具有电流阻挡层的垂直结构氮化镓发光二级管的光电特性研究

本文对具有电流阻挡层（CBL）的氮化镓垂直结构发光二极管（LED）进行了研究。不带有CBL、带有非欧姆接触CBL和带有二氧化硅CBL的垂直LED芯片样品被制作出来,并对它们进行了光电性能的测试。结果表明这种带有非欧姆接触CBL和带有二氧化硅CBL的氮化镓垂直结构LED的光输出效率相比不带有CBL的分别高出40.6%和60.7%。不带有CBL的、带有非欧姆接触CBL和带有二氧化硅CBL的氮化镓垂直结构LED在350毫安下的效率分别下降到各自最高效率的72%、78%和85.5%。另外,带有非欧姆接触CBL的氮化镓垂直结构LED具有更优越的抗静电性能。     

Improved performance of lateral GaN-based light emitting diodes with novel buried CBL structure in ITO film and reflective electrodes

In this letter, lateral GaN-based Light Emitting Diodes (LEDs) with a SiO₂ current blocking layer (CBL) buried in the indium tin oxide (ITO) film and highly reflective metal materials have been proposed. Compared with the conventional CBL structure which was inserted between ITO film and p-type GaN, simulation results showed that LEDs with a buried CBL in the ITO film effectively facilitated current spreading under the CBL. We demonstrated that buried CBL was beneficial for suppressing current crowding (CC) effect around the edge of CBL and may facilitate higher LED efficiency. Furthermore, experimental results showed that LEDs with the buried structure we proposed showed lower working voltage and higher light output power (LOP) compared with those with conventional CBL structure. These results further confirmed that the buried CBL scheme was effective to reduce current crowding (CC) effect. In addition, highly reflective metal materials of Cr/Al/Pt/Au were employed to reduce light absorption and achieve high light extraction efficiency.     

Improvement in the Light Output Power of GaN-Based Light-Emitting Diodes by Natural-Cluster Silicon Dioxide Nanoparticles as the Current-Blocking Layer

In this study, the fabrication and characterization of InGaN–GaN multiple-quantum-well light-emitting diodes (LEDs) with silicon dioxide ($hbox{SiO}_{2}$) nanoparticles as the current-blocking layer (CBL) are described. The performance was improved by introducing $hbox{SiO}_{2}$ nanoparticles, not deposited by commonly used plasma-enhanced chemical vapor deposition, as the CBL beneath the p-pad. The injected current was forced to spread outside instead of flowing directly downward. At 20 mA, the light output power of the LED with a CBL was increased 15.7% as compared to that of the conventional LED. The forward voltage of the LED with the $hbox{SiO}_{2}$ nanoparticle CBL was 3.34 V at 20 mA, which was slightly higher than that of the conventional LED (3.29 V). The increase in the light output power can be attributed to the injection of additional current into the light-emitting active layer of the LED by the $hbox{SiO}_{2}$ nanoparticles CBL and thus a reduction in optical absorption at the p-pad.      

Improving Light Output Power of the GaN-Based Vertical-Injection Light-Emitting Diodes by Mg$^{+}$ Implanted Current Blocking Layer

A method for forming a current blocking layer (CBL) by ion implantation in GaN-based vertical-injection light-emitting diodes (VI-LEDs) was proposed. It was found that the use of CBL in VI-LEDs can effectively reduce the current crowding effect and enhance the light output power. The uniform emission intensity distribution of VI-LEDs with CBL was demonstrated by electroluminescence measurements. Experimental results show that the wall-plug efficiency was enhanced by 12.3% at an injection current of 20 mA, compared to that of VI-LEDs without CBL, and by 56.2% compared to that of conventional LEDs. The device simulation results reveal that the current path can be blocked by CBL, resulting in high light extraction efficiencies and large current densities within the effective emission region of active layers.      

硅光敏三极管光开通现象的研究

本文研究了硅npn型光敏三极管的光开通现象.证实了光开通实质是光触发引起的晶闸管导通现象.查明了其原因是在于底面集电极处形成的非欧姆接触.具体讨论了由于金在底面形成p型层而构成的npnp四层结构的实例.     

