Search

The internal quantum efficiency (IQE) for InGaN/GaN light-emitting diodes (LEDs) grown on [0001] sapphire substrates is strongly affected by various factors including polarization effect in the InGaN/GaN multiple quantum wells (MQWs), insufficient electron and hole injections, low p-type GaN doping efficiency, carrier loss due to the Auger recombination, and current crowding effect especially for the hole current in the p-GaN region. In this work, the remedies taken by the scientific community to enhance the IQE are reviewed, compared and summarized. Meanwhile, this review also discusses alternative ways including polarization self-screening effect, polarization cooling, hole accelerator, and hole modulator. The structural solutions we propose in this work can better improve the device performance without increasing the processing difficulty significantly, and their effectiveness in improving the IQE is further supported by the numerical and experimental studies. For example, on the contrary to common belief, the polarizations in the [0001] oriented InGaN/GaN LEDs can be advantageously used to improve the device performance based on our designs. [ABSTRACT FROM AUTHOR]

The effect of n-AlGaN versus p-AlGaN electron-blocking layers (EBLs) on the performance of InGaN/GaN light-emitting diodes is studied in this work. Experimental results suggest that the n-type EBL leads to higher optical output power and external quantum efficiency, compared to the devices with p-AlGaN EBL, which is commonly used today. Numerical simulations on the carrier distribution and energy band diagram reveal that the n-AlGaN EBL is more efficient in preventing electron overflow, while not blocking the hole injection into the active region, hence leading to higher radiative recombination rate within the multiple quantum wells active region. [ABSTRACT FROM AUTHOR]

We report InGaN/GaN light-emitting diodes (LED) comprising in situ integrated p+-GaN/InGaN/n+-GaN polarization tunnel junctions. Improved current spreading and carrier tunneling probability were obtained in the proposed device architecture, leading to the enhanced optical output power and external quantum efficiency. Compared to the reference InGaN/GaN LEDs using the conventional p+/n+ tunnel junction, these devices having the polarization tunnel junction show a reduced forward bias, which is attributed to the polarization induced electric fields resulting from the in-plane biaxial compressive strain in the thin InGaN layer sandwiched between the p+-GaN and n+-GaN layers. [ABSTRACT FROM AUTHOR]

The internal quantum efficiency (IQE) is one of the key figures of merit for III‐nitride based light‐emitting diodes (LEDs). The Feature Article by Zi‐Hui Zhang et al. (pp. 3078–3102) presents a comprehensive study revealing key factors influencing the IQE for III‐nitride based LEDs. Design strategies were discussed to reduce the electron escape, improve the hole injection, suppress the carrier loss caused by the nonradiative recombination, enhance the current spreading, screen the polarization‐induced electric field in the multiple quantum well (MQW) region, etc. New concepts were introduced and novel device designs were demonstrated to improve the IQE for III‐nitride based LEDs, such as the polarization self‐screening effect, the polarization cooling effect, the hole accelerator, the hole modulator, the PNP‐GaN current spreading layer, etc., enriching device physics for III‐nitride LEDs. These designs also provide general guidelines that might be effective to increase the IQE for III‐nitride deep ultraviolet LEDs, which currently are substantially impacted by the poor carrier injection efficiency, the current crowding effect, the strong quantum confined Stark effect (QCSE) in the MQW region, and so on [ABSTRACT FROM AUTHOR]

An aggregation-induced emission (AIE) strategy is proposed for the kilogram-scale synthesis of full-color solid-state fluorescent (SSF) CDs with quantum yields (QYs) of up to 55.3–27.9% by one-step microwave-assisted pyrolysis of the same precursors. The PL redshift is due to the excessive fluorescence resonance energy transfer induced by the increasing number of aromatic rings on CD surfaces, while the AIE phenomenon is attributed to the suppression of surface carboxyl group motions and the decrease of the non-radiative rate. These CDs show great potential for widespread application in solid-state lighting and displays. [Display omitted] • Solid-state CDs with full-color aggregation-induced emission have been synthesized in a single step for the first time. • These CDs have been obtained on a kilogram scale under normal pressure. • These solid-state CDs exhibit high QYs of 55.3–27.9%. • These CDs show great potential for solid-state lighting and displays. Carbon dots (CDs), one of the most promising luminescent nanomaterials, have attracted widespread concern due to their unique optoelectronic properties and widespread application. However, mass production of solid-state CDs with highly efficient full-color emission has rarely been reported, severely limiting their practical application in solid-state lighting and displays. Here, using an aggregation-induced emission (AIE) strategy, full-color solid-state fluorescent (SSF) CDs with quantum yields (QYs) of up to 55.3–27.9% have been prepared on a kilogram scale through one-step microwave-assisted pyrolysis of the same precursors. Detailed structure–property studies demonstrate that the SSF of CDs is derived from the suppression of surface carboxyl group motions and the decrease of the non-radiative rate in their aggregated state, and that their tunable emission is attributed to the excessive fluorescence resonance energy transfer (FRET) induced by the increasing number of aromatic rings on CD surfaces. Therefore, these CDs exhibit both the AIE enhancement and red shift throughout the entire visible spectrum in the solid state. Finally, because of their excellent AIE properties, these highly efficient SSF CDs have been applied to pattern encryption, large-area luminescent fibrous membranes (LFMs), light-emitting diodes (LEDs), and fingerprint detection. [ABSTRACT FROM AUTHOR]

