基于双蓝光有源区激发YAG:Ce荧光粉的高显色性白光LED

在(0001)蓝宝石衬底上利用金属有机化学气相沉积系统,分别生长含有p-AlGaN电子阻挡层和反对称n-AlGaN层的双蓝光波长发射的InGaN/GaN混合多量子阱发光二极管(LED)。结果发现,与传统的具有p-AlGaN电子阻挡层的双蓝光波长LED相比,这种n-AlGaN层能有效改善电子和空穴在混合多量子阱活性层中的分布均匀性和减少电子溢出,并减弱双蓝光发射光谱对电流的依赖性。此外,基于这种双蓝光波长发射的芯片与YAG:Ce荧光粉封装成白光LED能实现高显色性的白光发射,在20 mA电流驱动下,6500 K色温时显色指数达到91,而基于单蓝光芯片的白光LED显色指数只有75。     

离子刻蚀Ⅲ-Ⅴ族半导体材料的损伤机理

采用感应耦合等离子体（ICP）刻蚀技术对InGaN／AlGaN、InAsP／InP应变多量子阱和InAsP／InGaAsP应变单量子阱进行了系统研究，光致发光特性分析表明轻度离子刻蚀后量子阱发光强度得到显著增强，导致发光效率增强的物理机理是：干法刻蚀一方面使量子阱表面变粗糙，使出射光逃逸几率增大；另一方面Ar离子隧穿引起的量子阱内部微结构变化则是发光效率提高的主要原因。     

用于可见光通信的GaN基LED研究进展

发光二极管(LED)的频率响应特性以及在大电流下的发光特性是其在可见光通信中应用的关键性能指标。对于GaN基的LED,减小InGaN/GaN多量子阱中的内建电场,增大空穴的注入,能有效提高大电流下的内量子效率,减弱在大电流情况下出现的效率下降。通过降低与结电容效应相关的RC时间常数以及载流子自发辐射复合寿命,可改善LED的频率响应特性,进一步提高LED的调制带宽。     

高分辨率X射线衍射研究InGaN/GaN多量子阱结构In组分及厚度

应用高分辨X射线衍射技术研究了MOCVD在宝石衬底上生长的InGaN/GaN多量子阱结构.测量(105)非对称面的倒易空间图获得量子阱结构的应变状态.由(002)面三轴衍射0级卫星峰峰位结合应变状况计算获得InGaN层中In含量,从(002)面的ω/2θ衍射谱以及小角反射谱获得多量子阱的一个周期的厚度,GaN层和InGaN层的厚度比.最后通过X射线动力学拟合的方法从(002)面的ω/2θ三轴衍射谱获得In的精确含量是25.5%,InGaN势阱层的精确厚度是1.67nm,GaN阻挡层的精确厚度是22.80nm.     

用InGaN蓝光LED与YAG荧光粉制造自然白光LED

报导了用国内自行研制的InGaN/GaN蓝光发光二极管（LED）与钇铝石榴石（YAG）荧光粉结合而得的白光发光二极管（W－LED），在室温，正向电压3．5V，正向电流20mA时，W－LED轴向亮度为1cd,CIE色坐标为（0．31，0．38），接近纯白色（0．33，0．33）。     

硅衬底InGaN多量子阱材料生长及LED研制

利用低压金属有机化学气相沉积(MOCVD)系统在Si(111)衬底上生长了InGaN多量子阱IED外延片。为克服GaN与Si衬底之间巨大的晶格失配与热失配，引入了AIN低温缓冲层及富镓的GaN高温缓冲层，在Si(111)衬底上获得了无龟裂的InGaN多量子阱LED外延材料。在两英寸外延片内LED管芯的工作电压在3．7～4．1V之间，电致发光波长在465～480nm之间，87％的LED管芯的反向漏电流不大于0．1μA，输出光强为18～30mcd。     

