Current Blocking Research Articles

Slotted surface gratings fabricated by selective area growth of the p-InP cladding layer for BH lasers.

In this paper, we present a novel, to our knowledge, method for the fabrication of slotted surface gratings for buried heterostructure (BH) lasers. In the device fabrication process, SiO2 strips needed for InP current blocking layer growth are reused for the formation of slot grating pattern masks. In the following growth of the p-InP cladding layer, because the slot areas are covered by SiO2, the InP material is grown selectively in only the areas outside the slot areas, forming slots of the surface gratings in the p-InP layer at the same time as the cladding layer growth. Single longitude mode BH lasers having slotted surface gratings have been fabricated successfully, and the spectra show higher than 40 dB side mode suppression ratio (SMSR). The adoption of the method helps to simply the device fabrication and thus lower the device fabrication cost notably.

Design and simulation of high performance β-Ga2O3 super barrier rectifier with a current blocking layer

In this work, a β-Ga2O3 super barrier rectifier with a current blocking layer (CSBR) is proposed. Its static characteristics, dynamic characteristics and surge capability are investigated by TCAD simulation. The Baliga’s figure of merit (BFOM) can reach 1.62 GW cm−2 with the on-resistance of 3.68 mΩ cm−2 and the breakdown voltage of 2447 V, exhibiting excellent performance. Foremost, the turn-on and turn-off of the device is controlled by metal-oxide-semiconductor (MOS) structure. The reverse recovery time is 11.2 ns, which is compatible with that of a Schottky diode. Simulation results show that the dimensions of the cells and the proportion of the ohmic contact region in the cells are the key parameters affecting the reverse recovery time. In addition, the CSBR with double-side cooling configuration demonstrates high surge capability. It can sustain a peak surge current density of 5000 A cm−2, which is more than 10 times its forward current (V Forward = 3.0 V). Overall, the proposed structure has a high BFOM, excellent reverse characteristics and high reliability, demonstrating its potential in high voltage applications. Moreover, CSBR can be embedded into Ga2O3-MOSFET as a free-wheeling diode.

Direct single-molecule detection of CoA-SH and ATP by the membrane proteins TMEM120A and TMEM120B.

Membrane proteins are vital resources for developing biosensors. TMEM120A is a membrane protein associated with human pain transmission and lipid metabolism, and recent studies have demonstrated its ability to transport ions and bind to coenzyme A (COA-SH), indicating its potential to develop into a single-molecule sensor based on electrical methods. In this study, we investigated the ion transport properties of TMEM120A and its homolog TMEM120B on an artificial lipid bilayer using single-channel recording. The results demonstrate that both proteins can fuse into the lipid bilayer and generate stable ion currents under a bias voltage. Based on the stable ion transport capabilities of TMEM120A and TMEM120B, as well as the feature of TMEM120A binding with COA-SH, we developed these two proteins into a single-molecule sensor for detecting COA-SH and structurally similar molecules. We found that both COA-SH and ATP can reversibly bind to single TMEM120A and TMEM120B proteins embedded in the lipid bilayer and temporarily block ion currents during the binding process. By analyzing the current blocking signal, COA-SH and ATP can be identified at the single-molecule level. In conclusion, our work has provided two single-molecule biosensors for detecting COA-SH and ATP, offering insights for exploring and developing bio-inspired small molecule sensors.

Significantly Enhanced the Energy Density of Dielectric Composites by Sandwich Structure with Highly Insulating Mica Nanosheets.