In this work, unique properties and tremendous advantages for an omni-directional reflector (ODR) on an inclined sidewall for flip-chip AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) are systematically investigated via a three-dimensional finite-difference time-domain method. It is found that although the reflectivity of Ag is far lower than that of Al, the light extraction efficiency for the inclined sidewall DUV LED with the Ag-based ODR is not always lower than that with Al-based one within certain incident angles. The reason is that the total internal reflection (TIR) of the ODR on the inclined sidewall plays an important role in extracting light. We also find that the reflectivity for TIR can be strongly suppressed if surface plasmon polaritons (SPPs) resonance absorption occurs. To avoid SPP resonance absorption, our studies in this work propose the design strategy for ODR on the inclined sidewall as follows: if the ODR structure of the DUV LED with an inclined sidewall adopts thin dielectric layers, the high-index material should be selected as the dielectric layer; if a thick dielectric layer is adopted for the ODR structure, the low-index material should be selected as the dielectric layer. [ABSTRACT FROM AUTHOR]

Paeonol (PAE) is a natural phenolic monomer isolated from the root bark of Paeonia suffruticosa that has been widely used in the clinical treatment of some inflammatory-related diseases and cardiovascular diseases. Much preclinical evidence has demonstrated that PAE not only exhibits a broad spectrum of anticancer effects by inhibiting cell proliferation, invasion and migration and inducing cell apoptosis and cycle arrest through multiple molecular pathways, but also shows excellent performance in improving cancer drug sensitivity, reversing chemoresistance and reducing the toxic side effects of anticancer drugs. However, studies indicate that PAE has the characteristics of poor stability, low bioavailability and short half-life, which makes the effective dose of PAE in many cancers usually high and greatly limits its clinical translation. Fortunately, nanomaterials and derivatives are being developed to ameliorate PAE's shortcomings. This review aims to systematically cover the anticancer advances of PAE in pharmacology, pharmacokinetics, nano delivery systems and derivatives, to provide researchers with the latest and comprehensive information, and to point out the limitations of current studies and areas that need to be strengthened in future studies. We believe this work will be beneficial for further exploration and repurposing of this natural compound as a new clinical anticancer drug. [Display omitted] • Paeonol has a wide range of anticancer pharmacological activities. • Paeonol promotes anticancer effects and reduces side effects of cancer chemotherapy. • Poor stability and pharmacokinetics hinder cancer clinical translation of paeonol. • Nanocarriers improve physicochemical properties and pharmacokinetics of paeonol. • Paeonol derivatives have application potential in cancer therapy. [ABSTRACT FROM AUTHOR]

Here, GaN/AlxGa1-xN heterostructures with a graded AlN composition, completely lacking external p-doping, are designed and grown using metal-organic-chemical-vapour deposition (MOCVD) system to realize three-dimensional hole gas (3DHG). The existence of the 3DHG is confirmed by capacitance-voltage measurements. Based on this design, a p-doping-free InGaN/GaN light-emitting diode (LED) driven by the 3DHG is proposed and grown using MOCVD. The electroluminescence, which is attributed to the radiative recombination of injected electrons and holes in InGaN/GaN quantum wells, is observed from the fabricated p-doping-free devices. These results suggest that the 3DHG can be an alternative hole source for InGaN/GaN LEDs besides common Mg dopants. [ABSTRACT FROM AUTHOR]

Al-rich AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) have a low light extraction efficiency, especially when the emission wavelength is shorter than 280 nm, and this is partially because of the dominant transverse-magnetic polarized light. Our results show that the transverse-electric (TE) polarized light can be obtained even if the emission wavelength becomes even shorter by reducing the quantum well thickness. The ultrathin quantum well enables the enhanced TE-polarized emission that arises from the redistributed subbands for holes. On the contrary to the common belief, we observe a blueshift for the emission wavelength when the AlN composition in the quantum barrier increases. The internal quantum efficiency (IQE) for DUV LEDs with ultrathin quantum wells is no longer determined by the quantum-confined Stark effect, while quantum barrier with high AlN composition is vitally important to improve the electron injection efficiency and thus enhance the IQE. [ABSTRACT FROM AUTHOR]

Methyl-CpG-binding domain proteins (MBPs) connect DNA methylation and histone modification, which are the key changes of somatic cell reprogramming. Methyl-CpG-binding protein 2 (MeCP2) was the first discovered MBP that has been extensively studied in the neurodevelopmental disorder Rett syndrome. However, a role for MeCP2 during cellular reprogramming associated with somatic cell nuclear transfer (SCNT) has not been examined. In this study, we discovered that MeCP2 expression was significantly lower in embryos generated by SCNT compared with those generated by intracytoplasmic sperm injection (ICSI). We genetically modified mouse embryonic fibroblasts (MEFs) to overexpress MeCP2 and serve as donor cells for nuclear transfer (NT) to investigate the effects of MeCP2 on preimplantation development of SCNT embryos. The blastocyst rate (35.71%) of MeCP2 overexpressed embryos (NT+) was significantly greater than in nontransgenic embryos (NT−, 24.29%). Furthermore, immunofluorescence experiments revealed that 5-methylcytosine (5mC) was transferred to 5-hydroxymethylcytosine (5hmC) to a greater extent in NT+ embryos than in NT− embryos. Real-time PCR evaluation of gene expression also showed that embryonic development-associated genes, such as Oct4 and Nanog, were significantly higher in the NT+ group compared to the NT− group. Collectively, these results suggested that MeCP2 facilitated Tet3 activity, enhanced expression of pluripotency-related genes, and eventually improved the development of NT embryos. Finally, we performed chromatin immunoprecipitation to identify direct targets of MeCP2 and constructed a protein interaction network to elucidate several putative MeCP2 targets. [ABSTRACT FROM AUTHOR]