Performance of InGaN-GaN LEDs fabricated using glue bonding on 50-mm Si substrate

Vertical InGaN-GaN light-emitting diodes (LEDs) epitaxial films were successfully fabricated on a 50-mm Si substrate using glue bonding and laser liftoff technology. A high-temperature stable organic film, rather than a solder metal, was used as the bonding agent. It was found that the light output of the vertical InGaN LED chip exceeded that of the conventional sapphire-substrate LEDs by about 20% at an injection current of 20 mA. The vertical InGaN LEDs operated at a much higher injection forward current (280 mA) than sapphire-substrate LEDs (180 mA). The radiation pattern of the vertical InGaN LEDs is more symmetrical than that of the sapphire-substrate LEDs. Furthermore, the vertical InGaN LEDs remain highly reliable after 1000 h of testing.     

Effect of the surface texturing shapes fabricated using dry etching on the extraction efficiency of vertical light-emitting diodes

On the surfaces of GaN-based light-emitting diodes (LEDs) having an n-side-up vertical electrode structure formed by the laser lift-off, various shapes of photoresist-patterned surface textures were formed by inductively coupled plasma etching and their effect on the light emission efficiencies was investigated. By the formation of various shapes of surface textures, the light output efficiency was increased from 37% to 45% compared to that without surface textures. The increase of light output efficiency was related to the increase of sidewall scattering, the decrease of reflected loss, and the decrease of cavity wall effect that occurs for the vertical LEDs by the increase of sidewall surface area.     

A simple surface-emitting LED array useful for developingfree-space optical interconnect

A surface-emitting light source array of homojunction visible (660 nm) GaAsP light-emitting diodes (LEDs) has been developed to demonstrate the feasibility of new microimaging techniques in vertical optical interconnects. The fabrication process used to create arrays of these independently addressable light sources is described. A study of contact annealing showed that a two-step furnace anneal yielded higher radiance devices than rapid thermally annealed devices. A 4×4 array was used with a reflective focusing diffractive optic element to image light onto photodetectors, thereby proving the usefulness of this source in developing vertical optical interconnects     

垂直结构GaN基LED的侧壁优化技术

为了提升垂直结构LED提取效率,针对器件侧壁出光的研究越发引起研究人员的关注。由于GaN的高折射率,大部分有源区发出的光线将被限制在GaN层内横向传输。对不同刻蚀倾角侧面的光提取效率进行分析模拟,模拟结果显示,LED的提取效率可以通过侧壁倾斜角度的优化得以提升。实验结果表明,特定侧壁倾角器件的提取效率相比较垂直侧壁提高了18.75%,电致发光光谱测试(EL)结果表明,实验结论与理论计算值基本吻合。本结论对垂直结构GaN基LED器件的优化设计与性能提升有重要指导意义。     

Highly reliable nitride-based LEDs with SPS+ITO upper contacts

Nitride-based blue light emitting diodes (LEDs) with an n/sup +/-short period superlattice (SPS) tunnel contact layer and an indium tin oxide (ITO) transparent contact were fabricated. Compared with conventional nitride-based LEDs with Ni/Au upper contacts, it was found that we could achieve a 60% increase in electroluminescence (EL) intensity by using ITO upper contacts. However, it was also found that the lifetime of ITO LEDs were much shorter. Furthermore, it was found that we could achieve a longer lifetime and a smaller reverse leakage current (I/sub R/) by the deposition of a SiO/sub 2/ layer on top of the ITO LEDs.     

Hybridisation of LEDs with silicon microsensors

This paper presents the experiments we performed for hybrid integration of LEDs with silicon optical readout microsensors. LEDs were face down mounted, in a silicon cavity, on the same wafer with the sensor. The edge-emitted light is coupled into SiON waveguides. The LEDs hybridization steps were included in the technological processes of two types of silicon microsensors: chemo-optical and mechano-optical sensors. The proper technological steps succession was established according to the limitation imposed by lithography on wafers with deep groves and the thermal behavior of transducing layers. The main problem we solved was the matching of all the involved processes: integrated optics, micromachining, thin-film technology, CMOS technology.     