Dielectric polymer composites exhibit great application prospects in advanced pulse power systems and electric systems. However, the decline of breakdown strength by loading of single high dielectric constant nanofiller hinders the sustained increase in energy density of the composites. Here, a sandwich-structured nanocomposite prepared with mica nanosheets as the second filler exhibits decoupled modulation of dielectric constant and breakdown strength. The traditional layered clay mineral mica is exfoliated into nanosheets and filled into polyvinylidene difluoride (PVDF), which shows a special depolarization effect in the polymer matrix. In Kelvin probe microscopy characterization and thermally stimulated depolarization current indicates that the mica nanosheets provided space charge traps for the polymer matrix and effectively suppressed the carrier motion. A sandwich structure composite material with mica nanosheets as the central layer has achieved a high energy density of 11.48 Jcm-3, 2.4 times higher than the pure PVDF film. This is due to the fact that randomly oriented distribution of nanosheets in a polymer matrix provide better current blocking. This work provides an effective method to improve the energy density of dielectric polymer composites by synergistically introducing insulating nanosheets and high dielectric constant nanofillers.

(Poster Award - 1st Place) Emerging Effect of Vertical-Oriented WSe2 Interfacial Layers in the CIGSe Thin Film Solar Cells

Copper indium gallium selenide (CIGSe) thin film solar cells become popular due to their potential as a solution for green energy and space technology recently. These solar cells have a similar electrical performance to traditional silicon solar cells, making them ideal for light, flexible, and high-performance applications. Molybdenum is a popular material for the rear electrode due to its conductivity and low cost. During the selenizing process of the absorber layer, MoSe2 will be formed between Mo and CIGSe layer, which improves adhesion between Mo and CIGSe and facilitates carrier transport from the absorber layer to the rear electrode. Therefore, previous studies show that oxides or nitride-based materials, such as Titanium Nitride and Alumina, are used as the passivation layer at the back contact to address the trade-off of the critical thickness of the MoSe2 layer. That is, designing a nanostructure and creating a contact hole can attract carriers and avoid current blocking. Similarly, Oxide-based material interfacial layers, such as Molybdenum oxide and tungsten oxide, can also play a role in the obstacle of selenium diffusion and modify the band structure. In this work, a few layers of WSe2 interfacial layer were introduced between the CIGSe absorber layer and Mo electrode. First, 20 nm WOx was deposited on Mo by E-beam evaporation. Second, WOx was selenized by a vertical furnace with ICP coils plasma system to form WSe2. By tuning the substrate temperature of plasma-enhanced selenization process, the full vertically lamellar-oriented WSe2 was formed on Mo. The results show that inserting a few layers of WSe2 improved the efficiency of the CIGS solar cell from 12.5 to 14.3%, with a significant increase in short circuit current density up to 38mA/cm2. This improvement was attributed to the improved carrier transportation through the backside interface, facilitated by the specific vertically lamellar-orientated WSe2 and the induced Gallium gradient measured by TEM, SIMS, and XPS. The remarkable enhancement by WSe2 provides the potential for further applications. Figure 1

A novel triple capacitor multi-level submodule MMC topology with fault current clearing capability

In the high voltage direct current system based on modular multilevel converter (MMC-HVDC), the half-bridge submodule (HBSM) has become the preferred submodule for significant projects due to its convenient control and low cost. However, the DC short-circuit protection performance of MMC-HVDC will seriously restrict its development in areas such as overhead lines, high voltage, and large capacity. This article proposes a triple capacitor multi-level submodule (TCMSM) topology of modular multilevel converter with DC fault-blocking capability. It utilizes at least one-third of the module capacitance in the bridge arm to reverse to suppress DC fault current and turn off the diode. At the same time, the unidirectional conductivity of the diode can also prevent arc reignition at the fault point. The article also conducted in-depth research on the DC short-circuit fault elimination mechanism of this topology, and compared its performance with other topologies. Through analysis, it can be concluded that TCMSM reduces the initial investment and operating costs by reducing the number of devices inside the module while possessing the fault current blocking ability. Finally, MATLAB/Simulink was used to simulate and verify the proposed new topology, and its performance was analyzed.

