图形化蓝宝石衬底形貌对GaN基LED出光性能的影响

近年来,图形化蓝宝石衬底(PSS)作为GaN基LED外延衬底材料被广泛应用.通过干法刻蚀和湿法腐蚀制备了不同规格和形状的蓝宝石衬底图形,并进行外延生长、芯片制备和封装验证,采用扫描电子显微镜(SEM)和3D轮廓仪进行形貌表征,研究了不同规格和形状的衬底图形对LED芯片出光性能影响,并与外购锥形衬底(PSSZ2)进行对比.结果表明,在20 mA工作电流下,PSSZ2的LED光通量为8.33 lm.采用类三角锥和盾形衬底的LED光通量分别为7.83 lm和7.67 lm,分别比PSSZ2衬底低6.00％和7.92％.对锥形形貌进行优化,采用高1.69 μm、直径2.62 μm、间距0.42 μm的锥形衬底(PSSZ3)的LED光通量为8.67 lm,比PSSZ2衬底高4.08％,优化的PSSZ3能有效地提高LED出光性能.     

高亮度高纯度白光LED封装技术研究

通过对高功率InGaN(蓝)LED倒装芯片结构+YAG荧光粉构成白光LED的分析,可以得出这种结构能提高发光效率和散热效果的结论。通过对白光LED的构成和电流/温度/光通量的分析,可知在蓝宝石衬底和环氧树脂的界面间涂敷一层硅橡胶能改善光的折射率。改进光学器件的封装技术,可以大幅度提高大功率LED的出光率(光通量)。     

BiCaInVIG法拉第旋转器旋光色散的测量

对于法拉第光隔离器,法拉第旋转器45°旋转角的精确度决定了其隔离度,法拉第旋转器的旋光色散决定了其带宽。本文给出了法拉第旋转器旋光色散的测量方法,并对铋钙钒石榴石(BiCaInVIG)法拉第旋转器样品的旋光色散进行了测量。结果表明:波长越长,法拉第旋转角越小。     

LED汽车前照灯高效抛物反射器的研究

根据非成像光学和光度学理论,针对LED光源的发光特性和汽车造型设计要求,分析了影响抛物反射器能量利用率的几何参数,导出了抛物反射器的光能利用率与反射器的口径、收光角及抛物镜主轴相对LED光源的角度的解析关系式.分析结果表明,反射器单位口径的光能利用率随口径的变化并非单调,而是存在着峰值,当收光角为70.53°时,单位口径收光效率最大值;对一定光学扩展量的抛物反射器,通过旋转LED光源,可以进一步提高光能利用率;抛物反射器的收光角不同,最佳的旋转角度也不同.TracePro仿真模拟结果与理论分析结论基本一致,所得结果为抛物反射器的优化设计提供了理论依据.     

折射率匹配对绿光发光二极管微显示光学性能影响

设计了用于发光二极管(LED)微显示器折射率匹配层结构,可以提高LED微显示器的光学性能。倒装结构的LED微显示器出光面为蓝宝石(折射率约1.76),它和空气的折射率(约为1.0)相差较大,会有很大一部分光因为全反射而反射回器件内部被吸收,导致器件的光效率降低。本文通过涂敷折射率匹配层硅胶(折射率约1.41～1.53)的方法,改变器件表层的折射率使其和空气的折射率相匹配,增加光逃逸锥角,从而提高器件的光效率。结果表明涂敷硅胶可以提高光效率约25.75%,在涂敷硅胶基础上盖玻璃片(折射率约1.47)可提高光效率约32.78%,且硅胶涂敷前后器件的电学、光学、结温稳定性好。尽管增加的是侧方向的光通量,但是其光效率的增加为高效率LED微显示的实现提供了参考依据。     

带有锥状反射结构的AlGaInP键合衬底LED

本研究通过光辅助化学腐蚀技术在衬底键合AlGaInP反极性发光二极管中制备出锥状反射镜结构提升器件的光提取效率。首先利用氢氟酸与双氧水在532nm激光的辐射下载GaP:Mg层制备出锥状腐蚀结构,然后将金属反射镜蒸镀在锥状结构之上制备锥状的反射镜结构。在完成全部芯片工艺后,测试结果表明锥状反射镜结构可以显著提升光提取效率,并在光通量测量中与表面粗化集成平板反射镜LED相比较,得到了18.55%的增强。     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的自光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层．采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr^3＋在433．6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44．8～59lm提高到了79．4～84．9lm．     