Transfer of GaN-Based Light-Emitting Diodes From Silicon Growth Substrate to Copper

III-nitride light-emitting diodes (LEDs) grown on Si (111) substrates have the potential of low-cost manufacturing for solid-state lighting and display, by taking advantage of the well-developed IC technologies of silicon. In this letter, LEDs grown on silicon substrates were transferred onto copper substrates, to maximize light extraction and heat dissipation. On Si substrates, $hbox{300} times hbox{300} muhbox{m}^{2}$ multiple quantum well InGaN LEDs were first grown and processed. The top surface of the fabricated devices was then temporarily bonded to a sapphire wafer and the Si substrate was chemically etched. Ti/Al/Ti/Au layers were deposited on the backside of LEDs. An 80-$muhbox{m}$ -thick copper layer was electroplated and the temporary bonding was removed, resulting in LEDs on copper substrate. The optical output power of LEDs on copper increased by $sim$ 70% as compared to that of the LEDs on silicon. The improved performance was attributed to the removal of the light-absorbing Si substrate and the good thermal conductivity of copper.      

钝化材料对深紫外LED器件性能的影响

对比研究了SiO2、聚酰亚胺薄膜、SiNx/旋涂玻璃(SOG)复合材料等钝化材料对倒装焊深紫外LED器件抑制漏电流恶化、改善器件可靠性的作用。实际测试结果表明,未钝化和采用SiO2、聚酰亚胺、SiNx/SOG复合钝化膜后,倒装焊紫外LED短路漏电比例分别为100%、100%、55%和18%,采用聚酰亚胺和SiNx/SOG复合钝化膜的器件点亮1 000h后光衰分别为67%和20%。分析表明,SiNx与SOG结合使用有效降低了表面电荷复合几率并改善了倒装焊短路问题;SOG还进一步降低了表面的粗糙度,改善了由于AlGaN外延表面上的深凹槽结构引起的器件漏电及倒装焊金属溢流的短路,从而大大提高了可靠性。     

III-Nitride-Based Light-Emitting Diodes With GaN Micropillars Around Mesa and Patterned Substrate

In this paper, the textured-sidewall mesa and GaN microsize pillars (?-pillars) around the mesa region were fabricated on III-nitride light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS). We demonstrated that the light-waveguide mode outside the mesa region of III-nitride LEDs could be disrupted by a GaN ?-pillar around the mesa region and PSS. We found that the power enhancement of LEDs with textured sidewall, ?-pillars around the mesa, and PSS from ray-tracing simulation was about 65% larger than that of conventional LEDs. It was found that we could achieve a high power enhancement of about 60% of LEDs with textured sidewall, ? -pillars around the mesa, and a patterned substrate, and it was close to the result of simulation. It was also found that the light intensity outside the mesa region with ? -pillars of LEDs with or without a patterned substrate would decay in proportion to the distance away from the mesa edge, by studying the light emission intensity image of the whole LEDs. The decay lengths for the textured sidewall and ?-pillars around the mesa LEDs with or without a patterned substrate are 12 and 17 ?m, respectively. We understand that the light outside the mesa region could be extracted earlier by introducing the GaN ?-pillars and patterned substrate together.     

Si基发光的研究进展

回顾了Si基发光的研究历程,归纳分析了新近几种实现Si发光的方法和其优缺点,其中包括多孔Si发光、GeSi/Si量子阱发光、Sip-n结位错发光、CMOSSi基发光、PERL结构Si基发光等方法。重点介绍了PERL结构Si基发光,分析了结构设计中的几个关键性因素。该结构利用了光电转换可逆性原理,基于普通的单光子和双光子辅助次禁带弱光发射过程,通过把位于有关的次禁带波长的吸收最小化,同时减少二极管内寄生无辐射复合的作用范围。期望通过该综述提高国内研究者对PERLSi基发光的重视,开拓以PERL为新思路、新方法的Si基光互连方向研究的新进展。     