Improvement of Power and Efficiency of High-Mesa Semi-Insulating InP: Fe Buried Heterostructure Lasers with Wide Bandgap Layers

High-mesa semi-insulating buried heterostructure (SIBH) lasers with InP: Fe have great potential in high-speed and high-power scenarios, but the leakage current problem under high current injections has always limited their application. In order to solve the issue of low output power and low efficiency for high-mesa SIBH lasers, the mechanism of leakage current generation in InP-based semi-insulating (SI) layers at high injection levels was analyzed through numerical simulation. The deterioration of the device performance is due to the hole current-induced electron leakage current, which results from the reduction of the potential barrier and Fe-Zn interdiffusion. Thus, lasers with wide bandgap layers of InAlAs and ZnCdSe were employed for current blocking, the power and wall-plug efficiency of which were improved by more than 36% and 5%, respectively. For the first time, a SIBH laser based on lattice-matched ZnCdSe barrier layers is proposed, which shows good output performance and high reliability. The introduction of the wide bandgap layer in the SIBH structure establishes potential barriers to confine both carrier leakages at high injection levels, which realizes the high-power and high-efficiency operation of the laser.

Electrical characteristics of in situ Mg-doped β-Ga2O3 current-blocking layer for vertical devices

The lack of p-type doping has impeded the development of vertical gallium oxide (Ga2O3) devices. Current blocking layers (CBLs) using implanted deep acceptors have been used to demonstrate vertical devices. This paper presents a pioneering demonstration of in situ Mg-doped β-Ga2O3 CBLs grown using metal–organic chemical vapor deposition. The Mg-doping density during growth was calibrated by quantitative secondary ion mass spectroscopy. Electrical test structures were designed with in situ Mg doped layers with various targeted Mg doping concentrations. The effectiveness of the CBL is characterized by using temperature-dependent current–voltage measurements using n-Mg-doped-n structures, providing crucial insight into the underlying mechanisms. Pulsed measurements show similar blocking characteristics as DC. To further validate the experimental results, a TCAD simulation is performed, and the electrically active effective doping is found to be dependent on the Mg-doping density, offering an alternate perspective on the optimization of CBL performance. Breakdown measurements show a peak 4 MV/cm field strength.

Simultaneous Recognition of Over- and Under-Expressed MicroRNAs Using Nanopore Decoding.

This paper describes a strategy for simultaneous recognition of over- and under-expressed microRNAs (miRNAs) using the method of signal classification-based nanopore decoding. MiRNA has attracted attention as a promising biomarker for cancer diagnosis owing to its cancer-type-specific expression patterns. While nanopore technology has emerged as a simple and label-free method to detect miRNAs and their expression patterns, recognizing patterns involving simultaneous over/under-expression is still challenging due to the inherent working principles. Here, inspired by the sequence design for DNA computation with nanopore decoding, we designed diagnostic DNA probes targeting two individual over/under-expressed miRNAs in the serum of oral squamous cell carcinoma. Through nanopore measurements, our designed probes exhibited characteristic current signals depending on the hybridized miRNA species, which were plotted on the scatter plot of duration versus current blocking ratio. The classified signals reflected the relative abundance of target miRNAs, thereby enabling successful pattern recognition of over/under-expressed miRNAs, even when using clinical samples. We believe that our method paves the way for miRNA-targeting simple diagnosis as a liquid biopsy.

The Most Effective Self-Sustaining Antitumor Responses Activated by anti-PD1 Antibody are Likely Mediated by PD1-Negative T Cells

Immune checkpoint inhibitor (ICI) therapy has transformed the battlefield of cancer therapy by showing some of the most dramatic and durable antitumor responses ever seen. Yet ICI therapy is only effective in a minority of cancer patients. Among responders, only a few of them demonstrated a durable and self-sustaining pattern of response. It would be desirable to repeat the most durable success of ICI therapy in as more cancer patients as possible. That requires the true understanding of the mechanism behind the therapy. In previous publication, we have pointed out that the current blocking model of how ICI therapy works is wrong in that it cannot explain some critical observations such as the trigger effect, the hyper-progression and the autoimmunity associated with the therapy. On the other hand, we have raised an alternative model based on the partial depletion of PD1-positive T cells and the subsequent homeostatic activation of remaining T cells. This model, which we call the depletion model, could explains all of the perplexing clinical observations mentioned above. It also predicts that under repeated administration of antibodies to PD1/PDL1, a common practice in the clinic, the surviving immune response must be mediated by PD1-nagative T cells. Since some of the most dramatic and durable responses to ICI therapy did not require antigen-releasing treatments (such a chemotherapy), they must be self-sustaining as well. Here, using real-world cases, we present evidence that the most effective and self-sustaining antitumor responses are likely mediated by PD1-nagative T cells, an observation supporting our depletion model for ICI therapy. This observation raises fundamental questions regarding the current clinical use of ICI therapy and points to a future direction for the search of ways to activate PD1-nagative T cells for antitumor response.