Eleven undescribed isoquinoline alkaloids corybungines A−K including a protoberberine-type alkaloid, an isoquinoline alkaloid with a unique 6-norprotoberberine skeleton, one 13,14-seco-protoberberine-type alkaloid, two 1a,14-seco-protoberberine-type alkaloids with a 4-(hydroxymethyl)phenoxy moiety and six aporphine alkaloids, together with seven known alkaloids, have been isolated from the whole herb extract of Corydalis bungeana Turcz. Their structures and absolute configurations were elucidated based on an analysis of spectroscopic data and electronic circular dichroism (ECD) spectra. (R)-stephanine displayed high antagonistic activity against the dopamine D2 receptor with an IC 50 value of 0.85 ± 0.09 μM in CHO-D2 cells. Additionally, corybungines D, F, H, (R)-roemerine, (R)-vireakine and (R)-tuduranine showed moderate D2 antagonism (IC 50 5.20–26.07 μM). The preliminary structure-activity relationships (SARs) of aporphine alkaloids were discussed. [Display omitted] • Eleven undescribed isoquinoline alkaloids were obtained from Corydalis bungeana. • Spectroscopic data and ECD calculation were used to determine their structures. • Stephanine exhibited high antagonistism on dopamine D2 receptor in CHO-D2 cells. [ABSTRACT FROM AUTHOR]

Four new isoquinoline alkaloids including a benzophenanthridine alkaloid (1), a morphine derivative (2), a narceine-type alkaloid (3) and a simple isoquinoline alkaloid (4), a new amide alkaloid (5) and a new phthalic acid derivative (6), together with eleven known alkaloids (7 – 17) were obtained from the whole herbs extract of Corydalis bungeana Turcz. Their structures and absolute configurations were elucidated by extensive spectroscopic data analysis including HRESIMS, NMR and electronic circular dichroism (ECD) and ECD calculation. Compounds 1 – 17 were evaluated for dopamine D2 receptor activity in CHO-D2 cells. Among them, 16 showed the highest antagonistic activity on the D2 receptor with an IC 50 value of 2.04 ± 0.01 μM. Compounds 14 and 15 exhibited moderate antagonism with IC 50 values of 13.66 ± 2.28 and 31.72 ± 2.52 μM, respectively. [Display omitted] • Five new alkaloids and a new phthalic acid derivative were obtained from Corydalis bungeana. • Their structures were evaluated by the analysis of extensive spectroscopic data. • Compound 16 exhibited significant antagonistic activity on dopamine D2 receptor in CHO-D2 cells. [ABSTRACT FROM AUTHOR]

The external quantum efficiency (EQE) for InGaN/GaN micro-light-emitting diodes ($\mu $ LEDs) is strongly affected by surface recombination at mesa sidewall. In this work, we propose fabricating a Ta2O5 buried insulator in the periphery for the $\mu $ LED mesa to suppress the surface recombination. The Ta2O5 buried insulator with a large relative dielectric constant of 26 can significantly reduce the voltage drop in the insulator so that the lateral energy band below the p-type contact can be bent in the way of generating energy barriers for holes in the mesa edge. This further suppresses the current diffusion to the defected mesa edges for $\mu $ LEDs. Thus, when compared with the reference $\mu $ LED, the proposed $\mu $ LED with $40\times 40\,\,\mu \text{m}^{{2}}$ chip area increases the EQE by 34.6%, and the ON/ OFF current ratio is increased to $10^{{8}}$. A reduced ideality factor of 6.8 is also obtained when compared with other devices. [ABSTRACT FROM AUTHOR]

[Display omitted] Doping Mn2+ into CsPbCl 3 nanocrystals (NCs) yields strong orange emission, while the related emission in Mn2+ doped CsPbBr 3 NCs is impaired seriously. This is mainly ascribed to back energy transfer from the Mn2+ dopant to the host. Doping Mn2+ into perovskites with multiple-quantum-well (MQW) structures may address this issue, where the energy funnels ensure a rapid energy transfer process, and thus resulting in a high photoluminescence quantum yield (PLQY). Here, we have developed an Ag+ assisted Mn2+ doping method in which Mn2+ can be easily doped into Br-based MQW perovskites. In this MQW perovskites, both nanoplatelets (NPLs) and NCs were formed simultaneously, where efficient energy transfer occurred from the NPLs with a higher energy bandgap to the NCs with a smaller energy bandgap, and then to the Mn2+ dopants. White lighting solution with a PLQY up to 98% has been acquired by altering the experimental parameters, such as reaction time and the Pb-to-Mn feed ratio. The successful doping of Mn2+ into CsPbBr 3 host has great significance and shows promising application for next-generation white lighting. [ABSTRACT FROM AUTHOR]

