Optimization of AlGaN-based deep ultraviolet light emitting diodes with superlattice step doped electron blocking layers.

The superlattice electron blocking layer (EBL) has been proposed to reduce the electron leakage of the deep ultraviolet light emitting diodes (DUV-LEDs). However, the hole transport is hindered by the barriers of EBL and the improvement of hole injection efficiency still suffers enormous challenges. The superlattice step doped (SLSD) EBL is proposed to improve the hole injection efficiency while enhancing the electron confinement capability. The SLSD EBL enhances the electron confinement capability by multi-reflection effects on the electron wave function. And a built-in electric field towards the active region is generated by superlattice step doping, which facilitates the transport of holes into the multiple quantum wells. The Advaced Physical Model of Semiconductor Devices (APSYS) software is used to simulate the DUV-LEDs with conventional EBL, superlattice EBL, superlattice doped EBL, and SLSD EBL. The results indicate that the SLSD EBL contributes to the increased electron concentration in the multiple quantum wells, the reduced electron leakage in the p-type region, the increased hole injection current, and the increased radiative recombination rate. When the current is 60 mA, the external quantum efficiency of DUV-LED with SLSD EBL is increased to 5.27% and the output power is increased to 13.81 mW. The SLSD EBL provides a valuable reference for solving the problems of serious electron leakage and insufficient hole injection of the DUV-LEDs.

Study of ultraviolet light emitting diodes with InGaN quantum dots and lattice matched superlattice electron blocking layers.

Ultraviolet light emitting diodes (UV-LEDs) face the challenges including insufficient hole injection and severe electron leakage. Quantum dots (QDs) have been proven to provide three-dimensionally localized states for carriers, thereby enhancing carrier confinement. Therefore, UV-LEDs employing InGaN QDs are designed and studied in this paper. The APSYs software is used to simulate UV-LEDs. Simulation results indicate that the QDs effectively improve the electron and hole concentration in the active region. However, UV-LEDs with QDs experience efficiency droop due to serious electron leakage. What's more, the lattice mismatch between last quantum barrier (LQB) and electron blocking layer (EBL) leads to the polarization field, which induces the downward band bending at the LQB/EBL interface and reduces effective barrier height of EBL for electrons. The AlInGaN/AlInGaN lattice matched superlattice (LMSL) EBL is designed to suppress electron leakage while mitigating lattice mismatch between LQB and EBL. The results indicate that the utilization of QDs and LMSL EBL contributes to increasing the electron and hole concentration in the active region, reducing electron leakage, enhancing radiative recombination rate, and reducing turn-on voltage. The efficiency droop caused by electron leakage is mitigated. When the injection current is 120 mA, the external quantum efficiency is increased to 9.3% and the output power is increased to 38.3 mW. This paper provides a valuable reference for addressing the challenges of insufficient hole injection and severe electron leakage.

Non-heavy doped pnp-AlGaN tunnel junction for an efficient deep-ultraviolet light emitting diode with low conduction voltage.

While traditional tunnel junction (TJ) light-emitting diodes (LEDs) can enhance current diffusion and increase hole injection efficiency, their reliance on highly doped AlGaN layers to improve hole tunneling efficiency results in a higher conduction voltage, adversely impacting LED device performance. This paper proposes a non-heavy doped pnp-AlGaN TJ deep ultraviolet (DUV) LED with a low conduction voltage. By inserting the TJ near the active region, between the electron blocking layer and the hole supply layer, the need for heavily doped AlGaN is circumvented. Furthermore, the LED leverages the polarization charge in the pnp-AlGaN TJ layer to decrease the electric field strength, enhancing hole tunneling effects and reducing conduction voltage. The non-heavy doped pnp-AlGaN TJ LED effectively enhances carrier concentration in the quantum well, achieving a more uniform distribution of electrons and holes, thus improving radiative recombination efficiency. Consequently, at an injection current of 120 A/cm2, compared to the traditional structure LED (without TJ), the proposed LED exhibits a 190.7% increase in optical power, a 142.8% increase in maximum internal quantum efficiency (IQE) to 0.85, and a modest efficiency droop of only 5.8%, with a conduction voltage of just 4.1V. These findings offer valuable insights to address the challenges of high heavy doped TJ and elevated conduction voltage in high-performance TJ DUV LEDs.

Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip.