Postdeposition Halide Exchange for Achieving Deep-Blue Perovskite Light-Emitting Diodes: The Role of the Organic Cations in the Chloride Source.

Postdeposition halide exchange has been a popular strategy for tuning the emission wavelength of metal halide perovskites and is particularly attractive in achieving deep-blue perovskite light-emitting diodes (PeLEDs), where the quality of the emissive layer is largely limited by the low solubility of chlorides in perovskite precursor solution. In this work, the halide exchange strategy isexamined for deep-blue PeLEDs, with a focus on understanding the role of the organic cations of the halide salt (i.e., the chloride source for ion exchange) in modifying the properties of the perovskite films and consequently the PeLED performances. By comparatively investigating the treatment effects of two model systems, namely phenethylammonium chloride and 2,2-diphenylethylammonium chloride (DPEACl), it isfound that although the two chlorides produce highly similar photoluminescence properties of the perovskite films, they create different landscapes for current flow in the PeLEDs. In particular, the bulky branch-structured DPEA cations exhibit minimal disturbance to the perovskite grains while providing highly effective inter-grain void filling and thus leakage current blocking, leading to 3D perovskite-based PeLEDs with a record high peak external quantum efficiency of 6.4% at 462nm. The study highlights the importance of organic cation selection in the halide exchange processes for PeLEDs.

Cover Picture

Herein, a single molecule detection technology based on glass nanopore is established to analyze xylan dissolved in ionic liquid. The nanopore detection technology shows the structural difference of heterogenous branched chain and homogeneous straight chain based on the single characteristic current blocking signal and statistical information, providing a research basis for the structural analysis of water insoluble polysaccharides. More details are discussed in the article by He et al. on page 1720—1726.image

Application of Nanopore Single Molecule Detection Technology in Analysis of Xylan Dissolved in Ionic Liquid†

Comprehensive SummaryXylan is the most abundant hemicellulose in nature. As a new type of green organic solvent, ionic liquid shows good preservation ability for the functional groups of hemicellulose. In this paper, a single molecule detection technology based on glass nanopore was established to analyze xylan dissolved in ionic liquid. Arabino‐xylan (AX) and beech xylan (BX) are respectively taken as the representatives of heterogeneous xylan and homogeneous xylan. Firstly, unmodified glass nanopore was used to detect the dissolved xylan in ionic liquid, and then poly(ethylene imine) (PEI) was used to modify the nanopore to change the surface charge in the nanopore and further enhance the interaction between the nanopore and the xylan molecule. It was found that before and after nanopore modification, at negative voltage and low positive voltage, AX didn't generate current blocking signal. On the contrary, BX didn't generate current blocking signal at positive voltage. This phenomenon may be due to the current disturbance driven by electrophoresis and electroosmosis of xylan molecules with weak negative charge. After statistics analysis, the current blocking signal of AX showed that the modified nanopore showed multiple peaks. It indicates that heterogeneous xylan and PEI modified nanopore had stronger interaction. The results show that the nanopore detection technology can show the structural difference of heterogenous branched chain and homogeneous straight chain based on the single characteristic current blocking signal and statistical information, providing a research basis for the structural analysis of water insoluble polysaccharides.

Study on prevention and control measures of sandstone geothermal reinjection plugging.