GaN-based ultraviolet (UV) detectors have a considerable application potential in many fields. In this Letter, we report an alternative strategy to realize a high-optical-gain bipolar UV phototransistor based solely on a GaN p-i-n epilayer. The device consists of two tightly adjacent vertical p-i-n structures with a common n-type layer as a floating base. The collector and emitter electrodes are deposited on the two p-type mesas, forming a three-dimensional metal–semiconductor–metal (MSM) like photodetector. As a result, a peak responsivity of 11.7 A/W at a wavelength of 358 nm at 5 V is realized, corresponding to an optical gain of 40 with the assumption of 100% internal quantum efficiency. Different from traditional GaN-based n-p-i-n phototransistors, the optical gain of this detector originates from the accumulated electrons in the n-type floating base upon illumination, which can lower the barrier height between the base and emitter, leading to hole emission from the emitter. Although the structure of this phototransistor is similar to a planar back-to-back Schottky-type MSM photodetector, the response speed is much faster because the gain mainly results from carrier emission rather than MS interface defects. [ABSTRACT FROM AUTHOR]

GaN-based micro-size light-emitting diode (μLED) have emerged as a promising light sources for a wide range of applications in displays, visible light communication etc. In parallel with the two key technological bottlenecks: full-color scheme and mass transfer technique that need overcoming, it is known that the low external quantum efficiency (EQE) is also another challenge for μLEDs from the perspective of manufacturing technology and device physics. The low EQE for GaN based μLEDs is opposite to the common belief for GaN-based LEDs, such that GaN based LEDs are featured with high quantum efficiency, mechanically robust and energy saving. Therefore, in this work, we have reviewed the origin for the low EQE for μLEDs. More importantly, we have also reported the underlying devices physics and proposed optimization strategies to boost the EQE for μLEDs. Our work is targeted to provide a guideline for the community to develop high-performance GaN-based μLEDs. [ABSTRACT FROM AUTHOR]

In this article, we propose and investigate a GaN-based trench metal–insulator–semiconductor barrier Schottky rectifier with a beveled mesa and field plate (BM-TMBS). According to our study, the beveled mesa and field plate structures help to reduce the density of potential lines at the mesa corner and deplete the drift region in two-dimensional mode, respectively. By doing so, the electric field at the bottom corner of the trenches and Schottky contact/GaN interface can be decreased significantly and the breakdown voltage can also be improved remarkably when compared with the conventional TMBS rectifiers and the planar Schottky barrier diodes. Meanwhile, assisted by the beveled mesa structure, the improved current spreading effect and a better conductivity modulation can be obtained in the forward-conduction state. Our studies also show that the electric field profiles and charge-coupling effect can be influenced by the mesa angle, the insulating layer thickness (Tox), and the trench depth (Dtr). As a result, the optimized BM-TMBS rectifiers can obtain a high BV of ∼2 kV and a current density of ∼3 kA/cm2 at the forward bias of 2 V. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have been extensively studied recently by virtue of their extraordinary luminescence characteristics. However, they still suffer from severe stability issues, and contain a toxic metal lead. Here, single crystals of (PEA)4Cu4I4, a lead-free orange-red-emitting organic–inorganic copper-halide compound with a photoluminescence quantum yield (PLQY) of 68%, were synthesized via a simple solvent vapor diffusion process with commercially-available phenylethylamine (PEA) as a ligand. The crystals show superior stability to perovskites with retaining 60% of their initial photoluminescence (PL) intensity after 60 days in water, which is due to the hydrophobic nature of PEA and the stable Cu–N bonds. Phase transition is found to take place upon lowering the temperature, which causes a redshift of the PL peak. The emission band is identified to be associated with triplet cluster-centered (CC) excited states because of their shortened Cu–Cu distances, excitation-independent PL and long PL lifetime. In addition, micron-sized oleic acid capped (PEA)4Cu4I4 particles were developed by a hot-injection method, and they possess similar stability to that of bulk crystals. A monochrome LED was further fabricated by employing the as-prepared micron-sized particles as phosphors, demonstrating their potential for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Carrier imbalance resulting from stronger electron injection from ZnO into quantum‐dot (QD) emissive layer than hole injection is one critical issue that constrains the performance of QDs‐based light‐emitting diodes (QLEDs). This study reports highly efficient inverted QLEDs enabled by periodic insertion of MoO3 into (4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl) (CBP) hole transport layer (HTL). The periodic ultrathin MoO3/CBP‐stacked HTL results in improved lateral current spreading for the QLEDs, which significantly relieves the crowding of holes and thus enhances hole transport capability across the CBP in QLEDs. Comprehensive analysis on the photoelectric properties of devices shows that the optimal thickness for MoO3 interlayer inserted in CBP is only ≈1 nm. The resulting devices with periodic two insertion layers of MoO3 into CBP exhibit better performance compared with the CBP‐only ones, such that the peak current efficiency is 88.7 cd A−1 corresponding to the external quantum efficiency of 20.6%. Furthermore, the resulting QLEDs show an operational lifetime almost 2.5 times longer compared to CBP‐only devices. [ABSTRACT FROM AUTHOR]