III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top-down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

Optimization of AlGaN-based deep UV LED performance by p-AlInGaN/AlInGaN graded superlattice electron blocking layer.

In this paper, we significantly improved the internal quantum efficiency and output power of AlGaN-based deep UV (DUV) LEDs by replacing the conventional p-AlGaN electron blocking layer (EBL) with the p-AlInGaN/AlInGaN graded superlattice (SL) EBL. Simulation results show that the introduction of the p-AlInGaN graded SL EBL improved the carrier distribution while having the lower electric field, thus increasing the radiative recombination rate in multiple quantum wells (MQWs). The highest IQE obtained by p-AlInGaN/AlInGaN graded SL EBL is 96.6%, which is 44.9% higher than the conventional p-AlGaN EBL with no efficiency droop. At the same time, the output power is 4.6 times that of the conventional p-AlGaN EBL. It is believed that the proposed p-AlInGaN graded SL EBL will be helpful in the development of high-performance DUV LEDs.

Enhanced performance in deep-ultraviolet laser diodes with an undoped BGaN electron blocking layer.

Aluminum-rich p-AlGaN electron blocking layers (EBLs) are typically used for preventing overflow of electrons from the active region in AlGaN-based deep ultraviolet (DUV) laser diode (LD). However, these cannot effectively prevent electron leakage and form barrier layers, which affects the hole injection efficiency. Herein, the traditional p-AlGaN EBL in LD is replaced with an undoped BGaN EBL. The undoped BGaN EBL LD increases the effective barrier height of the conduction band to prevent the leakage of electrons and decreases the energy loss caused by the polarization induced electric field, enhancing the hole injection. The slope efficiency of the undoped BGaN EBL LD is 289% higher than that of the highly doped AlGaN EBL LD, and its threshold current is 51% lower. Therefore, the findings of this study provide insights for solving the problems of electron leakage and insufficient hole injection in high-performance and undoped EBL DUV LDs.

Prophylactic Use of Antibiotics for Fever After Drainage Removal Following a Dural Tear During Lumbar Spinal Surgery: A Retrospective Study.

BACKGROUND Dural tear and subsequent cerebrospinal fluid leakage are frequent complications during lumbar spine surgery. This retrospective study aimed to investigate the risk factors and the use of prophylactic antibiotics in patients with fever after drainage removal (FDR) following lumbar dural tear during lumbar spinal surgery. MATERIAL AND METHODS The authors retrospectively analyzed 2812 patients who underwent different spinal surgical procedures from January 2015 to December 2017. The basic information of patients was obtained to analyze the risk factors of dural tear and FDR. The patients were divided into 5 groups according to their antibiotic strategies for FDR (no antibiotics, ceftriaxone, vancomycin, ceftriaxone+vancomycin, other antibiotics). Body temperature, laboratory test results, and pathogen profiles were collected for analysis. RESULTS There were 326 cases diagnosed as dural tear, including 198 cases of FDR. Sex, age, type of disease, and previous lumbar surgery played significant roles in the dural tear rate (P<0.05). Patients older than 60 years old had a higher incidence of FDR after dural tear (P<0.05). There was no significant difference in the incidence of surgical site infection among the various treatment groups (P>0.05). CONCLUSIONS Age has obvious effect on dural tear and FDR, whereas sex, revision surgery, primary diagnosis, and procedure type only affect the rate of dural tear. The prophylactic use of antibiotics has no effect on the incidence of surgical site infection when fever after drainage removal occurred in patients with dural tear.

Proposing the n+-AlGaN tunnel junction for an efficient deep-ultraviolet light-emitting diode at 254 nm emission.

Toxic and low-pressure deep-ultraviolet (DUV) mercury lamps have been used widely for applications of surface disinfection and water sterilization. The exposure of pathogens to 254 nm DUV radiations has been proven to be an effective and environmentally safe way to inactivate germs as well as viruses in short time. To replace toxic mercury DUV lamps, an n +-A l G a N tunnel junction (TJ)-based DUV light-emitting diode (LED) at 254 nm emission has been investigated. The studied conventional LED device has maximum internal quantum efficiency (IQE) of 50% with an efficiency droop of 18% at 200A/c m 2. In contrast, the calculated results show that a maximum IQE of 82% with a 3% efficiency droop under a relatively higher injection current was estimated by employing a 5 nm thin n +-A l G a N TJ with a 0.70 aluminum molar fraction. In addition, the TJ LED emitted power has been improved significantly by 2.5 times compared with a conventional LED structure. Such an efficient n +-A l G a N TJ-based DUV LED at 254 nm emission might open a new way, to the best of our knowledge, for the development of safe and efficient germicidal irradiation sources.