室温准连续多量子阱二极管激光器调谐特性

为了将应变补偿多量子阱（SC-MQW）激光器用于调谐激光吸收光谱（TDLAS）技术进行气体分子检测,研究了SC-MQW激光器在室温、准连续工作模式下的调谐特性.从半导体激光器的速率方程出发,分析了SC-MQW激光器输出波长与温度和注入电流的关系;使用傅里叶变换红外光谱仪（FT-IR）测量了激光器分别在不同电流、温度条件下的调谐特性,得到SC-MQW激光器在允许工作电流范围内的调谐范围接近20nm,电流调谐率约为0.03nm/mA;温度调谐率约为0.25nm/℃;电流和温度联合调谐的波长覆盖范围达50nm.结果表明,该激光器在带状吸收谱的挥发性有机物气体检测方面有很好的应用前景.     

GaN基发光二极管研究进展

GaN基发光二极管(LED)作为目前固态照明和显示等应用中最核心的器件,在完全发挥材料性能的道路上还存在着一些困难.针对蓝光LED内量子效率低和白光LED应用中缺乏简易制备方法的现状,本研究组做出了有意义的富有创新性的工作:提出的宽窄耦合量子阱结构的LED使得蓝光LED的内量子效率得到了很大的提高;通过生长一个用于调节量子阱中的应变和局域化的InGaN插入层,制备出了同一发光层出射白光的单芯片白光LED.     

单量子阱激光器的结构设计与分析

考虑限制层内的载流子，对两种激射波长相同的匹配单量子阱激光器的载流子溢出和增益特性进行了分析。限制层在提供光学限制的同时，对载流子（主要是导带电子）分布也有影响，阱宽一定时，对光学限制层厚工；而随着限制层厚度的增加，注入到量子阱内的载流子比例减小，小阱宽的量子阱虽然光学限制因子和载流子注入比例都较小，但由于其价带耦合小于宽量子阱，从而具有高的模式增益，说明最子阱的能带结构对其光学特性有决定性的作用     

一种具有GaInAsN/GaAs量子阱结构的三结太阳能电池的设计

该文使用传输矩阵法分析了GaInAsN/GaAs量子阱对电子的透射情况,并使用crosslight软件对GaInAsN/GaAs量子阱太阳能电池的伏安特性进行了数值模拟和分析。初步讨论了量子阱的阱宽和垒厚的变化对量子阱电池伏安特性的影响.模拟结果发现垒厚32nm、阱宽7nm的量子阱光伏性能表现良好。作为有源区,当将该量子阱加入到GaAs子电池中,InGaP/GaAs/Ge三结电池在AM0下的短路电流密度达到19.81mA/cm2,比未使用量子阱有源区的三结电池提高了20%。     

Examination of the structural and optical failure of ultra-bright LEDs under varying degrees of electrical stress using synchrotron X-ray topography and optical emission spectroscopy

Failure analysis of ultra-bright LED arrays under varying degrees of electrical stress was performed. Green (565 nm), red (660 nm) and infrared (890 nm) LEDs were subjected to currents between 0 and 1 A and voltages between 0 and 7 V. Using white beam synchrotron X-ray topography (SXRT) in back reflection large-area and section modes, the failure modes of the devices were observed. As the power to each device was increased, a reduction in the definition of device lattice structure due to increased thermal stressing was observed. An increase in strain is witnessed in the devices as they are stressed to the point of near failure. It was noted that at or near failure, the strain fields in the ball-bonded regions of the device become anomalously large (0.08% for the red LED, 0.19% for the green LED and 0.27% for the infrared LED), as observed via orientational contrast on the topographs. This is most likely due to thermally induced damage. The onset of failure took place when the power supplied to each individual LED exceeded 600 mW in the case of the green LEDs, 500 mW for the red LEDs and 745 mW for the infrared LEDs. Surprisingly, this is approximately 25 times greater than the nominal recommended supply for each LED array. This was confirmed by studying the I –V characteristics of the devices in conjunction with their emission spectra. As the power supplied to the devices was increased a narrowing of the radiative bandgap was witnessed in the red and green LEDs; whereas a broadening occurred in the infrared LED. When complete failure occurred in the samples, it was observed that large lattice deformations of the original device structure took place. Optical micrographs indicated that the structure of the devices remains spatially unaltered although the gold bond wire became detached. This confirmed that the distortion observed in the X-ray topographs is mainly due to severe thermally induced lattice distortion. The induced lattice distortion is greatest for the red LEDs; the sample appears to possess distinct and completely misorientated sub-grains.     