The rhizome of Polygonatum sibiricum, known as huang-jing (黄精 in Chinese) in traditional Chinese medicine, is consumed to treat various diseases. During surveys in 2017, diseases reducing the productivity and longevity of the herb seedlings were observed on Mount Maoshan, China, including leaf blight caused by Diaporthe spp. This study aimed to identify the fungal species and evaluate the effectiveness of fungicides (prochloraz, tebuconazole, pyraclostrobin, and zhongshengmycin) against the pathogen in vitro. Based on morphological characteristics, pathogenicity tests, and phylogenetic analysis of the combined genes including the internal transcribed spacer (ITS)1-5.8S rRNA-ITS2 (rDNA-ITS), β-tubulin (TUB), translation elongation factor 1-α (EF1-α), and calmodulin (CAL) gene regions, the causal agent of the new disease was identified as Diaporthe eres. Among the tested fungicides, prochloraz, tebuconazole, and pyraclostrobin significantly inhibited the mycelial growth of D. eres on potato dextrose agar, whereas zhongshengmycin was less effective in inhibiting mycelial growth. The leaf blight caused by D. eres represents a potential threat to P. sibiricum nursery productivity and longevity in China, and its management should be further investigated in the field. [ABSTRACT FROM AUTHOR]

GaN‐based quasi‐vertical PIN diodes are grown on insulating sapphire substrates, and thus both the n‐electrode and the p‐electrode are made on the same side, which causes lateral current injection scheme. Therefore, one of the challenges for this design lies in the serious current crowding at the mesa edges, which leads to the local hole accumulation, and thus the Auger recombination significantly gives rise to the poor conductivity modulation in the drift region when the devices are forwardly biased. Herein, utilizing an embedded PN–GaN junction is proposed, such that the embedded PN–GaN junction is reversely biased when the PIN diode is in the on‐state condition. The built‐in electric field in the reversely biased PN–GaN junction depletes holes at the mesa edges, and correspondingly the Auger recombination can be decreased. The results also show that the proposed structures do not affect the breakdown voltage for PIN diodes. [ABSTRACT FROM AUTHOR]

In this work, and experimentally propose inserting an SiO2 intermediate layer between the Ti and n-AlGaN layer to improve the electron injection efficiency. When the SiO2 intermediate layer is adopted, the SiO2 layer can share a part of the applied voltage and then weakens the surface depletion effect, which is confirmed by the capacitance–voltage measurement. Furthermore, the energy bending of the SiO2 layer pushes the affinity of Ti to be even higher than the conduction band of the Al0.60Ga0.40N layer, which then screens the Schottky barrier and favors the election injection. The influence of the thickness of the SiO2 intermediate layer is also investigated in this work. When the SiO2 layer becomes thick, the tunneling capability of the electrons will be significantly limited due to the increased tunnel region width, leading to increased forward voltage. [ABSTRACT FROM AUTHOR]

Two innovative collectors, i.e. ionic collectors and microemulsion collector were prepared from waste oil to achieve clean flotation of fine coal by gradient flotation, which helps to reduce dependence on traditional nonrenewable collectors. Ionic collectors were prepared and used for the removal of gangue particles from fine coal. Further, the biodiesel prepared from waste oil was emulsified to improve the dispersibility, and microemulsion collector was used for deep purification of fine coal. The effect of microemulsion collector dosage on flotation kinetics was also analyzed. The flotation results show that the ionic collector can effectively remove the gangue particles. When the ionic collector dosage is 1500 g/t, the ash removal reaches 43.63% with 9.17% combustible loss. Zeta analysis shows that the negative electricity on the particle surface hindered the adsorption of gangue particles and collectors in the neutral environment. The flotation kinetics test results of microemulsion collector show that the flotation rate of particles increases with the increase of collector dosage. The first-order model adopted in this study has good fitting accuracy. This study provides an environmentally friendly flotation process for fine coal and realizes the utilization of waste oil. [ABSTRACT FROM AUTHOR]

GaN-based vertical cavity surface emitting laser (VCSEL) features the quasi-vertical architecture, and thus a poor lateral current can be encountered, which can significantly reduce the net modal gain and decrease the lasing power. To prevent the holes from lateral leaking outside of the aperture region, we propose GaN based VCSELs with an NP-GaN structure below the buried insulator layer. The reverse biased NP-GaN junction can produce energy barrier that can better suppress the lateral hole leakage outside of the aperture, therefore the better stimulated radiative rate and device lasing power are obtained. Moreover, we also conduct parametric study regarding the impact of different NP-GaN junction designs with various doping concentrations and architectural sizes for the p-GaN layer on the lateral hole confinement capability. [ABSTRACT FROM AUTHOR]

In this work, we simply take advantage of the polarization effect to efficiently improve the hole injection from the p-type electron blocking layer (p-EBL) to the end of the active region for AlGaN based deep ultraviolet light emitting diodes (DUV LEDs). By properly increasing the AlN composition of AlGaN quantum barriers, a smaller positive polarized charge density at the last quantum barrier/p-EBL interface can be obtained, which correspondingly leads to the suppressed hole depletion and the reduced hole blocking effect in the p-EBL. Meanwhile, we properly increase the quantum well thickness so that the polarized electric field can even more accelerate the holes, and this will homogenize the hole distribution more across the MQWs. Therefore, the external quantum efficiency for DUV LEDs can be enhanced. [ABSTRACT FROM AUTHOR]

