Performance improvement of AlGaN-based deep ultraviolet light-emitting diodes with double electron blocking layers

The AlGaN-based deep ultraviolet light-emitting diodes（LED） with double electron blocking layers（d-EBLs） on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency（IQE）. The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells（QWs） enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.

Efficiency enhancement of ultraviolet light-emitting diodes with segmentally graded p-type AlGaN layer

AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.

Realization of high-efficiency AlGaN deep ultraviolet light-emitting diodes with polarization-induced doping of the p-AlGaN hole injection layer

We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.

Enhanced performance of AlGaN-based ultraviolet light-emitting diodes with linearly graded AlGaN inserting layer in electron blocking layer

The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.

The Transport Mechanisms of Reverse Leakage Current in Ultraviolet Light-Emitting Diodes

The transport mechanisms of the reverse leakage current in the UV light-emitting diodes （380nm） are investi- gated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole-Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05eV, 0.09eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.

Pterygium associated with light-emitting diode use:a case report

Background:Pterygium is a sun-related ocular surface disease secondary to ultraviolet(UV)radiation exposure.Outdoor occupational UV exposure is known to occur secondary to sun exposure.We present a unique case of pterygium associated with indoor occupational light-emitting diode(LED)exposure not previously described in the literature.Case Description:A mobile phone repairer presented with blurred vision and a superotemporal pterygium of his dominant left eye associated with a magnifying glass LED work lamp was diagnosed.This was excised routinely with conjunctival autografting to the defect.Histopathology confirmed benign pterygium and recovery was uncomplicated with resolution of blur.Conclusions:The development of pterygium in our patient may have arisen due to the LED lamp’s wavelengths possibly falling within the UV as well as the upper end of the visible light radiation spectrum.Given the increasing reliance on LED light sources in modern life,ocular conditions arising from exposure to these radiation sources may now need to be listed in the differential diagnoses of patients with pterygium.Appropriate UV protection counselling for these types of lights may also now need to be considered.

Overcoming the fundamental light-extraction efficiency limitations of deep ultraviolet light-emitting diodes by utilizing transverse-magnetic-dominant emission

While the demand for deep ultraviolet(DUV)light sources is rapidly growing,the efficiency of current AlGaN-based DUV light-emitting diodes(LEDs)remains very low due to their fundamentally limited light-extraction efficiency(LEE),calling for a novel LEE-enhancing approach to deliver a real breakthrough.Here,we propose sidewall emission-enhanced(SEE)DUV LEDs having multiple light-emitting mesa stripes to utilize inherently strong transverse-magnetic polarized light from the AlGaN active region and three-dimensional reflectors between the stripes.The SEE DUV LEDs show much enhanced light output power with a strongly upward-directed emission due to the exposed sidewall of the active region and Al-coated selective-area-grown n-type GaN micro-reflectors.The devices also show reduced operating voltage due to better n-type ohmic contact formed on the regrown n-GaN stripes when compared with conventional LEDs.Accordingly,the proposed approach simultaneously improves optical and electrical properties.In addition,strategies to further enhance the LEE up to the theoretical optimum value and control emission directionality are discussed.

Prognostics of radiation power degradation lifetime for ultraviolet light-emitting diodes using stochastic data-driven models

With their advantages of high efficiency,long lifetime,compact size and being free of mercury,ultraviolet light-emitting diodes(UV LEDs)are widely applied in disinfection and purification,photolithography,curing and biomedical devices.However,it is challenging to assess the reliability of UV LEDs based on the traditional life test or even the accelerated life test.In this paper,radiation power degradation modeling is proposed to estimate the lifetime of UV LEDs under both constant stress and step stress degradation tests.Stochastic data-driven predic-tions with both Gamma process and Wiener process methods are implemented,and the degradation mechanisms occurring under different aging conditions are also analyzed.The results show that,compared to least squares regression in the IESNA TM-21 industry standard recommended by the Illuminating Engineering Society of North America(IESNA),the proposed stochastic data-driven methods can predict the lifetime with high accuracy and narrow confidence intervals,which confirms that they provide more reliable information than the IESNA TM-21 standard with greater robustness.