Enhancement of light output power of GaN-based vertical light emitting diodes by optimizing n-GaN thickness

The light output and electrical characteristics of GaN-based vertical light emitting diodes were investigated as a function of n-GaN thickness. The forward voltage increases from 3.34 to 3.42 V at an injection current of 350 mA as the n-GaN thickness decreases from 5.0 to 2.0 μm. Even at a high injection current of 2.0 A, LEDs with 2.0 μm-thick n-GaN reveal stable forward characteristics which are comparable to those of LEDs with 5.0 μm-thick n-GaN. All the samples exhibit almost the same reverse current up to approximately −8 V. The output power increases with decreasing n-GaN layer thickness. For example, LEDs with 2.0 μm-thick n-GaN yield about 12% higher light output power as compared to LEDs with 5.0 μm-thick n-GaN. Their light output power continuously increases without saturation as the injection current increases up to 1 A. The n-GaN thickness dependence of the electrical characteristics is described and discussed.     

Light output enhancement for nitride-based light emitting diodes via imprinting lithography using spin-on glass

The production of micrometric imprinted structures made of spin-on glass (SOG) is demonstrated in this paper. Two different mold materials, sapphire and silicon, are fabricated by dry and wet etching for both 1-D and 2-D patterns. The imprinting pressure, the imprinting temperature, and anti-adhesive films are also discussed. Finally, the imprinted structures are integrated with the chip process of the light emitting diodes (LEDs) in order to understand how the output optical efficiency is affected by those embossed SOG structures. In our study, both the 1-D and 2-D surface structures proved to be useful in enhancing the light extraction efficiency. The output intensity of the 2-D micro-cylinder structure on LEDs increased to 26.2% compared with that of conventional LEDs. In addition, the forward voltage is almost kept identical under a 20 mA injection.     

基于纳米球镜光刻的选区生长的光子晶体提高InGaN LED光提取效率的研究

We report a new method for the fabrication of two-dimensional photonic crystal(PhC) hole arrays to improve the light extraction of GaN-based light-emitting diodes(LEDs).The PhC structures were realized using nanospherical-lens photolithography and the selective-area epitaxy method,which ensured the electrical properties of the LEDs through leaving the p-GaN damage-free.At a current of 350 mA,the light output power of LEDs with PhC hole arrays of 450 nm and 600 nm in diameter with the same lattice period of 900 nm were enhanced by 49.3% and 72.2%,respectively,compared to LEDs without a PhC.Furthermore,the LEDs with PhC hole structures showed an obviously smaller divergent angle compared with conventional LEDs,which is consistent with the results of finite-difference time-domain simulation.     

Improved light extraction efficiency and leakage characteristics in light-emitting diodes by nanorod arrays formed on hexagonal pits

We report the enhancement of light extraction efficiency (LEE) and electrical performance in GaN-based green light-emitting diodes (LEDs) using ZnO nanorods formed on the etched surface of p-GaN. Green LEDs with hybrid ZnO nanorod structures grown on the hexagonally etched topmost layer of the LEDs, show an improvement in electroluminescence intensity that is 3.5 times higher than LEDs without any other surface treatments. The improvement in LEE in LEDs with nanohybrid structures was confirmed by finite-difference time-domain simulation analysis. Besides LEE enhancement, the surface etching effects on the reduction of leakage current of fabricated LEDs were also investigated.     

用表面粗化ITO的欧姆接触提高GaN基LED性能

应用ICP干法刻蚀工艺和自然光刻技术,制备了ITO表面粗化的GaN基LED芯片。聚苯乙烯纳米颗粒在干法刻蚀中作为刻蚀掩膜。通过扫描电镜(SEM)观察ITO薄膜的粗糙度,并且报道了优化的粗化工艺参数。结果表明,ITO表面粗化的GaN基LED芯片同传统的表面光滑的芯片相比在20 mA的驱动电流下,发光强度提高了70%。