In this article, we have systematically investigated the impact of different structural parameters on the breakdown voltage for GaN-based trench MIS barrier-controlled Schottky (TMBS) rectifier. Compared with the planar Schottky rectifier, the TMBS rectifier has field plates on the mesa sidewalls so that the drift region can be depleted in a 2-D manner, which helps to decrease the electric field at the metal/mesa interface. However, the adoption of mesas can make the electric potential lines at the mesa corner dense and has large curvatures. Therefore, the premature breakdown can occur when the electric field therein reaches the critical condition. We find that the electric field profiles can be affected by insulation layer thickness, mesa width, trench depth, and different types of insulation layers. Then, we increase the breakdown voltage by homogenizing the electric field distribution in the mesa region, e.g., the electric field at mesa corners can be decreased by adopting properly thick sidewall insulator and small trench depth. Meanwhile, TMBS rectifier using sidewall insulating material with a large dielectric constant more favors a large breakdown voltage. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted much attention and rely on mixing several colors of perovskites. However, this inevitably leads to a non-uniform light distribution and serious light loss. Here, a novel strategy was demonstrated to obtain white emission by combining the orange and blue emission from CsPb/Mn(Cl/Br)3 QDs. Notably, highly efficient white emission with a photoluminescence quantum yield of 94% was achieved by an anion exchange surface engineering (AESE) strategy. After AESE treatment the surface traps can be eliminated, resulting in improved exciton and Mn2+ emission. A prototype WLED device was fabricated and exhibited excellent optical stability, demonstrating great potential for perovskite QDs in the field of optoelectronics. [ABSTRACT FROM AUTHOR]

The tunable wavelength and high photoluminescence quantum yield of metal halide perovskite quantum dots (QDs) make them an extraordinary material for white light-emitting diodes (WLEDs). However, when perovskites with different halides are mixed, anion exchange occurs between them, limiting the development of WLEDs based on the perovskite. Meanwhile, the red emitting perovskite containing iodine is not stable, which is also a problem to overcome. In this paper, only bromide perovskites were adopted to fabricate the WLED. Hence, the anion exchange reaction can be avoided during their mixing process. CsPbBr3 nanoplatelets, CsPbBr3 QDs, and Mn-doped PEA2PbBr4 nanosheets were used as the blue, green, and red components of the WLEDs, respectively. All these perovskites preserve high luminance and stability, especially the red emitting component. Thus, the WLED shows high efficiency and excellent stability. By adjusting the amounts of these perovskites, WLEDs with different color temperatures were achieved, and the color rendering index reached up to 94. [ABSTRACT FROM AUTHOR]

In this work, we investigate the impact of Si doped AlGaN quantum barriers on the optical powers for [0001] oriented III‐nitride based deep‐ultraviolet light‐emitting diodes (DUV LEDs). The polarization‐induced electric field in the active region is screened as the result of Si‐doped quantum barriers, which gives rise to the improved spatial overlap between electron and hole wave functions. The polarization screening effect within the quantum wells is further proven by the observation of the blue shift for the wavelength. However, the hole distribution across the active region can be significantly retarded if the Si dosage in the quantum barriers is too high. Therefore, the improved radiative recombination within the active region can be realized provided that the Si dosage in the quantum barriers is moderately adjusted to guarantee both the better hole injection efficiency and the screened polarization effect in the multiple quantum wells. [ABSTRACT FROM AUTHOR]

This work proposes the [0001] oriented AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED) possessing a specifically designed p-electron blocking layer (p-EBL) to achieve the high internal quantum efficiency. Both electrons and holes can be efficiently injected into the active region by adopting the Al 0.60 Ga 0.40 N/Al 0.50 Ga 0.50 N/Al 0.60 Ga 0.40 N structured p-EBL, in which a p-Al 0.50 Ga 0.50 N layer is embedded into the p-EBL. Moreover, the impact of different thicknesses for the p-Al 0.50 Ga 0.50 N insertion layer on the hole and electron injections has also been investigated. Compared with the DUV LED with the bulk p-Al 0.60 Ga 0.40 N as the EBL, the proposed LED architectures improve the light output power if the thickness of the p-Al 0.50 Ga 0.50 N insertion layer is properly designed. [ABSTRACT FROM AUTHOR]

We demonstrate an applicable 3D nanohole array comprising pore shape with circular upper opening and sexfoil-shaped bottom, which is obtained by designing the appropriate ratio of the illumination wavelength and the diameter of colloidal nanosphere in combination with the proper photoresist thickness during the photolithography process. A photoresist film with the 3D nanoholes is employed as a physical mask to etch sapphire substrates. LEDs grown on the nanopatterned sapphire substrates deliver 44.3% enhancement in light output power compared to that of LEDs grown on flat sapphire substrates. [ABSTRACT FROM AUTHOR]

