InGaN蓝光与CdTe纳米晶基白光LED

报道了倒装焊InGaN蓝光LED与黄光CdTe纳米晶的复合结构。利用蓝光作为CdTe纳米晶的激发源,通过光的下转换机制,将部分蓝光转化为黄光,复合发射出白光。室温下正向驱动电流为10mA时,发光色品坐标为x=0.29,y=0.30。实验表明,该复合结构白光LED的一大优点在于,复合光的色品坐标几乎不随正向驱动电流大小变化,颜色稳定。     

衬底弯曲度对GaN基LED芯片性能的影响

利用低压MOCVD系统在弯曲度值不同的蓝宝石衬底上生长了GaN基LED外延结构并制作芯片。测量了芯片的主要电学和光学参数,并分析了衬底弯曲度值对芯片性能的影响。分析结果表明:存在弯曲度的衬底预先弛豫了外延层中的部分应力,改善了外延层的质量,从而提高了LED芯片的性能。随着衬底弯曲度值的逐渐增加,下层GaN对有源层中InGaN材料的压应力作用不断减小,导致芯片的主波长逐渐发生蓝移。     

Oblique-angle sputtered AlN nanocolumnar layer as a buffer layer in GaN-based LED

This work presents an aluminum nitride (AlN) nanocolumnar layer sputtered at various oblique angles and its application as a buffer layer for GaN-based light-emitting diodes (LEDs) that are fabricated on sapphire substrates. The OA-AlN nanocolumnar layer has a diameter of about 30-60 nm. The GaN-based LED structure is perpendicularly extended from the OA-AlN nanocolumnar layer. Then, the nanocolumnar structure is merged into p-GaN layer to form a mesa structure with a diameter of about 200-600 nm on the surface of the GaN-based LED. Moreover, optical characteristics of the LED were studied using photoluminescence, along with the blue-shifts observed as well.     

Improved light extraction of GaN-based light-emitting diodes with surface-textured indium tin oxide electrodes by nickel nanoparticle mask dry-etching

GaN-based light-emitting diodes (LEDs) with surface-textured indium tin oxide (ITO) as a transparent current spreading layer were fabricated.The ITO surface was textured by inductively coupled plasma (ICP) etching technology using a monolayer of nickel (Ni) nanoparticles as the etching mask.The luminance intensity of ITO surface-textured GaN-based LEDs was enhanced by about 34% compared to that of conventional LED without textured ITO layer.In addition,the fabricated ITO surface-textured GaN-based LEDs would present a quite good performance in electrical characteristics.The results indicate that the scattering of photons emitted in the active layer was greatly enhanced via the textured ITO surface,and the ITO surface-textured technique could have a potential application in improving photoelectric characteristics for manufacturing GaN-based LEDs of higher brightness.     

The influence of ZnO seed layers on n-ZnO nanostructure/p-GaN LEDs

Light-emitting diodes (LEDs) were formed by hydrothermally growing n-ZnO nanostructures on p-GaN with or without seed layers. The performance of the fabricated LEDs was studied. The seed layers not only have a great influence on the morphology and density of the ZnO nanostructures but also determine the lighting bias and emitting mechanism. The LEDs without seed layers and with sputtered seed layers exhibit light emission only under reverse bias, which is believed due to the GaN buffer layer/p-GaN p–n junction. The LEDs with sol–gel seed layers exhibit light emission under both forward and reverse biases. With the increase of the forward bias, the LEDs first demonstrate a red electroluminescence emission coming from the sol–gel seed layers and then demonstrate an orange emission coming from the ZnO nanorods. The sol–gel seed layer and the interface play a very important role in the electroluminescence.     

GaN-based LEDs for light communication

Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm² by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ～7900 A/cm², a maximum modulation bandwidth of ～227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles. Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.     

Enhancing light extraction of GaN-based blue light-emitting diodes by a tuned nanopillar array

Surface patterning of p-GaN to improve the light extraction efficiency of GaN-based blue light-emitting diodes(LEDs) has been investigated. Periodic nanopillar arrays on p-GaN have been fabricated by polystyrene(PS) nanosphere lithography; the diameter of the nanopillars can be tuned to optimize the electrical and optical properties of the LEDs. The electroluminescence intensity of the nanopillar-patterned LEDs is better than that of conventional LEDs; the greatest enhancement increased the intensity by a factor of 1.41 at a 20 mA injection current. The enhancements can be explained by a model of bilayer film on a GaN substrate. This method may serve as a practical approach to improve the efficiency of light extraction from LEDs.     