面向投影仪的LED阵列单位Etendue光通量的研究

基于各种结构LED芯片的出光特性,计算了得到的芯片及集成阵列实际的光学扩展量(Etendue),以此分析了面向投影仪光源的LED集成阵列在不同芯片间距和芯片厚度条件下的单位光学扩展量的光通量.结果表明,在面向LED投影仪的多芯片集成阵列光源中,使用剥离衬底的垂直结构芯片容易获得更高的单位Etendue光通量,从而有利于提高投影仪亮度.同时,对一种表面球形凹坑周期性微结构的倒装垂直结构LED芯片的集成阵列单位Etendue光通量进行了分析.在无封装的情况下,该结构芯片集成阵列的单位Etendue光通量较普通蓝宝石正装芯片和SiC倒装芯片的集成阵列分别高出164%和150%.     

高光效LED灯丝球泡灯的光学性能研究

基于板上芯片(COB)封装技术,提出了一种360°出光的新型发光二极管(LED)灯丝球泡灯,其封装基板采用透明基板.研究了不同封装材料及芯片对其LED光通量、光效和色温的影响.首先介绍了LED灯丝球泡灯的结构、优点,然后分析了影响LED光学性能的因素,最后进行相关性能测试.测得采用玻璃/蓝宝石基板封装的LED灯丝的光通量分别为467.29和471.69 lm;光效分别为110.06和111.79lm/W;显色指数分别为84.1和81.9.测试结果表明,采用透明基板封装的LED灯丝球泡灯不仅能有效调节色温,而且能显著提高LED的光通量、光效和显色指数.     

侧面粗化提高GaN基LED出光效率研究

通过对传统结构LED出光分析,提出采用侧面粗化来提高GaN基LED出光效率的方法,使用蒙特卡罗光子追踪方法对器件出光效率进行了模拟。结果表明:粗化侧面为三角状、底角为55°时出光效率最高,随机粗化可以获得比固定角度粗化更高的出光效率,同时降低材料的吸收系数可以提高LED的出光效率,在吸收系数为10/cm时,经过粗化后的LED出光效率可以达到46.1%。模拟结果证明侧面粗化可以较大地提高LED的出光效率。     

Improved Extraction Efficiency of Light-Emitting Diodes by Modifying Surface Roughness With Anodic Aluminum Oxide Film

An anodic alumina oxide (AAO) film with nano-roughening is added on the top window layer of AlGaInP light-emitting diodes (LEDs) to improve the light extraction of the device. The AAO film has a natural porosity to provide light scattering centers at the surface, allowing an increase of light emission intensity with no loss of or damage to the semiconductor material. Further, the fabricated AAO film with a refractive index is about which is intermediate between those of air and the window layer of GaP. By inserting this layer between the ambient and GaP, it broadens the critical angle for light emission and reduces internal reflection. Experiments with laboratory-fabricated AlGaInP devices of conventional design demonstrated a 32% improvement in the luminous intensity at 20 mA for the device with the AAO layer. This letter shows by theory and experiment that AAO films can be used as a low-cost, easily implemented surface nano-roughening for improving extraction efficiency of AlGaInP LEDs.     

Enhanced Light Extraction in GaInN Light-Emitting Diode With Pyramid Reflector

GaInN light-emitting diodes (LEDs) that employ a reflector consisting of an array of three-dimensional (3-D) SiO₂ pyramids and a Ag layer are demonstrated to have enhanced light extraction compared with GaInN LEDs with planar Ag reflector. Ray tracing simulations reveal that the pyramid reflector provides 14.1% enhancement in extraction efficiency. Consistent with the simulation, it is experimentally demonstrated that GaInN LEDs with the pyramid reflector show 13.9% higher light output than LEDs with a planar Ag reflector. The enhancement is attributed to the appearance of an additional escape cone for light extraction enabled by the 3-D pyramid reflector     

Increased effective reflection and transmission at the GaN-sapphire interface of LEDs grown on patterned sapphire substrates

The effect of patterned sapphire substrate (PSS) on the top-surface (P-GaN-surface) and the bottom-surface (sapphire-surface) of the light output power (LOP) of GaN-based LEDs was investigated, in order to study the changes in reflection and transmission of the GaN-sapphire interface. Experimental research and computer simulations were combined to reveal a great enhancement in LOP from either the top or bottom surface of GaN-based LEDs, which are prepared on patterned sapphire substrates (PSS-LEDs). Furthermore, the results were compared to those of the conventional LEDs prepared on the planar sapphire substrates (CSS-LEDs). A detailed theoretical analysis was also presented to further support the explanation for the increase in both the effective reflection and transmission of PSS-GaN interface layers and to explain the causes of increased LOP values. Moreover, the bottom-surface of the PSS-LED chip shows slightly increased light output performance when compared to that of the top-surface. Therefore, the light extraction efficiency (LEE) can be further enhanced by integrating the method of PSS and flip-chip structure design.     

