Improved light extraction of wafer-bonded AIGaInP LEDs by surface roughening

By using the wafer bonding technique and wet etching process, a wafer bonded thin film AlGaInP LED with wet etched n-AlGaInP surfaces was fabricated. The morphology of the etched surface exhibits a pyramid-like feature. The wafer was cut into 270× 270 μm2 chips and then packaged into TO-18 without epoxy resin. With 20-mA current injection, the light intensity and output power of LED-I with surface roughening respectively reach 315 mcd and 4.622 mW, which was 1.7 times higher than that of LED-II without surface roughening. The enhancement of output power in LED-I can be attributed to the pyramid-like surface, which not only reduces the total internal reflection at the semiconductor-air interface but also effectively guides more photons into the escape angle for emission from the LED device.     

表面粗化提高倒装AlGaInP发光二极管的光提取效率

对发光二极管进行表面粗化能够大幅度的提高其光提取效率。利用晶片键合技术并采用湿法刻蚀的办法粗化n面AlGaInP表面制作了一种带表面粗化的倒装薄膜发光二极管。刻蚀后的表面形貌呈现金字塔状。270μm x 270μm管芯裸装在TO-18金属管座上,在20mA的注入电流下,粗化了的LED-I光强达到了315mcd,输出光功率达到了4.622mW,比没有粗化的LED-II的光功率高1.7倍。光功率增加的原因在于粗化后形成的这种金字塔状表面,其不但减少了背部镜面系统和半导体-空气接触面的反射,而且能有效的将光从LED中散射出去。     

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,...     

具有纳米级结构出光面的AlGaInP基发光二极管

研究了一种利用金属自组装纳米掩膜和ICP刻蚀对AlGaInP基发光二极管(LED)表面进行粗化的技术,使光输出得到了提高.粗化了的AlGaInP基LED比常规的AlGaInP基LED,光强提高了27%,光功率提高了12.6%,实验结果具有可重复性.可以进一步优化Au颗粒的周期和分散程度,提高AlGaInP基LED的提取效率.     

晶圆键合技术在LED应用中的研究进展

简要介绍了晶圆键合技术在发光二极管(LED)应用中的研究背景,分别论述了常用的黏合剂键合技术、金属键合技术和直接键合技术在高亮度垂直LED制备中的研究现状,包括它们的材料组成和作用、工艺步骤和参数以及优缺点.其中,黏合剂键合是一种低温键合技术,且易于应用、成本低、引入应力小,但可靠性较差;金属键合技术能提供高热导、高电导的稳定键合界面,与后续工艺兼容性好,但键合温度高,引入应力大,易造成晶圆损伤;表面活化直接键合技术能实现室温键合,降低由于不同材料间热失配带来的负面影响,但键合良率有待提高.     

Increasing the extraction efficiency of AlGaInP LEDs via n-side surface roughening

An n-side-up AlGaInP-based light-emitting diode (LED) with a triangle-like surface morphology was fabricated using the adhesive layer bonding technique, followed by wet etching to roughen the surface. The light output power of the roughened-surface LED was 1.6 times higher than that of a flat-surface LED at an injection current of 20 mA, i.e., a significant improvement attributed to the ability of the roughened surface to not only reduce the internal reflection between the rear mirror system and the semiconductor-air interface, but also to effectively scatter the light outside the LED device.     

新型表面再构的倒装AlGaInP LED

研究一种表面再构的具有全方位反光镜(ODR)结构的倒装AlGaInP半导体发光二极管(LED)。通过湿法腐蚀方法再构N-AlGaInP盖层表面,形成类金字塔的表面结构,使不同角度入射的光有更多的机会出射。比较了表面再构LED与常规LED的电、光学特性,在注入电流为20 mA时,经过表面再构LED的轴向光强和输出光功率是常规LED的1.5倍,表面再构后大大提高了LED的外量子效率,减少了LED内部热量的积累,提高了LED芯片的可靠性。     

Reliability of AlGaInP light emitting diodes with an ITO current spreading layer

Three aging experiments were performed for AlGalnP light emitting diodes (LED) with or without indium tin oxide (ITO), which is used as a current spreading layer. It was found that the voltage of the LED with an ITO film increased at a high current stressing, while there was little change for that of the LED without the ITO. The results of the LEDs with different thicknesses of the ITO film show that the LED with a thicker ITO has a higher reliability. The main reason for the voltage increase of the LED with the ITO film might be the current crowding in the ITO film around the P-type electrode.     