In this report, a parametric investigation on the n+-GaN/AlGaN/p+-GaN tunnel junction is made for III-nitride based ultraviolet light emitting diodes (UV LEDs). It is found that, on one hand, by using various Al compositions and AlGaN layer thicknesses, the n+-GaN/AlGaN/p+-GaN tunnel junction can modify the electric field therein, which will affect the carrier tunneling probability and the current-voltage characteristics. On the other hand, the Al composition and the AlGaN layer thickness also have a strong impact on the tunnel region width, which will affect the current flowing path and then influence the hole distribution apart from the p-type ohmic contact. This work conducts a comprehensive analysis and presents an in-depth understanding regarding the n+-GaN/AlGaN/p+-GaN tunnel junction, so that the hole concentration and the internal quantum efficiency can be significantly improved for III-nitride UV LEDs. [ABSTRACT FROM AUTHOR]

Due to the low hole mobility and the unsatisfying p-type doping efficiency, the p-type layer has a low effective hole concentration and a large electrical resistivity that result in poor hole injection efficiency and significant current crowding effect for III-nitride light-emitting diodes (LEDs). In this work, we report a III-nitride LED architecture comprising a dielectric-constant-controlled tunnel junction to improve both the current spreading effect and the hole injection efficiency. The dielectric-constant-controlled tunnel junction is an n+-GaN/AlGaN/p+-GaN heterojunction, in which the dielectric constant for the AlGaN layer is smaller than that for the GaN layer, and therefore, compared to the conventional n+-GaN/p+-GaN homojunction, the electric field within the tunnel junction is increased and hence, the hole injection can be substantially enhanced if the n+-GaN/AlGaN/p+-GaN heterojunction is properly designed. Furthermore, the proposed device can better spread the current compared to the LED without a tunnel junction. As a result, the internal quantum efficiency has been improved for the LED possessing the dielectric-constant-controlled tunnel junction. [ABSTRACT FROM AUTHOR]

Summary: Histone acetylation plays critical roles in chromatin remodeling, DNA repair, and epigenetic regulation of gene expression, but the underlying mechanisms are unclear. Proteasomes usually catalyze ATP- and polyubiquitin-dependent proteolysis. Here, we show that the proteasomes containing the activator PA200 catalyze the polyubiquitin-independent degradation of histones. Most proteasomes in mammalian testes (“spermatoproteasomes”) contain a spermatid/sperm-specific α subunit α4 s/PSMA8 and/or the catalytic β subunits of immunoproteasomes in addition to PA200. Deletion of PA200 in mice abolishes acetylation-dependent degradation of somatic core histones during DNA double-strand breaks and delays core histone disappearance in elongated spermatids. Purified PA200 greatly promotes ATP-independent proteasomal degradation of the acetylated core histones, but not polyubiquitinated proteins. Furthermore, acetylation on histones is required for their binding to the bromodomain-like regions in PA200 and its yeast ortholog, Blm10. Thus, PA200/Blm10 specifically targets the core histones for acetylation-mediated degradation by proteasomes, providing mechanisms by which acetylation regulates histone degradation, DNA repair, and spermatogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • An Ag+-assisted slow-release strategy is proposed to decrease the reaction rate of CsPbBr 3 nanomaterials. • The crystal defects and surface traps are eliminated by excess Ag+ and Br- ions. • Pure blue-emitting nanoplatelets (NPLs) with photoluminescence (PL) quantum yield of 98% are achieved. • The NPL solution has excellent stability, which maintains its PL for over 1.5 years. Compared to the classical II-VI quantum dots (QDs), the reaction kinetics of cesium lead halide perovskite nanocrystals (NCs) are not clear yet because of the fast reaction rate. Here, an Ag+-assisted slow-release strategy is proposed to synthesize CsPbBr 3 nanomaterials, where the reaction rate is decreased and the reaction time is prolonged to days. It is found that the Ag+ ions can bind with the PbBr 2 precursor, which makes the formation of PbBr 6 4- as the rate-limiting step. Shape conversion from dots to nanowires and then to platelets has been observed for the CsPbBr 3. Pure blue-emitting nanoplatelets (NPLs) with near unity photoluminescence quantum yield (QY) are acquired. In addition, the blue-emitting CsPbBr 3 solution is very stable, which has been stored for over 1.5 years without performance degradation. A liquid light-emitting diode (LED) prototype is further fabricated and exhibits excellent stability towards driving currents. [ABSTRACT FROM AUTHOR]

A GaN-based vertical cavity surface emitting laser (VCSEL) featuring a buried ring-shape p-Al 0.10 Ga 0.90 N inside n-GaN contact layer for lateral electron confinement is proposed. The p-AlGaN layer inserted in n-GaN forms an n-p-n structure, acting as a potential barrier to prevent vertical electron migration outside the aperture of the VCSEL, where optical gain is accumulated. By adjusting the thickness and position of the p-AlGaN layer, electron concentration and stimulated recombination rate in the aperture of the VCSEL increased significantly. Consequently, the output power of VCSEL with buried p-AlGaN layer increases by 57% compared to the conventional VCSEL at an injection current of 10 mA. The detailed mechanism responsible for this enhancement is further explored. This work suggests that the introduction of the buried p-AlGaN layer in VCSEL can provide new line of thought in achieving effective current confinement in the development of high-efficient, low-threshold solid-state lasers. • A buried ring-shape p-AlGaN layer is introduced in VCSEL to , confine electrons. • By numerical calculation, total current density in the aperture of VCSEL is significantly increased. • The output power increases by 57.0% for VCSEL with buried p-AlGaN compared to conventional VCSEL. • The effects of thickness and position of buried p-AlGaN on the performance of VCSEL were theoretically investigated. [ABSTRACT FROM AUTHOR]