Highly Efficient Spectrally Stable Red Perovskite Light‐Emitting Diodes

Perovskite light‐emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi‐2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light‐emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi‐2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi‐2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi‐2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m^?2 and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs.     

Optical properties of Ba2SiO4:Eu phosphor for green light-emitting diode (LED)

Eu²⁺ activated Ba₂SiO₄ phosphors were synthesized at 1573 K by solid-state reactions under a weak reductive atmosphere and systematically investigated by photoluminescence excitation and emission spectra, diffuse reflectance spectra, concentration quenching process and lifetime. The intensive green LEDs were fabricated by combining the synthesized phosphors with near-ultraviolet InGaN chips (λ_em = 395 nm). The Commission Internationale de I’Eclairage color coordinate of the fabricated LEDs is calculated to be x = 0.1904, y = 0.4751 under 20 mA forward-bias current. The dependence of the green LEDs on forward-bias currents shows that as the current increases, the relative intensity simultaneously increases and the color coordinate presents excellent stability, falling in the standard area of the Institute of Transportation Engineers for traffic lights and the Society of Automotive Engineers for automotive displays. These results indicate that the fabricated phosphor-converted green LEDs show great potential for traffic lights and automotive display applications.     

Chromogenic sensing of biogenic amines using a chameleon probe and the red-green-blue readout of digital camera images

We report on sensing spots containing an amine reactive chromogenic probe and a green fluorescent (amine insensitive) reference dye incorporated in a hydrogel matrix on a solid support. Such spots enable rapid and direct determination of primary amines and, especially, biogenic amines (BA). A distinct color change from blue to red occurs on dipping the test spots into a pH 9.0 sample containing primary amines. BAs can be determined in the concentration range from 0.01 to 10 mM within 15 min, enabling rapid, qualitative, and semiquantitative evaluation. In the “photographic” approach, the typically 4-7.5-fold increase in fluorescence intensity of the probe at 620 nm along with the constant green fluorescence at 515 nm of a reference dye are used for quantitation of BAs. The sensing spots are photoexcited with high-power 505 nm light-emitting diodes (LEDs) in a black box. A digital picture is acquired with a commercially available digital camera, and the color information is extracted via red-green-blue (RGB) readout. The ratio of the intensities of the red (signal) channel and the green (reference) channel yields pseudocolor pictures and calibration plots.     

Light‐Emitting Diodes with Cu‐Doped Colloidal Quantum Wells: From Ultrapure Green,Tunable Dual‐Emission to White Light

Copper‐doped colloidal quantum wells (Cu‐CQWs) are considered a new class of optoelectronic materials. To date, the electroluminescence (EL) property of Cu‐CQWs has not been revealed. Additionally, it is desirable to achieve ultrapure green, tunable dual‐emission and white light to satisfy the various requirement of display and lighting applications. Herein, light‐emitting diodes (LEDs) based on colloidal Cu‐CQWs are demonstrated. For the 0% Cu‐doped concentration, the LED exhibits Commission Internationale de L'Eclairage 1931 coordinates of (0.103, 0.797) with a narrow EL full‐wavelength at half‐maximum of 12 nm. For the 0.5% Cu‐doped concentration, a dual‐emission LED is realized. Remarkably, the dual emission can be tuned by manipulating the device engineering. Furthermore, at a high doping concentration of 2.4%, a white LED based on CQWs is developed. With the management of doping concentrations, the color tuning (green, dual‐emission to white) is shown. The findings not only show that LEDs with CQWs can exhibit polychromatic emission but also unlock a new direction to develop LEDs by exploiting 2D impurity‐doped CQWs that can be further extended to the application of other impurities (e.g., Mn, Ag).     