Compositionally graded AlGaN hole source layer for deep-ultraviolet nanowire light-emitting diode without electron blocking layer.

The electron blocking layer (EBL) plays a vital role in blocking the electron overflow from an active region in the AlGaN-based deep-ultraviolet light-emitting diode (DUV-LED). Besides the blocking of electron overflow, EBL reduces hole injection toward the active region. In this work, we proposed a DUV nanowire (NW) LED structure without EBL by replacing it with a compositionally continuous graded hole source layer (HSL). Our proposed graded HSL without EBL provides a better electron blocking effect and enhanced hole injection efficiency. As a result, optical power is improved by 48% and series resistance is reduced by 50% with 4.8 V threshold voltage. Moreover, graded HSL without EBL offer reduced electric field within the active region, which leads to a significant increment in radiative recombination rate and enhancement of spontaneous emission by 34% at 254 nm wavelength, as a result, 52% maximum internal quantum efficiency with 24% efficiency drop is reported.

Monolithic III-nitride photonic integration toward multifunctional devices.

The multiple functionalities of III-nitride semiconductors enable the integration with different components into a multicomponent system with enhanced functions. Here, we propose to fabricate and characterize a monolithic InGaN photonic circuit of a transmitter, waveguide, and receiver on an III-nitride-on-silicon platform. Both the transmitter and the receiver, sharing identical InGaN/GaN multiple-quantum-well structures and fabrication procedures, work to emit light and detect light independently. The 8 µm wide and 200 µm long InGaN waveguide couples the modulated light from the transmitter and sends the guided light to the receiver, leading to the formation of an in-plane light transmission system. The induced photocurrent at the receiver is highly sensitive to the light output of the transmitter. Multi-dimensional light transmissions are experimentally demonstrated at 200 Mb/s. These multifunctional photonic circuits open feasible approaches to the development of III-nitride multicomponent systems with integrated functions for comprehensive applications in the visible region.

Progress of Micro-Stimulation Techniques to Alter Pigeons' Motor Behavior: A Review from the Perspectives of the Neural Basis and Neuro-Devices.

Pigeons have natural advantages in robotics research, including a wide range of activities, low energy consumption, good concealment performance, strong long-distance weight bearing and continuous flight ability, excellent navigation, and spatial cognitive ability, etc. They are typical model animals in the field of animal robot research and have important application value. A hot interdisciplinary research topic and the core content of pigeon robot research, altering pigeon motor behavior using brain stimulation involves multiple disciplines including animal ethology, neuroscience, electronic information technology and artificial intelligence technology, etc. In this paper, we review the progress of altering pigeon motor behavior using brain stimulation from the perspectives of the neural basis and neuro-devices. The recent literature on altering pigeon motor behavior using brain stimulation was investigated first. The neural basis, structure and function of a system to alter pigeon motor behavior using brain stimulation are briefly introduced below. Furthermore, a classified review was carried out based on the representative research achievements in this field in recent years. Our summary and discussion of the related research progress cover five aspects including the control targets, control parameters, control environment, control objectives, and control system. Future directions that need to be further studied are discussed, and the development trend in altering pigeon motor behavior using brain stimulation is projected.

Tuning the electronic properties and band offset of h-BN/diamond mixed-dimensional heterostructure by biaxial strain.

The h-BN/diamond mix-dimensional heterostructure has broad application prospects in the fields of optoelectronic devices and power electronic devices. In this paper, the electronic properties and band offsets of hexagonal boron nitride (h-BN)/(H, O, F, OH)-diamond (111) heterostructures were studied by first-principles calculations under biaxial strain. The results show that different terminals could significantly affect the interface binding energy and charge transfer of h-BN/diamond heterostructure. All heterostructures exhibited semiconductor properties. The h-BN/(H, F)-diamond systems were indirect bandgap, while h-BN/(O, OH)-diamond systems were direct bandgap. In addition, the four systems all formed type-II heterostructures, among which h-BN/H-diamond had the largest band offset, indicating that the system was more conducive to the separation of electrons and holes. Under biaxial strain the bandgap values of the h-BN/H-diamond system decreased, and the band type occurred direct-indirect transition. The bandgap of h-BN/(O, F, OH)-diamond system increased linearly in whole range, and the band type only transformed under large strain. On the other hand, biaxial strain could significantly change the band offset of h-BN/diamond heterostructure and promote the application of this heterostructure in different fields. Our work provides theoretical guidance for the regulation of the electrical properties of h-BN/diamond heterostructures by biaxial strain.

