suppress low-frequency noise.

Analysis on future development of solar cells focusing on materials and devices

In recent times, solar cells have garnered significant attention due to their numerous advantages. These include continuously improving energy conversion efficiency, a simple solution preparation method, flexibility, lightweight design, wearability, suitability for ultra-lightweight space applications, and low-cost material components. Perovskite solar cells have achieved impressive efficiencies of over 25% by using high-quality perovskite films synthesized at low temperatures and by making advancements in compatible interface and electrode materials. Moreover, the stability of cells has become a major focus of research. This paper analyzes the development history, material system, device structure, challenges, and future development direction of perovskite solar cells. The unique photoelectric properties and tunable band gap of materials have made them a hot topic in the field of solar cells. In this paper, the basic characteristics and synthesis methods of perovskite materials are introduced before discussing the device structure, interface engineering, and stability of perovskite solar cells in detail. Finally, it prospects on the future development trend of perovskite solar cells.

Impact of graded CIGS absorber layer on Cd-free CIGS thin-film solar cell performance: numerical optimization

Abstract This paper investigates replacing the CdS buffer layer with (Zn, Mg)O and Zn(S, O) double buffer layers. To increase the efficiency of the structure, our strategy involves numerically studying and comparing three types of CIGS bandgap absorber layers: FB (Flat Band), Double Gradient Bandgap (DG) with a high bandgap near the Mo contact (back side), a low bandgap near the buffer layer (front side), and a minimum bandgap between them, and Simple Gradient Bandgap (SG) with a high bandgap near the Mo contact (back side) and a low bandgap near the buffer layer (front side). Each type features different linear graded profiles in the thickness direction to determine the optimal bandgap gradient of the CIGS layer. The performance of the three types is numerically analyzed using the SCAPS-1D simulator. Simulation enables us to test multiple structural combinations efficiently, saving both time and money, while providing results that guide experimental research. The proposed device structure is composed of the following layers: ZnO:Al/n-Zn1-xMgxO/n- ZnSxO1-x/p- Graded-CuIn1-xGaxSe2 /Mo. To study the effects of linear bandgap gradient distribution of Ga⁄((Ga+In) ) ratio according to the thickness direction on CIGS solar cell performance, the electrical properties of the proposed CIGS model were initially matched with experimental data to confirm the structure's accuracy. It was found that the Double Gradient Bandgap (DG), with maxima of 1.44 eV at the back side (near Mo contact), 1.238 eV at the front side (near n-type buffer layer interface), and a minimum of 1.154 eV at a position of 1.7 µm from the back side, has a higher efficiency than the other structures with 26.22% (Voc = 0.8134 V, Jsc = 37.82 mA/cm², FF = 85.21%). Optimizing the bandgap gradient of the CIGS absorber layer helps improve the efficiency of CIGS solar cells. 

TCAD simulation on an UACCUFET inserted with 3C/4H–SiC hetero-crystalline junctions for accumulation-channel and fly-back

Due to high channel mobility, SiC accumulation-channel field-effect transistors (ACCUFETs) exhibit important research and application values in high-frequency and large-power fields, but still encounter poor reverse recovery, etc. An enhancement-mode U-shaped gate ACCUFET integrated with 3C/4H–SiC hetero-crystalline junctions (HCJs) and semi-super-junction (SSJ) is constructed, where a (n−)4H–SiC-layer in (n)3C–SiC/(n−)4H–SiC HCJ is adopted to form accumulation-channel for conduction due to field-effect, another HCJ composed of (n)3C–SiC and (n)4H–SiC drift region is employed for fly-back under low cut-in voltage (VF) to shorten reverse recovery time (trr). Additionally, a SSJ is used to raise the breakdown voltage (VB). The device structure and performance are optimized by the Silvaco TCAD, which illustrates the values of VB and static figure of merit (FOMHM) are increased by 15.6 % and 5.6 % respectively compared to those of the counterpart with Schottky barrier diode. This paper can provide new ideas for devising high-performance ACCUFETs.

Sensitive Self-Driven Single-Component Organic Photodetector Based on Vapor-Deposited Small Molecules.

Typically, organic solar cells (OSCs) and photodetectors (OPDs) comprise an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high-performance devices but has several drawbacks for upscaling and stability. This study presents a fully vacuum-deposited single-component OPD, employing the neat oligothiophene derivative DCV2-5T in the photoactive layer. Free charge carriers are generated with an internal quantum efficiency of 20 % at zero bias. By optimizing the device structure, a very low dark current of 3.4 · 10-11Acm-2 at -0.1V is achieved, comparable to the dark current of state-of-the-art bulk heterojunction OPDs. This optimization results in specific detectivities of 1· 1013Jones (based on noise measurements), accompanied by a fast photoresponse (f-3dB = 200kHz) and a broad linear dynamic range (>150dB). Ultrafast transient absorption spectroscopy unveils that charge carriers are already formed at very short time scales (<1ps). The surprisingly efficient bulk charge generation mechanism is attributed to a strong electronic coupling of the molecular exciton and charge transfer states. This work demonstrates the very high performance of single-component OPDs and proves that this novel device design is a successful strategy for highly efficient, morphological stable and easily manufacturable devices.