High-efficiency InGaN/GaN/AlGaN light-emitting diodes with short-period InGaN/GaN superlattice for 530–560 nm range

A new method of forming the active region in high-efficiency InGaN/GaN/AlGaN light-emitting diode (LED) structure for long-wave green range is described. The introduction of a short-period InGaN/GaN superlattice situated immediately under the emitting quantum well and overgrown with GaN layer at reduced temperature leads to a more than tenfold increase in the efficiency of emission. For the proposed LEDs, the maximum quantum efficiency was 12% at 552 nm and 8% at 560 nm.     

Fabrication of a nano-cone array on a p-GaN surface for enhanced light extraction efficiency from GaN-based tunable wavelength LEDs

We report on the fabrication of a nano-cone structured p-GaN surface for enhanced light extraction from tunable wavelength light emitting diodes (LEDs). Prior to p-contact metallization, self-assembled colloidal particles are deposited and used as a mask for plasma etching to create nano-cone structures on the p-GaN layer of LEDs. A well-defined periodic nano-cone array, with an average cone diameter of 300?nm and height of 150?nm, is generated on the p-GaN surface. The photoluminescence emission intensity recorded from the regions with the nano-cone array is increased by two times as compared to LEDs without surface patterning. The light output power from the LEDs with surface nano-cones shows significantly higher electroluminescence intensity at an injection current of 70?mA. This is due to the internal multiple scattering of light from the nano-cone sidewalls. Furthermore, we have shown that with an incorporation of InGaN nanostructures in the quantum well, the wavelength of these surface-patterned LEDs can be tuned from 517 to 488?nm with an increase in the injection current. This methodology may serve as a practical approach to increase the light extraction efficiency from wavelength tunable LEDs.     

Improving radiative recombination efficiency of green light-emitting diodes

Although the solid-state lighting industry has achieved huge successes in both red and blue part of the visible spectrum during the last 40 years, light-emitting diodes (LEDs) that emit green light consistently exhibit inferior efficiencies. Thanks to the use of down-conversion phosphors, white LEDs have been commercialised without using green LEDs. However, the efficiency problem of green LEDs still hinders many potential applications of solid-state lighting and limits the overall system efficiency. This review first attempts to conclude and comment on the complex factors that limit the performance of green LEDs with recent research progresses. Then the article focuses on reviewing various strategies to improve green light LED radiative recombination efficiencies.

This review was chosen as a runner up of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining, run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

InGaN-based nano-pillar light emitting diodes fabricated by self-assembled ITO nano-dots

InGaN/GaN based nano-pillar light emitting diodes (LEDs) with a diameter of 200-300 nm and a height of 500 nm are fabricated by inductively coupled plasma etching using self-assembled ITO nano-dots as etching mask, which were produced by wet etching of the as-deposited ITO films. The peak PL intensity of the nano-pillar LEDs was significantly higher than that of the as-grown planar LEDs, which can be attributed to the improvement of external quantum efficiency of the nano-pillar LEDs due to the large sidewall of the nano-pillars. We have also demonstrated electrical pumping of the InGaN/GaN based nano-pillar LEDs with a self-aligned TiO2 layer as a passivation of sidewall of the nano-pillars.     

Thermally stable, dye-bridged nanohybrid-based white light-emitting diodes

Thermally stable red and green light-emitting nanohybrids are introduced as an organic luminescent converter with broad color tunability and a high color rendering index for white light-emitting diodes (LEDs). Nanohybrid-based white LEDs are thermally stable and the color coordination is not changed by heat exposure.