Deep ultraviolet light-emitting diodes based on a well-ordered AlGaN nanorod array

The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes(DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs fabricated by the nanosphere lithography and dry-etching technique. Nanorod DUV LED devices with good electrical properties are successfully realized. Compared to planar DUV LEDs, nanorod DUV LEDs present>2.5 times improvement in light output power and external quantum efficiency. The internal quantum efficiency of nanorod LEDs increases by 1.2 times due to the transformation of carriers from the exciton to the free electron–hole, possibly driven by the interface state effect of the nanorod sidewall surface. In addition, the nanorod array significantly facilitates photons escaping from the interior of LEDs along the vertical direction, contributing to improved light extraction efficiency. A three-dimensional finite-different time-domain simulation is performed to analyze further in detail the TE-and TM-polarized photon extraction mechanisms of the nanostructure. Our results demonstrate the nanorod structure is a good candidate for high-efficiency DUV emitters.

Tandem organic light-emitting diodes with buffer-modified C60/ZnPc as charge generation layer

In this paper, a significant enhancement in current efficiency of the green tandem organic light-emitting diodes(TOLEDs) is demonstrated, which is based on a buffer-modified charge generation layer(CGL) of fullerene carbon(C60)/zinc-phthalocyanine(ZnPc). Al and MoO3 were used as the buffer-modified layers on both sides of the bilayer C60/ZnPc, respectively. Experimental results show that the inserted Al and MoO3 layers can effectively increase the electron extraction of the CGL for obtaining the device performance enhancement. Compared with that of the green TOLEDs without buffer-modified layers in CGL(37.3 cd·A-1), the current efficiency of the green TOLEDs is increased to 54.1 cd·A-1. Further study results find that the performance can also be improved by optimizing the thickness of Al in the CGL. The maximum current efficiency and maximum luminance of the green TOLEDs achieve 63.5 cd·A-1 and 17 873 cd·m-2, respectively, when the multilayer structure of the CGL is Al(3 nm)/C60(5 nm)/ZnPc(5 nm)/MoO3(3 nm).

UV-C和LED红光复合处理对西兰花贮藏品质的影响

为探究短波紫外线(ultraviolet-C,UV-C)和发光二极管(light emitting diode,LED)红光复合处理对西兰花贮藏品质的影响,本研究采用3 kJ/m^2的UV-C辐照和50μmol/(m^2·s)的LED红光辐照单独和复合处理采后西兰花,并将处理后的西兰花贮藏于(20±1)℃条件下,观察其外观品质及生理特性的变化。结果表明:与UV-C、日光(LIGHT)和LED红光分别单独处理西兰花相比,UV-C和LED红光复合处理可有效保持西兰花感官品质,抑制质量损失率和丙二醛含量的增加,延缓叶绿素和VC含量下降,提高过氧化物酶、过氧化氢酶、抗坏血酸过氧化物酶活力。综上,UV-C和LED红光复合处理可以有效保持西兰花品质,延长货架期。

Large-scale and high-quality III-nitride membranes through microcavity-assisted crack propagation by engineering tensile-stressed Ni layers

Epitaxially grown III-nitride alloys are tightly bonded materials with mixed covalent-ionic bonds.This tight bonding presents tremendous challenges in developing III-nitride membranes,even though semiconductor membranes can provide numerous advantages by removing thick,inflexible,and costly substrates.Herein,cavities with various sizes were introduced by overgrowing target layers,such as undoped GaN and green LEDs,on nanoporous templates prepared by electrochemical etching of n-type GaN.The large primary interfacial toughness was effectively reduced according to the design of the cavity density,and the overgrown target layers were then conveniently exfoliated by engineering tensile-stressed Ni layers.The resulting III-nitride membranes maintained high crystal quality even after exfoliation due to the use of GaN-based nanoporous templates with the same lattice constant.The microcavity-assisted crack propagation process developed for the current III-nitride membranes forms a universal process for developing various kinds of large-scale and high-quality semiconductor membranes.

紫外敏感硅光伏二极管的正向特性

通过实验发现高阻衬底浅结的紫外敏感硅光伏二极管的正向偏置Ｃ－Ｖ特性和Ｉ－Ｖ特性与一般ＰＮ结二极管的正向特性有明显地不同。文章在理论分析的基础上提出了该器件的一种新的模型—─两个背靠背的二极管和一个电阻的串联，能很好地解释该器件的正反向特性。