In the process of geothermal tailwater reinjection of sandstone, the problem of plugging has been seriously restricting the continuous development of geothermal reinjection for many years, and the problems of plugging are complex and changeable. The plugging in the process of reinjection can be divided into physical plugging, chemical plugging, microbial plugging and gas plugging. Given these four types of blocking, according to the mechanism characteristics of the blocking caused by them, this paper puts forward corresponding blocking prevention measures and solves the current blocking problems by filtering, adding a scale inhibitor, intermittent reinjection, adding chlorine dioxide and regular lifting. In addition, the existing reinjection process and the equipment flow are relatively simple and cannot achieve the goal of efficient reinjection. Therefore, a complete set of reinjection processes is designed to ensure the efficient reinjection of sandstone geothermal tailwater.

Unfolding of β-hairpin and α-helical peptides through a biological nanopore.

Nanopore sensing is a useful tool for the rapid detection of analytes at the single-molecule level. Since this technology allows high sensitivity detection based on the ion currents, it is expected to be applied to protein sequencing and folding analysis of proteins. In particular, biological nanopores are 1-4 nm in the size, and proteins pass through the nanopore with unfolding its inside. Therefore, the ion currents will provide insight into the folding process of each secondary structure of proteins, and these analyses may be able to detect specific structures of proteins. Here, we synthesized β-hairpin and α-helix peptides, and analyzed the ion current of the translocation with unfolding. β-hairpin peptides were synthesized using cell-free synthesis, and mass spectrometry characterized each peptide and confirmed secondary structures by fluorescence measurement and circular dichroism spectrum. Channel current measurements identified the behavior of β-hairpin peptides passing through αHL nanopores. As result, signals with three current blocking rates were observed, reflecting the stepwise unfolding of β-hairpin peptides within αHL nanopores. Therefore, we estimated the unfolding behavior of peptides from each blocking state of the ion currents. The estimated results for each level are shown below. Level 1: β-hairpin structure hooked with the upper of nanopore. Level 2: in the pores, the pulling force caused partial unfolding allowing β-hairpin structure to traverse the pore. Level 3: remainder structures unfolded completely and left through the trans entrance. Our experiments with protein denaturants supported our estimations. We are trying to observe the translocation of α-helix peptides, and research the difference in unfolding process of β-hairpin peptides and that of α-helix peptides.

Phosphorous-doped graphene as an efficient interfacial layer material for application in solution-processed photodetectors

This work demonstrates solution-processed photodetectors (PDs) with perovskite as the active layer material, reduced graphene oxide as the hole transport layer and phosphorus-doped graphene (P-G) as the interfacial layer. High detectivity of over 1012 Jones was attained with PDs fabricated with the P-G layer, suggesting the great potential of the P-G layer as an additional dark current blocking layer. Analysis of the diode parameters indicated that this improved optoelectronic performance was attributed to decreased recombination, which resulted from a decrease in interface and trap defects and improved surface morphology, as evident from the field emission scanning electron microscope images. Recombination resistance, carrier lifetime and charge transport resistance were estimated using impedance spectroscopy analysis. It was observed that suppressed recombination due to improved surface morphology, including large grain size, is the main reason for the enhanced optoelectronic performance of PDs fabricated with the P-G layer. This work demonstrates that the use of an additional blocking/interfacial layer can be an effective strategy to improve the performance of solution-processed optoelectronic devices.

Design of the GaN based CAVET with SiO2–InGaN hybrid current blocking layer

The emergence of vertical GaN devices solves the problem of insufficient voltage withstand capacity of horizontal GaN devices. However, the current output capability of vertical GaN devices is not comparable to that of lateral GaN devices. So we propose a Al0.3Ga0.7N/GaN current-aperture vertical electron transistor with a SiO2–In0.05Ga0.95N hybrid current-blocking layer (CBL). Through simulation and in-depth study of the proposed device, the results show that the GaN/InGaN secondary channel enhances the saturation output current of the device, achieving a saturated output current (I DSS) of 985 mA mm−1 and a transconductance (G m) of 256 mS mm−1, which are 30% and 25% higher than that of the single-channel SiO2 CBL device, respectively. The breakdown voltage is 230 V and the on-resistance (R on) is only 0.58 mΩ cm2.