Dynamic temporal neural patterns based on multichannel LFPs Identify different brain states during anesthesia in pigeons: comparison of three anesthetics.

Anesthetic-induced brain activity study is crucial in avian cognitive-, consciousness-, and sleep-related research. However, the neurobiological mechanisms underlying the generation of brain rhythms and specific connectivity of birds during anesthesia are poorly understood. Although different kinds of anesthetics can be used to induce an anesthesia state, a comparison study of these drugs focusing on the neural pattern evolution during anesthesia is lacking. Here, we recorded local field potentials (LFPs) using a multi-channel micro-electrode array inserted into the nidopallium caudolateral (NCL) of adult pigeons (Columba livia) anesthetized with chloral hydrate, pelltobarbitalum natricum or urethane. Power spectral density (PSD) and functional connectivity analyses were used to measure the dynamic temporal neural patterns in NCL during anesthesia. Neural decoding analysis was adopted to calculate the probability of the pigeon's brain state and the kind of injected anesthetic. In the NCL during anesthesia, we found elevated power activity and functional connectivity at low-frequency bands and depressed power activity and connectivity at high-frequency bands. Decoding results based on the spectral and functional connectivity features indicated that the pigeon's brain states during anesthesia and the injected anesthetics can be effectively decoded. These findings provide an important foundation for future investigations on how different anesthetics induce the generation of specific neural patterns.

Stability simulation analysis of targeted puncture in L4/5 intervertebral space for PELD surgery.

Introduction: The application prospects of percutaneous endoscopic lumbar discectomy (PELD) as a minimally invasive spinal surgery method in the treatment of lumbar disc herniation are extensive. This study aims to find the optimal entry angle for the trephine at the L4/5 intervertebral space, which causes less lumbar damage and has greater postoperative stability. To achieve this, we conduct a three-dimensional simulated analysis of the degree of damage caused by targeted puncture-based trephine osteotomy on the lumbar spine. Methods: We gathered clinical CT data from patients to construct a lumbar model. This model was used to simulate and analyze the variations in trephine osteotomy volume resulting from targeted punctures at the L4/5 interspace. Furthermore, according to these variations in osteotomy volume, we created Finite Element Analysis (FEA) models specifically for the trephine osteotomy procedure. We then applied mechanical loads to conduct range of motion and von Mises stress analyses on the lumbar motion unit. Results: In percutaneous endoscopic interlaminar discectomy, the smallest osteotomy volume occurred with a 20° entry angle, close to the base of the spinous process. The volume increased at 30° and reached its largest at 40°. In percutaneous transforaminal endoscopic discectomy, the largest osteotomy volume was observed with a 50° entry angle, passing through the facet joints, with smaller volumes at 60° and the smallest at 70°. In FEA, M6 exhibited the most notable biomechanical decline, particularly during posterior extension and right rotation. M2 and M3 showed significant differences primarily in rotation, whereas the differences between M3 and M4 were most evident in posterior extension and right rotation. M5 displayed their highest stress levels primarily in posterior extension, with significant variations observed in right rotation alongside M4. Conclusion: The appropriate selection of entry sites can reduce lumbar damage and increase stability. We suggest employing targeted punctures at a 30° angle for PEID and at a 60° angle for PTED at the L4/5 intervertebral space. Additionally, reducing the degree of facet joint damage is crucial to enhance postoperative stability in lumbar vertebral motion units.

Performance improvement of nitride semiconductor-based deep-ultraviolet laser diodes with superlattice cladding layers.

A deep-ultraviolet (DUV) laser diode (LD) consisting of specifically designed cladding layers involving superlattice nitride alloy has been proposed. Simulation studies of different cladding layers were carried out using Crosslight software. It was found that the proposed structure effectively suppresses the leakage of the optical field from the active region and the optical confinement coefficient is 1.45 times higher than that of the conventional structure. The proposed structure has a significant increase in laser power with a low threshold current. Moreover, the introduction of novel cladding layer suppresses the electron and hole leakage from the multiple quantum well (MQW) region, which provides an attractive solution for increasing the stimulated recombination rate in the MQW region leading to the improvement in the performance of the DUV LD.