短波紫外发光二极管处理对脂环酸芽孢杆菌的灭活效果及作用机制

短波紫外发光二极管(ultraviolet-C light-emitting diode,UVC-LED)处理是一种新型的非热杀菌技术。本实验以果汁中常见的致腐菌脂环酸芽孢杆菌(Alicyclobacillus acidoterrestris)为目标菌,研究UVC-LED对脂环酸芽孢杆菌的杀灭作用,通过测定处理后细菌胞内核酸和蛋白质泄漏量、细胞膜通透性、胞内活性氧(reactive oxygen species,ROS)的累积水平以及胞内蛋白质和DNA的损伤情况,进一步探究UVC-LED对脂环酸芽孢杆菌的杀菌机理。结果表明:增加UVC-LED的照射剂量可增强其对脂环酸芽孢杆菌的杀灭效果,当照射剂量增加至50 mJ/cm2时,生理盐水中存活的细菌数量降低4.6(lg(CFU/mL))。通过对存活曲线的模拟,发现UVC-LED对生理盐水中脂环酸芽孢杆菌的杀灭作用既符合log-linear模型,又符合Weibull模型。处于不同生长时期的细菌对UVC-LED的敏感度不同,其中处于对数期的细菌对UVC-LED更敏感。照射处理导致膜通透性的改变以及内容物的泄漏,说明细胞膜结构遭到一定程度的破坏,但是胞内ROS的累积水平没有显著提高(P>0.05),拉曼光谱分析表明胞内蛋白结构有所改变,经吖啶橙(acridine orange,AO)染色荧光显微镜观察发现照射处理后菌体DNA的结构变化明显。综上,UVC-LED可通过造成DNA损伤、蛋白结构变化和细胞膜透性改变从而杀灭脂环酸芽孢杆菌,根据破坏程度的不同,推测DNA损伤是细胞死亡的主要原因。

紫外发光二极管对食品接触材料的杀菌动力学及影响因素

紫外发光二极管(ultraviolet C light-emitting diodes,UVC-LEDs)是一种新型紫外光源,具有环境友好、效率高、寿命长等优点,在食品工业领域具有广阔的应用潜力。本实验研究了UVC-LEDs对食品接触材料表面食源性致病菌的失活动力学规律及影响因素。结果表明,UVC-LEDs对接种于食品接触材料表面大肠杆菌O157:H7(Escherichia coli O157:H7)的杀灭效果明显优于对单核细胞增生李斯特菌(Listeria monocytogenes)的杀灭效果。当UVC-LEDs处理剂量为800 mJ/cm^(2)时,接种在玻璃片、定向聚丙烯(oriented polypropylene,OPP)薄膜、不锈钢片和牛皮纸表面的L.monocytogenes分别从初始的5.45、5.56、5.11(lg(CFU/cm^(2)))和5.47(lg(CFU/cm^(2)))降低到0.60、0.70、1.04(lg(CFU/cm^(2)))和5.08(lg(CFU/cm^(2)))。UVC-LEDs处理对不同食品接触材料表面E.coli O157:H7的失活效果也得到类似的结果。Weibull模型(R^(2)>0.922)和Biphasic模型(R^(2)>0.960)均能够较好地拟合UVC-LEDs对玻璃片、OPP薄膜、不锈钢片和牛皮纸表面E.coli O157:H7和L.monocytogenes的失活规律。UVC-LEDs对玻璃片、OPP薄膜、不锈钢片和牛皮纸杀菌效果依次降低,这可能与食品接触材料的表面粗糙度和亲水性等性质有关。以上结果表明,UVC-LEDs对食品接触材料的杀菌效果可能受到微生物种类及接触材料表面特性等因素的影响。

短波紫外线结合发光二极管红光辐照对香椿保鲜效果的影响

目的比较短波紫外线(ultraviolet C,UV-C)与发光二极管(light-emitting diode,LED)红光复合辐照和单一LED红光辐照对贮藏期香椿采后保鲜效果的影响。方法将挑选后的香椿分为3组,在4℃下贮藏,通过测定感官指标、失重率、色差值、可溶性固形物含量、维生素C(vitamin C,VC)含量、还原糖含量、菌落总数、丙二醛(malondialdehyde,MDA)含量、1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基清除能力、过氧化物酶(peroxidase,POD)和多酚氧化酶(polyphenol oxidase,PPO)活性指标比较不同处理的差异。结果将红光复合辐照与单一LED红光辐照的处理效果比较后发现:在外观品质方面,前者显著地提高香椿的感官品质,其感官品质评分比对照高9.6分;有效地降低香椿的失重率,其失重率仅为对照的52.5%;在营养品质上,前者可以保持更高的可溶性固形物、VC和还原糖含量,其VC含量是对照的11.1倍;前者不仅有效地抑制香椿叶片中微生物的生长,还显著地减缓MDA含量的积累,其MDA含量只有对照的72.3%;前者还保持更高的DPPH自由基清除能力,也显著地提高POD和PPO的活性,其PPO活性比对照高32.4%。结论UV-C结合LED红光辐照和单一LED红光辐照都有利于保持香椿的贮藏品质,UV-C结合LED红光复合辐照对香椿的保鲜效果更好。