In this work, we propose to insert an In 0.07 Ga 0.93 N layer into the GaN quantum barriers for InGaN/GaN green light-emitting diodes (LEDs) to achieve the enhanced hole injection and improve the internal quantum efficiency (IQE). Nevertheless, we also find that the insertion layer cannot be too thin, and a properly thick insertion layer is recommended, because the polarization induced electric field in the GaN/In 0.07 Ga 0.93 N/GaN quantum barriers can accelerate holes, and thereby the hole blocking effect at the GaN/In 0.07 Ga 0.93 N interfaces and the increase for the valence band barrier height of p-EBL will be less significant. Other advantage is that the insertion In 0.07 Ga 0.93 N layer can also reduce the polarization induced electric field in the quantum wells, which is helpful to increase the radiative recombination rate. • GaN-InGaN-GaN barriers can improve hole injection by accelerating holes. • GaN-InGaN-GaN barriers can suppress QCSE. • GaN-InGaN-GaN barriers can improve the IQE of InGaN/GaN green light-emitting diodes. [ABSTRACT FROM AUTHOR]

In this work, we propose using metal-insulator-semiconductor (MIS) structure on the n-AlGaN layer to reduce the contact resistance and improve the wall-plug efficiency (WPE) for AlGaN based deep ultraviolet light-emitting diodes (DUV LEDs). The thin insulator between the cathode metal and the n-AlGaN layer can share the bias, which makes the n-AlGaN layer surface less depleted and thus the MIS-type cathode structure favors the intraband tunneling effect for electrons. Moreover, the adoption of the MIS-structure aligns the electron affinity for the metal above the conduction band for the n-AlGaN layer, and this avoids the electron transport by thermionic emission. Thanks to the MIS-type cathode, we find that excellent electron transport can be obtained even if the metal with big electron affinity is used. This work also conducts an in-depth investigation into the impact of the relative dielectric constant, the bandgap, the affinity, the length and the thickness for the insulator on the electron transport and the WPE of DUV LEDs. We find that an insulator with a small dielectric constant is required for promoting the electron tunneling in the MIS-type cathode region. • MIS structure can align the metal affinity above the conduction band of n-AlGaN layer. • Insulator can share the bias and then shrink the width of depletion region. • MIS structure can reduce the dependence of contact resistance on the metal affinity. [ABSTRACT FROM AUTHOR]

This study proposes to increase the breakdown voltage for GaN‐based PIN diodes using the polarization effect, such that a thin AlGaN layer is inserted into the drift layer to modulate the electric field profiles, and by properly designing the device architecture, the electric field in the drift layer can be remarkably reduced by the polarization effect, and this enables the enhancement of the breakdown voltage. The study further investigates the parametric sensitivity of the breakdown voltage for the proposed GaN‐based PIN diodes to different device structures with various drift layer thicknesses. Moreover, it is found that the position of the inserted AlGaN thin layer is also important in affecting the breakdown voltage, such that the AlGaN insertion layer reduces the electric field with the maximum intensity in the drift layer. [ABSTRACT FROM AUTHOR]

In this work, a parametric study revealing the impact of metal‐insulator‐semiconductor (MIS) structure in improving the electron injection between the n‐AlGaN layer and the electrode metal is conducted. After inserting an insulator at the surface between the n‐AlGaN layer and the electrode metal, the energy band bending of the thin insulator manipulates the conduction band barrier height between the electrode and the n‐AlGaN layer, which enables the electrons to more efficiently tunnel through the thin insulator barrier. As a result, the electrical characteristics for the devices are significantly improved if the MIS structure is optimized. Furthermore, the impact of the affinity, the relative dielectric constant, and the bandgap for the insulator on the electron injection is investigated. Meanwhile, it is found that the electron injection is sensitive to the thickness and the length for the insulator. Detailed analysis regarding the electron transport and the device physics are reported in this work. This paper studies the impact of metal‐insulator‐semiconductor (MIS) structure to reduce the contact resistance between the n‐AlGaN layer and the electrode metal. This work reveals the effect of the bandgap, the affinity, the relative dielectric constant, the length, and the thickness of the insulator for the MIS structure, which establishes the guidelines for the community to select the proper insulator. [ABSTRACT FROM AUTHOR]

AlGaN‐based deep ultraviolet light‐emitting diodes (DUV LEDs) are featured with small size, DC driving, no environmental contamination etc., and they are now emerging as the excellent solid‐state light source to replace the conventional mercury based light tubes. Nevertheless, the DUV LEDs are currently affected by the poor external quantum efficiency (EQE), which is caused by the low internal quantum efficiency (IQE) and the very unsatisfying light extraction efficiency (LEE). In this work, the authors disclose the underlying mechanism for the low EQE and summarize the technologies that have been adopted so far for enhancing the EQE. This paper comprehensively reviews III–V nitride based deep ultraviolet light‐emitting diodes (DUV LEDs), which are suffering from the low external quantum efficiency (EQE). This article conducts an in‐depth investigation on the issues that DUV LEDs are encountering now. The strategies that are taken by the research community to improve the EQE are summarized and analyzed. [ABSTRACT FROM AUTHOR]