Ultrafast reconfigurable direct charge trapping devices based on few-layer MoS2

Abstract Charge trapping devices incorporating 2D materials and high-κ dielectrics have emerged as promising candidates for compact, multifunctional memory devices compatible with silicon-based manufacturing processes. However, traditional charge trapping devices encounter bottlenecks including complex device structure and low operation speed. Here, we demonstrate an ultrafast reconfigurable direct charge trapping device utilizing only a 30 nm-thick Al2O3 trapping layer with a MoS2 channel, where charge traps reside within the Al2O3 bulk confirmed by transfer curves with different gate-voltage sweeping rates and photoluminescence (PL) spectra. The direct charging tapping device shows exceptional memory performance in both three-terminal and two-terminal operation modes characterized by ultrafast three-terminal operation speed (≈300 ns), an extremely low OFF current of 10-14 A, a high ON/OFF current ratio of up to 107, and stable retention and endurance properties. Furthermore, the device with a simple symmetrical structure exhibits VD polarity-dependent reverse rectification behavior in the high resistance state (HRS), with a rectification ratio of 105. Additionally, utilizing the synergistic modulation of the conductance of the MoS2 channel by VD and VG, it achieves gate-tunable reverse rectifier and ternary logic capabilities.

Effect of Iodine Doped Pentacene Thin Film on the Performance of Organic Light Emitting Diode

The study investigated the effect of iodine-doped pentacene film as a buffer layer in an organic light-emitting diode (OLED). In this study, an ITO (indium tin oxide)-based sample is used as a reference device for comparative purposes. In OLED devices, the buffer layers were deposited using the doping of iodine vapor with the pentacene materials under proper conditions. The thermal treatment of the doped pentacene film results in increasing the conductivity of the buffer layer. Surface morphology for the bilayer anode was carried out by FESEM (Field Emission Scanning Electron Microscope) analysis. In our work, maximum luminance of 2345 cd/m2 and current efficiency of 5.4 cd/A are obtained, along with more stability performance under annealing treatment in the device structure of FTO/iodine-doped pentacene (30 nm)/TPD [N, N′-Bis(3-methyl phenyl)-N, N′-diphenylbenzidine] (44 nm)/Alq3 [Tris(8-hydroxyquinoline)aluminum(III)] (52 nm)/LiF (lithium fluoride) (5 nm)/Al (aluminum) (110 nm).

Anomalous Nernst Effect-Based Near-Field Imaging of Magnetic Nanostructures.

The anomalous Nernst effect (ANE) gives rise to an electrical response transverse to magnetization and an applied temperature gradient in a magnetic metal. A nanoscale temperature gradient can be generated by the use of a laser beam applied to the apex of an atomic force microscope tip, thereby allowing for spatially resolved ANE measurements beyond the optical diffraction limit. Such a method has been previously used to map in-plane magnetized magnetic textures. However, the spatial distribution of the out-of-plane temperature gradient, which is needed to fully interpret such ANE-based imaging, was not studied. We therefore use a well-known magnetic texture, a magnetic vortex core, to demonstrate the reliability of the ANE method for imaging of magnetic domains with nanoscale resolution. Moreover, since the ANE signal is directly proportional to the temperature gradient, we can also consider the inverse problem and deduce information about the nanoscale temperature distribution. Our results together with finite element modeling indicate that besides the out-of-plane temperature gradients there are even larger in-plane temperature gradients. Thus, we extend the ANE imaging to study the out-of-plane magnetization in a racetrack nanowire by detecting the ANE signal generated by in-plane temperature gradients. In all cases, a spatial resolution of ≈70 nm is obtained. These results are significant for the rapidly growing field of thermoelectric imaging of antiferromagnetic spintronic device structures.

Giant Colloidal Quantum Dot/α-Ga2O3 Heterojunction for High Performance UV-Vis-IR Broadband Photodetector.

Broadband optoelectronics, which extend from the UV to IR regions, are crucial for imaging, autonomous driving, and object recognition. In particular, photon detection efficiency relies significantly on semiconductor properties, such as absorption coefficients and electron-hole pair generation rate, which can be optimized by designing a suitable p-n junction. In this study, we devise giant PbS colloidal quantum dots (G-PbS CQDs) that exhibit high absorption coefficients and broadband absorption. To leverage these exceptional optical properties, we combine G-PbS CQDs with an ultrawide-bandgap semiconductor, α-Ga2O3, and create an efficient G-PbS CQD/α-Ga2O3 heterojunction photodetector that exhibits high performance across the UVC-vis-NIR spectrum range. The resultant heterojunction facilitates efficient electron-hole pair separation at the G-PbS CQD/α-Ga2O3 heterojunction. Furthermore, we utilize transparent graphene electrodes to overcome the limitations of conventional transistor-type device structures and the substantial optical losses induced by opaque metal electrodes. This strategy maximizes the light-collection area and results in an approximately 3-orders of magnitude higher responsivity (55.5 A/W) and specific detectivity (1.66 × 1013 Jones) compared to devices with opaque metal electrodes.

Transparent Electrode‐Free Light‐Emitting Devices Exploiting Ion Transport‐Controlled Electrochemiluminescence

AbstractTransparent electrode‐free light‐emitting devices are presented that exploit electrochemiluminescence (ECL). These devices feature two side‐by‐side noble metal electrodes connected by an ECL active layer. The significance of bulk ion‐transport characteristics is investigated within the ECL active layer in producing uniform planar emission from the device. These characteristics can be enhanced by simply increasing the ECL active layer thickness or adding an ion gel electrolyte layer on top of the ECL active layer. The use of only electrochemically stable noble metal electrodes results in an operational lifetime exceeding 10 h, which is the longest lifetime reported for ECL‐based light‐emitting devices to date. The device structure based on ECL does not require transparent electrodes, allowing for increased flexibility when designing devices for future light‐emitting device applications.