Improved light extraction of GaN-based light-emitting diodes with surface-patterned ITO

The surface patterning of the indium tin oxide (ITO) transparent current layer has been investigated to improve the light extraction efficiency of GaN-based light-emitting diodes (LEDs). LEDs with periodic micro-hexagon patterned ITO have been fabricated utilizing standard lithography techniques and inductively coupled plasma (ICP) technology. The luminance intensity of the LED chips with patterned ITO following 160 s ICP etching was enhanced by about 50% compared to the LED chips with unpatterned ITO. Detailed processing parameters are provided. scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to examine the micro-structures. The results indicate that the surface-patterned ITO technique could have potential applications in high-power GaN-based LEDs.     

Status of GaN-based green light-emitting diodes

GaN-based blue light emitting diodes(LEDs) have undergone great development in recent years,but the improvement of green LEDs is still in progress.Currently,the external quantum efficiency(EQE) of GaN-based green LEDs is typically30%,which is much lower than that of top-level blue LEDs.The current challenge with regard to GaN-based green LEDs is to grow a high quality In GaN quantum well(QW) with low strain.Many techniques of improving efficiency are discussed,such as inserting Al GaN between the QW and the barrier,employing prestrained layers beneath the QW and growing semipolar QW.The recent progress of GaN-based green LEDs on Si substrate is also reported:high efficiency,high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2,and the relevant techniques are detailed.     

表面InGaN厚度对GaN基发光二极管特性的影响

通过调整GaN基发光二极管(LED)表面InGaN层的厚度,发现在20 mA电流驱动下,LED器件的正向压降有明显差距.本文考虑了极化效应的影响,通过求解InGaN/GaN三角形势阱内二维空穴气浓度以及空穴隧穿概率的变化,求得了表面InGaN层厚度不同时器件正向压降的变化趋势,发现理论结果与实验结果有很好的吻合.同时得到了获得最低正向压降的表面InGaN厚度. 关键词： 极化 二维空穴气 隧穿概率     

表面InGaN厚度对GaN基发光二极管特性的影响

通过调整GaN基发光二极管(LED)表面InGaN层的厚度，发现在20 mA电流驱动下，LED器件的正向压降有明显差距.本文考虑了极化效应的影响，通过求解InGaN/GaN三角形势阱内二维空穴气浓度以及空穴隧穿概率的变化，求得了表面InGaN层厚度不同时器件正向压降的变化趋势，发现理论结果与实验结果有很好的吻合.同时得到了获得最低正向压降的表面InGaN厚度.     

High-brightness gallium nitride nanowire UV–blue light emitting diodes

We report on high-brightness GaN nanowire UV–blue light emitting diodes (LEDs), which are fabricated by coupling of n-GaN nanowires and p-GaN substrates using two assembly methods, random dispersion (RD) and dielectrophoresis assisted assembly deposition (DAAD). These GaN nanowire LEDs have bright UV–blue emission (411–437?nm) from the n-GaN nanowire/p-GaN substrate junction and the light emission is strong enough to be observed with the naked eye even for a single GaN nanowire LED. The results reported here should have significant implications for the fabrication of highly efficient, low-cost UV–blue LEDs with low power consumption, as compared to conventional thin-film based GaN LEDs.     

全息技术制作二维光子晶体蓝宝石衬底提高发光二极管外量子效率

为了提高GaN基发光二极管(LED)的外量子效率,在蓝宝石衬底制作了二维光子晶体.衬底上的二维光子晶体结构采用激光全息技术和感应耦合等离子体(ICP)干法刻蚀技术制作,然后采用金属氧化物化学气相沉积(MOCVD)技术在图形蓝宝石衬底(PSS)上生长2μm厚的n型GaN层,4层量子阱和200nm厚的p型GaN层,形成LED结构.衬底上制作的二维光子晶体为六角晶格结构,晶格常数为3.8μm,刻蚀深度为800nm.LED器件光强输出测试结果显示,在PSS上制作的LED(PSS-LED)的发光强度普遍高于蓝宝石平 关键词： 全息 发光二极管 图形蓝宝石衬底 外量子效率     

Study on GaN-based light emitting diode with InGaN/GaN/InGaN multi-layer barrier

The current study investigates GaN-based light-emitting diodes (LEDs) with InGaN/GaN/InGaN multi-layer barrier (MLB). Simulation results show that GaN-based LEDs with MLB have better performance than conventional GaN-based LEDs with only one GaN barrier because of the enhancement in hole injection into the quantum well and decrease in electron leakage current.     