A Spacer Cation Assisted Nucleation and Growth Strategy Enables Efficient and High-Luminance Quasi-2D Perovskite LEDs

Quasi-2D Ruddlesden-Popper perovskites receive tremendous attention for application in light-emitting diodes (LEDs). However, the role of organic ammonium spacers on perovskite film has not been fully-understood. Herein, a spacer cation assisted perovskite nucleation and growth strategy, where guanidinium (GA⁺) spacer is introduced into the perovskite precursor and at the interface between the hole transport layer (HTL) and the perovskite, to achieve dense and uniform perovskite films with enhanced optical and electrical performance is developed. A thin GABr interface pre-formed on HTL provides more nucleation sites for perovskite crystal; while the added GA⁺ in perovskite reduces the crystallization rate due to strong hydrogen bonding interacts with intermediates, which promotes the growth of enhanced-quality quasi-2D perovskite films. The ionized ammonium group ( NH₃⁺) of GA⁺ also favors formation of polydisperse domain distribution, and amine or imine ( NH₂ or NH) group interact with perovskite defects through coordination bonding. The spacer cation assisted nucleation and growth strategy is advantageous for producing efficient and high-luminance perovskite LEDs, with a peak external quantum efficiency of over 20% and a luminance up to 100 000 cd m⁻². This work can inform and underpin future development of high-performance perovskite LEDs with concurrent high efficiency and brightness.     

Polymer-based scattering layers for internal light extraction from organic light emitting diodes

Efficient light extraction for organic light emitting diodes (OLED) using scalable processes and low-cost materials are important prerequisites for the future commercialization of OLED lighting devices. The light-extraction technology exhibited in this paper uses polymer-based high-refractive index scattering layers processed from solution. The scatter matrix formulation incorporates two types of nanoparticles for refractive index tuning and scattering, respectively. Planarization by the same material in order to reduce surface defects was critical for achieving highly increased device yield. Highly efficient and defect-free large-area (1.8 cm²) white OLED devices were fabricated on top of the scattering layer in a bottom emitter configuration. Light extraction enhancement leads to an overall efficiency gain of up to 81% for luminances of 5000 cd m⁻².     

发光二极管中负电容现象的机理

为解释发光二极管（LEDs）中的负电容（NC）现象,提出了在有源区与局部强复合效应有关的新模型,首次通过对载流子连续性方程的求解导出了NC的解析表达式。理论结果表明,在一定的范围内激活区载流子复合速率越大,LEDs中的NC效应越显著,这与实验结果完全一致。它表明,LEDs中的NC是由其激活区载流子复合引起的,而非外部原因造成。     

Improved light extraction in AlGaInP-based LEDs using a self-assembly metal nanomask

This paper reports a new method of fabricating AIGaInP-based nanorod light emitting diodes (LEDs) by using self-assembly metal layer nanomasks and inductively coupled plasma.Light-power measurements indicate that the scattering of photons considerably enhances the probability of escaping from the nanorod LEDs.The light-intensity of the nanorod LED is increased by 34% for a thin GaP window layer,and by 17% for an 8μm GaP window layer.The light-power of the nanorod LED is increased by 25% and 13%,respectively.     

自制纳米金属掩模对AlGaInPLED光提取效率的改进

In conventional light-emitting diodes (LED’s), the external efficiency is limited by total internal reflection at the semiconductor-air interface. An LED with a textured top surface can increase the light-extraction efficiency. This paper reports a new method to fabricate AlGaInP-based nanorod light emitting diodes (LEDs) by using self-assemble metal layer nano-masks and inductively coupled plasma (ICP). Light power measurements indicates that the scattering of photons considerably enhance the probability of escaping from the nanorod LEDs. The light-intensity of the nanorod LED is increased by 34% for a thin GaP window layer, and by 17% for 8 μm GaP window layer. The light power of the nanorod LED is increased by 25% and 13%, respectively.     

具有纳米凹坑氧化铟锡的LED光提取效率的提高

由于低的光提取效率,氮化镓基发光二极管的应用受到了限制。氧化铟锡—氮化镓界面的光的全反射作用是造成低的光提取效率的重要原因。人们提供了多种方法来提高光提取效率。本文揭示了一种简单并且经济的方法。通过自组装和干法刻蚀的方法制作粗化的氧化铟锡薄膜。运用原子力显微镜（AFM）对表面形态和粗糙程度进行观察。测量各个样品的I-V特性、出光功率和出光辐射图并进行对比。刻蚀之后,在ITO表面形成了圆柱体和凹坑结构,它们的高度随着刻蚀时间增大。结果显示,LED的出光功率和随着刻蚀时间的增加而增加。由于圆柱体和凹坑结构的形成以及它们深度的增加,ITO-GaN界面的光的全反射减少了。因此,出光率提高。     