High-power diode lasers with in-situ-structured lateral current blocking for improved threshold, efficiency and brightness

We present high-power GaAs-based broad-area diode lasers with a novel variant of the enhanced self-aligned lateral structure ‘eSAS’, having a strongly reduced lasing threshold and improved peak conversion efficiency and beam quality in comparison to their standard gain-guided counterparts. To realize this new variant (eSAS-V2), a two-step epitaxial growth process involving in situ etching is used to integrate current-blocking layers, optimized for tunnel current suppression, within the p-Al0.8GaAs cladding layer of an extreme-triple-asymmetric epitaxial structure with a thin p-side waveguide. The blocking layers are thus in close proximity to the active zone, resulting in strong suppression of current spreading and lateral carrier accumulation. eSAS-V2 devices with 4 mm resonator length and varying stripe widths are characterized and compared to previous eSAS variant (eSAS-V1) as well as gain-guided reference devices, all having the same dimensions and epitaxial structure. Measurement results show that the new eSAS-V2 variant eliminates an estimated 89% of lateral current spreading, resulting in a strong threshold current reduction of 29% at 90 μm stripe width, while slope and series resistance are broadly unchanged. The novel eSAS-V2 devices also maintain high conversion efficiency up to high continuous-wave optical power, with an exemplary 90 μm device having 51.5% at 20 W. Near-field width is significantly narrowed in both eSAS variants, but eSAS-V2 exhibits a wider far-field angle, consistent with the presence of index guiding. Nonetheless, eSAS-V2 achieves higher beam quality and lateral brightness than gain-guided reference devices, but the index guiding in this realization prevents it from surpassing eSAS-V1. Overall, the different performance benefits of the eSAS approach are clearly demonstrated.

Performance improvement of AlGaInP based red LEDs by combination of omnidirectional mirror and AuZn micro-contacts

An omnidirectional reflector (ODR) consisted of (MgF2)/Ag was employed in AlGaInP-based vertical red light-emitting diodes (LEDs) in order to increase the light extraction hence the wall-plug efficiency. In this structure, the dielectric MgF2 layer with low refractive index acted as current blocking and reflection enhancing layer. The cylindrical AuZn alloy micro-contacts perforated through the MgF2 layer and played roles in current spreading and injection. The area ratio of AuZn micro-contacts was optimized to improve the performance of the LED. The results indicated that increasing the area ratio of micro-contacts led to the improvement of current injection uniformity and reduction of forward voltage especially at higher injection current, but at the expense of light extraction by reducing reflection. After optimized, the best performance of red-light LEDs can be obtained with 3% area ratio of micro-contacts.

A Graph-Based Blocking Approach for Entity Matching Using Contrastively Learned Embeddings

Data integration is considered a crucial task in the entity matching process. In this process, redundant and cunning entries must be identified and eliminated to improve the data quality. To archive this, a comparison between all entities is performed. However, this has quadratic computational complexity. To avoid this, `blocking' limits comparisons to probable matches. This paper presents a k-nearest neighbor graph-based blocking approach utilizing state-of-the-art context-aware sentence embeddings from pre-trained transformers. Our approach maps each database tuple to a node and generates a graph where nodes are connected by edges if they are related. We then invoke unsupervised community detection techniques over this graph and treat blocking as a graph clustering problem. Our work is motivated by the scarcity of training data for entity matching in real-world scenarios and the limited scalability of blocking schemes in the presence of proliferating data. Additionally, we investigate the impact of contrastively trained embeddings on the above system and test its capabilities on four data sets exhibiting more than 6 million comparisons. We show that our block processing times on the target benchmarks vary owing to the efficient data structure of the k-nearest neighbor graph. Our results also show that our method achieves better performance in terms of F1 score when compared to current deep learning-based blocking solutions.