Microplastics in soil can increase nutrient uptake by wheat.

Microplastics can perturb microbial nutrient-mining strategies. However, the mechanism by which microplastics affect the resource-acquisition strategies of crops in agricultural systems remains unknown. The nutrient-acquisition potential of crops and microbes was investigated under treatments with two common microplastics (polyethylene [PE] and polyvinyl chloride [PVC]) at 0%, 1%, and 5% (w/w). Different root resource-acquisition strategies disturbed microbial nutrient turnover in the rhizosphere in response to microplastic addition. Specifically, the ß-1,4-glucosidase (BG) hotspot expanded, whereas the rhizosphere expansion of BG activity decreased. A decrease of less than PE1% (w/w) and an expansion of less than PE5% (w/w) in the 1,4-N-acetyl-glucosaminidase (NAG) hotspot with wider rhizosphere expansion of NAG activity indicated that higher doses of PE allow roots to uptake additional N. The phosphomonoesterase (PHOS) hotspot decreased in PE1% (w/w) and expanded in PE5% (w/w), but rhizosphere expansion did not change under PE treatments. However, both NAG and PHOS hotspots expanded with decreasing rhizosphere expansion under PVC treatments, indicating that PVC limits the utilization of available N and P, forcing the crop to obtain nutrients from the narrow root zone. These results indicate that adding PE microplastics increases the demand for and consumption of NH4+-N and NO3--N by wheat.

The first principle calculation of improving p-type characteristics of BxAl1-xN.

AlN is one of the third-generation semiconductor materials with wide application prospects due to its 6.2 eV band gap. In the application of semiconductor deep ultraviolet lasers, progress is slow due to the difficulty in obtaining p-type AlN with good performance. In this paper, the commonly used way of Mg directly as AlN dopant is abandoned, the inhibition effect of the B component on self-compensation of AlN crystal was studied. The improvement of self-compensation performance of AlN crystal by B component is studied by first principles calculation. The results show that the addition of B component can increase the hole concentration of AlN, which is conducive to the formation of p-type AlN.

Epitaxial Combination of Two-Dimensional Hexagonal Boron Nitride with Single-Crystalline Diamond Substrate.

Hexagonal boron nitride (hBN) and diamond are promising materials for next-generation electronics and optoelectronics. However, their combination is rarely reported. In this study, we for the first time demonstrate the success to direct growth of two-dimensional (2D) hBN crystal layers on diamond substrates by metalorganic vapor phase epitaxy. Compared with the disordered growth we found on diamond (100), atomic force microscopy, X-ray diffraction, and transmission electron microscopy results all support 2D hBN with highly oriented lattice formation on diamond (111). Also, the epitaxial relationship between hBN and diamond (111) substrate is revealed to be [0 0 0 1]hBN // [1 1 1]diamond and [1 0 1̅ 0]hBN // [1 1 2̅]diamond. The valence band offset at hBN/diamond (111) heterointerface determined by X-ray photoelectron spectroscopy is 1.4 ± 0.2 eV, thus yielding a conduction band offset of 1.0 ± 0.2 eV and type II staggered band alignment with a bandgap of 5.9 eV assumed for hBN. Furthermore, prior thermal cleaning of diamond in a pure H2 atmosphere smoothens the surface for well-ordered layered hBN epitaxy, while thermal cleaning in a mixed H2 and NH3 atmosphere etches the diamond surface, creating many small faceted pits that destroy the following epitaxy of hBN.

Full-duplex light communication with a monolithic multicomponent system.

A monolithic multicomponent system is proposed and implemented on a III-nitride-on-silicon platform, whereby two multiple-quantum-well diodes (MQW-diodes) are interconnected by a suspended waveguide. Both MQW-diodes have an identical low-In-content InGaN/Al0.10Ga0.90N MQW structure and are produced by the same fabrication process flow. When appropriately biased, both MQW-diodes operate under a simultaneous emission-detection mode and function as a transmitter and a receiver at the same time, forming an in-plane full-duplex light communication system. Real-time full-duplex audio communication is experimentally demonstrated using the monolithic multicomponent system in combination with an external circuit.