阳极氧化铝工艺用于提高LED的出光效率

使用纳米尺度的多孔阳极氧化铝(anodic aluminum oxide,AAO)作为刻蚀掩膜,刻蚀氧化铟锡(indium-tin oxide,ITO),形成纳米图形化表面,对于发光二极管的出光效率有明显的提升作用。AAO纳米掩膜的制备已广为报道,是纳电子学研究中常用的模板之一,工艺简单易行、可控性好。使用电感耦合反应离子刻蚀方法成功将纳米多孔结构转移到ITO上,形成ITO纳米结构。纳米图形化结构的引入使得器件有效减小了内部的全反射,在电压没有大幅提高,注入电流350 mA时,光学输出提高了7%。纳米尺度粗化结构LED与传统结构LED对比,提升了器件的外量子效率。     

表面粗化对GaN基垂直结构LED出光效率的影响

用加热后的KOH水溶液腐蚀GaN材料的N极性面,用以提高GaN基垂直结构发光二极管(LED)的出光效率。经过湿法腐蚀后,构成N极性面的表面晶粒尺寸和密度成为影响垂直结构LED提取效率的主要因素,通过分析不同腐蚀条件下晶粒尺寸和密度与出光效率间的关系,得到最优化的粗化条件,使得器件的提取效率达到最佳。经由浓度为30%、温度为60℃的KOH溶液腐蚀后,未封装的垂直结构LED芯片的提取效率增加了近1倍。     

Evaluation of light extraction efficiency for the light-emitting diodes based on the transfer matrix formalism and ray-tracing method

The internal quantum efficiency (IQE) of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency (EQE) and the light extraction efficiency (LEE). The EQE can be measured experimentally, but the LEE is difficult to calculate due to the complicated LED structures. In this work, a model was established to calculate the LEE by combining the transfer matrix formalism and an in-plane ray tracing method. With the calculated LEE, the IQE was determined and made a good agreement with that obtained by the ABC model and temperature-dependent photoluminescence method. The proposed method makes the determination of the IQE more practical and conventional.     

Realizing improved performance of down-conversion white organic light-emitting diodes by localized surface plasmon resonance effect of Ag nanoparticles

Down-conversion structure white organic light-emitting diodes (WOLEDs), in which white light is generated by a blue emission organic light-emitting diodes (OLEDs) in combination with a color conversion layer (CCL) outside the substrate, has attracted extensive interest due to its significant advantages in low cost and stabilized white-light emissions. However, low color-conversion efficiency of CCL is still a bottleneck for the performance improvement of down-conversion WOLEDs. Here, we demonstrate an approach to enhance the color-conversion efficiency of CCL-WOLEDs by localized surface plasmon resonance (LSPR) effect. In this approach, a blend of Ag nanoparticles and polyvinyl alcohol (PVA) is solution-deposited between the blue organic light emitting diodes and color-conversion layer. Based on the LSPR effect of this modified structure, the color conversion efficiency has improved 32%, from 45.4% to 60%, resulting a 14.4% enhancement of the current efficiency, from 9.73 cd/A to 11.14 cd/A. Our work provides a simple and low-cost way to enhance the performance of down-conversion WOLEDs, which highlights its potential in illumination applications.     

Corrugated structure through a spin-coating process for enhanced light extraction from organic light-emitting diodes

We have demonstrated a simple fabrication method for an out-coupling structure to enhance light extraction from organic light-emitting diodes (OLEDs). Spin-coating of SiO₂ and TiO_x sol mixture solution develops corrugated film. The structural evolution of the corrugation was explained by the localization of surface tension during the solvent evaporation. The structural parameters of the corrugated structure were characterized by varying the spin-coating speed and the mixing ratio of the solution. Compared to conventional devices, OLEDs with a corrugated structure at the backside of the glass substrate showed increased external quantum efficiency without change in the electroluminescence spectrum. The light extraction enhancement is attributed to the decreased incidence angle at the interface of glass substrate and air.     

Prism coupling method to evaluate the light extraction efficiency of outcoupling substrates

One of the key challenges in organic light-emitting diodes (OLEDs) for lighting applications is efficient light extraction from the planar, multi-layered OLED stack. Several different light extraction approaches are being explored currently by researchers, however characterizing light extraction films after fabricating OLEDs is not a viable approach when the outcoupling films have large surface roughness and is time consuming as well. Here we apply prism coupling method (PCM), a simple and elegant tool, to characterize outcoupling films. We show the effectiveness of PCM in estimating light extraction efficiency of outcoupling films. PCM can expedite selection and optimization of various light extraction approaches without the need to build OLEDs. The experimental results are corroborated by the optical simulations done using ray tracing method taking into account Mie scattering from wavelength sized spherical inclusions in an outcoupling film.