Enhancement of LED light extraction via diffraction of hexagonal lattice fabricated in ITO layer with holographic lithography and wet etching

A novel method for enhancing light extraction efficiency of LEDs via diffraction of the lattice fabricated in ITO layers of LEDs is proposed. The lattice fabrication process includes holographic lithography and wet etching. 3-beam interference holographic approach was used to fabricate large-area hexagonal lattice mask which can cover 2-inch semiconductor wafer, and acid etching was used to transfer the lattice structure into p-contact ITO layer. 1.4 fold enhancement of light output at 20 mA injection current was obtained from GaN-based LEDs in the primary experiment. The lattice fabrication process is rapid and cost-effective thus enabling industrial mass production of high brightness LEDs.     

Progress in research of GaN-based LEDs fabricated on SiC substrate

The influence of buffer layer growth conditions on the crystal quality and residual stress of GaN film grown on silicon carbide substrate is investigated.It is found that the Al GaN nucleation layer with high growth temperature can efficiently decrease the dislocation density and stress of the GaN film compared with Al N buffer layer.To increase the light extraction efficiency of GaN-based LEDs on Si C substrate,flip-chip structure and thin film flip-chip structure were designed and optimized.The fabricated blue LED had a maximum wall-plug efficiency of 72% at 80 m A.At 350 m A,the output power,the Vf,the dominant wavelength,and the wall-plug efficiency of the blue LED were 644 m W,2.95 V,460 nm,and 63%,respectively.     

磁控反应溅射AlN缓冲层对GaN基LED器件性能的影响

以直流磁控反应溅射法(RMS)在图形化蓝宝石衬底上制备的AlN薄膜作为缓冲层,采用金属有机化学气相沉积法(MOCVD)外延生长了GaN基LED。与MOCVD生长的低温GaN缓冲层相比,RMS制备的AlN缓冲层具有表面更平整、颗粒更小的形核岛,有利于促进GaN外延的横向生长,减少了形核岛合并时的界面数量和高度差异,降低了缺陷和位错产生的几率。研究结果表明,溅射AlN缓冲层取代传统低温GaN缓冲层后,外延生长的GaN材料具有更高的晶体质量,LED器件在亮度、漏电和抗静电能力等光电特性上均有明显提升。     

Enhancement of the light extraction of GaN-based green light emitting diodes via nanohybrid structures

Improvement in the light extraction efficiency (LEE) of GaN-based green light emitting diodes (LEDs) with ZnO nanostructures synthesized by a hydrothermal method is reported. Formation of ZnO nanorods, hemispheres, and cones was controlled by varying the pH of the aqueous synthesis solution. The shape of the ZnO nanostructures integrated onto the LEDs shows a strong relationship with the LEE characteristics of GaN-based green LEDs. The electroluminescence (EL) intensity of LEDs covered by ZnO nanostructures increased compared to conventional LEDs. In terms of LEE, LEDs with surface-textured ZnO hemispheres showed the highest EL intensity, which can be attributed to an increase in the effective critical angle, the escape cone, and multiple scattering. Finite difference time domain (FDTD) simulation was conducted to theoretically confirm the experimental results.     

Improvement of GaN light-emitting diodes with surface-treated Al-doped ZnO transparent Ohmic contacts by holographic photonic crystal

This letter presents a holographic photonic crystal (H-PhC) Al-doped ZnO (AZO) transparent Ohmic contact layer on p-GaN to increase the light output of GaN-based LEDs without destroying the p-GaN. The operating voltage of the PhC LEDs at 20 mA was almost the same as that of the typical planar AZO LEDs. While the resultant PhC LED devices exhibited significant improvements in light extraction, up to 1.22 times that of planar AZO LEDs without PhC integration. Temperature dependence of the integrated photoluminescence intensity indicates that this improvement can be attributed to the increased extraction efficiency due to the surface modification. These results demonstrate that the surface-treated AZO layer by H-PhCs is suitable for fabricating high-brightness GaN-based LEDs.     

激光剥离技术实现垂直结构GaN基LED

为改善GaN基发光二极管(Light-emitting diode,LED)的电学特性和提高其输出光功率,采用激光剥离技术,在KrF准分子激光器脉冲激光能量密度为400mJ/cm2的条件下,将GaN基LED从蓝宝石衬底剥离,结合金属熔融键合技术,在300℃中将GaN基LED转移至高电导率和高热导率的硅衬底,制备出了具有垂直结构的GaN基LED,并对其电学和光学特性进行了测试。结果表明:在110mA注入电流下,垂直结构器件的开启电压由普通结构的3.68V降低到了3.27V;在560mA注入电流下,器件输出光功率没有出现饱和现象;采用高电导率和高热导率的硅衬底能有效地改善GaN基LED的电学和光学特性。