AlGaInP系LED的表面纳米级粗化以及光提取效率提高

分析了常规AlGaInP系发光二极管（LED）光提取效率低的主要原因,半导体的折射率与空气折射率相差很大,导致全反射使有源区产生的光子绝大部分不能通过出光面发射到体外。通过在LED出光层采用纳米压印技术引入表面纳米结构,以改变光子的传播路径,从而使得更多的光子能够发射到体外。理论分析与实验结果表明,与常规平面结构相比,...     

Enhancement of Light Extraction Through the Wave‐Guiding Effect of ZnO Sub‐microrods in InGaN Blue Light‐Emitting Diodes

The improvement of the light extraction efficiency (LEE) of a conventional InGaN blue light‐emitting diode (LED) by the incorporation of one‐dimensional ZnO sub‐microrods is reported. The LEE is improved by 31% through the wave‐guiding effect of ZnO sub‐microrods compared to LEDs without the sub‐microrods. Different types of ZnO microrods/sub‐microrods are produced using a simple non‐catalytic wet chemical growth method at a low temperature (90 °C) on an indium‐tin‐oxide (ITO) top contact layer with no seed layer. The crystal morphologies of needle‐like or flat‐top hexagonal structures, and the ZnO microrods/sub‐microrod density and size are easily modified by controlling the pH value and growth time. The wave‐guiding phenomenon within the ZnO rods is observed using confocal scanning electroluminescence microscopy and micro‐electroluminescence spectra.     

Failure and degradation mechanisms of high-power white light emitting diodes

The investigation explores the factors that influence the long-term performance of high-power 1 W white light emitting diodes (LEDs). LEDs underwent an aging test in which they were exposed to various temperatures and electrical currents, to identify both their degradation mechanisms and the limitations of the LED chip and package materials. The degradation rates of luminous flux increased with electrical and thermal stresses. High electric stress induced surface and bulk defects in the LED chip during short-term aging, which rapidly increased the leakage current. Yellowing and cracking of the encapsulating lens were also important in package degradation at 0.7 A/85 °C and 0.7 A/55 °C. This degradation reduced the light extraction efficiency to an extent that is strongly related to junction temperature and the period of aging. Junction temperatures were measured at various stresses to determine the thermal contribution and the degradation mechanisms. The results provided a complete understanding of the degradation mechanisms of both chip and package, which is useful in designing highly reliable and long-lifetime LEDs.     

Fabrication of Efficient Light-Emitting Diodes With a Self-Assembled Photonic Crystal Array of Polystyrene Nanoparticles

A low-cost method of fabricating large photonic crystal arrays of hexagonal posts without the use of lithography is described, along with an application of enhancing light extraction efficiency in semiconductor light-emitting diodes (LEDs). Polystyrene spheres are deposited onto a wafer surface and then processed to achieve control over photonic crystal lattice properties in a method suitable for fast and repeatable patterning. The spheres serve as an etch mask to extend the photonic crystal formed into the semiconductor surface. This technique is applied to LEDs to increase the top surface light extraction, and 51% wall plug enhancement is demonstrated in deep junction liquid phase epitaxially grown LEDs with absorbing substrates, though is adaptable to any substrate and photonic crystal dimensions.     

Calculation of LED modules for highway lighting

The calculated distributions of the highway illuminance provided by light-emitting diode (LED) modules that can be used in available supports and arms are presented. Different variants of the arms with LEDs characterized by various luminous intensity curves and emission angles of 10 to 100° are investigated. Rotation of LEDs with various luminous fluxes at a luminous efficiency of 100 lm/W is also considered.     

100-lm/W InGaAlP Thin-Film Light-Emitting Diodes With Buried Microreflectors

Thin-film light-emitting diodes (LEDs) belong to the most successful LED concepts for achieving high efficiencies. The incorporation of buried microreflectors with inclined facets prevents the light generation under the top contact and bondpad and offers an additional light extraction scheme. As a result, an external quantum efficiency of 50% could be demonstrated at a wavelength of 650 nm, and a luminous efficiency of more than 100 lm/W could be achieved in the wavelength range from 595 to 620 nm