Aggregation-induced narrowband isomeric fluorophores for ultraviolet nondoped OLEDs by engineering multiple nonbonding interactions

Traditional donor-acceptor type organic luminescent materials usually suffer from unfavorable spectral broadening and fluorescence quenching problems arising from strong inter/intra-chromophore interactions in aggregation state.Here,two ultraviolet carbazole-pyrimidine isomers(named o-DCz-Pm and m-DCz-Pm)with novel aggregation-induced narrowband phenomenon are constructed and systematic investigated by experiments and theoretical simulations.Benefitting from strengthened steric hindrance and multiple noncovalent interactions,the nonradiative decay,vibrational motion,and structural relaxation of singlet state can be effectively suppressed in aggregation state.Consequently,the electroluminescence peak of 397 nm,full width at half maximum of 21 nm and external quantum efficiency of 3.4%are achieved simultaneously in nondoped o-DCz-Pm-based device.This work paves an avenue toward the development of high-performance narrowband nondoped ultraviolet materials and organic light-emitting diodes.

Design of LED display based on FPGA

If single chip micro computer controls light-emitting diode(LED),it needs abundant peripheral resources,but in this way,it is not convenient to be expanded,modified and maintained.In order to overcome these shortcomings,field programmable gate array(FPGA)is used to control LED.The hardware design uses low power consumption and high performance device EP1C6Q240C8.Quartus II is the software development environment.There are three modules built under the software development environment:divided clock module,word stock module and LED dot matrix display module,and these independent modules are connected to be a whole system.Finally,32×64 dot matrix display is realized successfully.It is convenient for the customer to adjust the three independent modules according to actual demands and it is easier to realize online updation.

Crafting host materials for narrowband blue OLEDs with low efficiency roll-off by the medium-ring strategy

The pursuit of high-performance narrowband blue organic light-emitting diodes(OLEDs)is of paramount importance in both academic research and industrial applications.While obvious strides have been made in the design of narrowband blue emitters,the development of appropriate host materials has evidently trailed behind.Herein,we introduce a medium-ring strategy for crafting host molecules based on the heptagonal tribenzo[b,d,f]azepine(TBA)unit.The twisted three-dimensional(3D)architecture of the TBA framework not only endows the host molecules with fast hole-transporting pathways but also effectively reduces exciton quenching.Equipped with two TBA units,DTBA,synthesized with ease,demonstrates a huge horizontal orientation factor(Θ//)of 93.5%and a broad emission spectrum for accelerating the energy transfer process in the emitting layer,which contributes to enhancing device performance.We have fabricated high-performance narrowband blue OLEDs using DTBA as the host,FIrpic as the phosphor sensitizer,and the widely used boron-nitrogen-containing multiple resonance emitter BCz-BN.These devices exhibit a maximum external quantum efficiency(EQEmax)as high as 31.0%with an impressively lowefficiency roll-off.Even at a high luminance level of 10,000 cd m^(-2),the EQE value remains noteworthy at 20.3%,marking a significant advancement in BCz-BN-based devices.

紫外发光二极管对P.deceptionensis CM2杀菌作用及机制

研究紫外发光二极管(UVC-LEDs)处理对假单胞菌CM2(P.deceptionensis CM2)的灭活作用及机理。结果表明,UVC-LEDs处理对P.deceptionensis CM2具有良好灭活效果,且灭活效果随处理剂量升高而增强。处理剂量8 mJ/cm^(2)和4000 mJ/cm^(2)时,纯培养体系和鸡肉表面P.deceptionensis CM2分别降低6.09 log10 CFU/mL和2.45log10 CFU/g。场发射扫描电镜(FE-SEM)结果表明,经UVC-LEDs(4000 mJ/cm^(2))处理后,P.deceptionensis CM2细胞形态发生明显皱缩。随着处理剂量(1000~4000 mJ/cm^(2))的增加,P.deceptionensis CM2细胞中碘化丙啶荧光强度显著增强,胞外核酸和蛋白含量显著增加。以上结果表明,UVC-LEDs杀菌作用可能与细胞结构破坏、细胞膜通透性增加有关。试验结果为UVC-LEDs在食品安全控制和保鲜领域的应用提供参考。