纳米压印技术制备表面光子晶体LED的研究

利用表面光子晶体能大幅提高发光二极管(LED)的外量子效率, 但如何制备大面积的纳米光子晶体是该研究方向的主要难点之一. 本文基于纳米压印技术在氮化镓基发光二极管(GaN-LED)表面制作孔状二维光子晶体. 通过以金属和聚合物双层掩膜干法刻蚀法, 得到了很好的光子晶体图形转移效果. 最终在LED的p-GaN层表面获得了大面积光子晶体, 周期为450 nm, 纳米孔直径为240 nm. 器件测试结果显示, 有表面光子晶体的LED比没有光子晶体的LED, 光致发光强度峰值提高到了7.2倍.     

SiO2图形化蓝宝石衬底对GaN生长及LED发光性能的影响

为了提高氮化镓(GaN)基发光二极管(LEDs)的发光性能,采用等离子体增强化学气相沉积(PECVD)在蓝宝石衬底上沉积SiO_2薄膜,经过光刻和干法刻蚀技术制备了SiO_2图形化蓝宝石衬底(SiO_2 patterned sapphire substrate, SPSS),利用LED器件的外延生长和微纳加工技术获得了基于SPSS的GaN基LED器件。通过分析GaN外延层晶体质量、光提取效率和LED器件性能,重点研究了SPSS对GaN生长及LED发光性能的影响。实验及模拟仿真结果表明,与常规图形化蓝宝石衬底(Conventional patterned sapphire substrate, CPSS)相比,SPSS上生长的GaN外延层位错密度较低,晶体质量较高,SPSS-LED的光提取效率提高26%、光输出功率和亮度均提高约5%。     

光子晶体结构参数的随机扰动对光子晶体LED出光效率的研究

利用光子晶体(PC)的光子禁带和光栅衍射效应可以提高发光二极管(LED)的出光效率,扩大LED的应用范围。在GaN基蓝光LED的GaN层上引入二维正方排列圆柱形PC,采用时域有限差分方法研究光子晶体的几何参数的随机扰动对LED出光效率的影响,利用禁带理论分析了其机理。     

柱状与孔状图形衬底对MOVPE生长GaN体材料及LED器件的影响

在柱状图形蓝宝石衬底（PSS-p）和孔状图形蓝宝石衬底（PSS-h）上外延了GaN体材料和LED结构并进行了详细对比和分析.X射线衍射仪（XRD）和原子力显微镜（AFM）测试结果表明,PSS-h上体材料的晶体质量和表面形貌都优于PSS-p上体材料的特性,通过断面扫面电子显微镜（SEM）照片看出PSS-h上GaN的侧向生长是导致这种差异的原因.另外,基于PSS-p和PSS-h上外延的LED材料制作而成的器件结果表明,其20?mA下光功率水平相比普通蓝宝石衬底（CSS）分别提高了46%和33%.通过变温光荧光 关键词： 蓝宝石图形衬底 氮化镓 发光二极管 侧向生长     

硅衬底GaN蓝色发光材料转移前后应力变化研究

利用外延片压焊和湿法腐蚀技术将硅衬底上生长的InGaN多量子阱发光二极管(LED)薄膜材料转移到了新衬底上. 研究结果表明, 转移后的LED薄膜中GaN层受到的张应力变小,InGaN层受的压应力变大. 去除转移后LED薄膜中过渡层后,GaN层受到的张应力变大,而铟镓氮层受到的压应力基本不变. 将转移后的薄膜做成垂直结构的LED芯片后,其光电性能明显改善. 关键词： GaN 发光二极管 硅衬底 应力     

引入n型InGaN/GaN超晶格层提高量子阱特性研究

利用金属有机物化学气相淀积技术在蓝宝石衬底上生长了InGaN/GaN量子阱结构. 研究了引入n型InGaN薄层或InGaN/GaN超晶格层的量子阱特性,结果表明通过引入n型InGaN薄层或InGaN/GaN超晶格层缓解了量子阱有源区中的应力,改善了多量子阱表面形貌,减少了V型缺陷密度,而且提高了多量子阱的光致发光强度,从而也改进了LED的发光效率. 关键词： InGaN/GaN多量子阱 原子力显微镜 X射线双晶衍射 光致发光     

高亮度白光LED用外延片的新进展

文章首先介绍了发光二极管（LED）的内量子效率、外量子效率的基本概念和提高量子效率的基本方法，接着对LED外延的结构和方法做了简要介绍．文章的第三和第四部分则着重介绍了提高内、外量子效率的外延方法，这些方法包括外延结构的优化，侧向外延生长，SiC和GaN衬底的生长，AIInGaN四元系有源区生长，非极性面、半极性面的外延，表面粗化结构生长，图形化二次外延结构．图形化蓝宝石衬底上的外延，提高载流子注入效率的结构和组分设计．文章的第五部分则介绍了基于可靠性和成本考虑的其他新型外延结构，第六部分介绍了提高LED可靠性的外延方法．最后得出结论：采用非极性面的GaN衬底，生长优化的LED结构，并结合光子晶体技术，可望取得突破性进展．     

400nm高性能紫光LED的制作与表征(英文)

利用金属有机物化学气相沉积技术在蓝宝石衬底表面制备了带有p-AlGaN电子阻挡层的400 nm高性能紫光InGaN多量子阱发光二极管。制作了3种紫光LED,分别带有不同p-AlGaN电子阻挡层结构:Al摩尔分数为9%的p-AlGaN电子阻挡层;Al摩尔分数为11%的p-AlGaN电子阻挡层;Al摩尔分数为20%的10对p-AlGaN/GaN超晶格电子阻挡层。带有高浓度Al电子阻挡层的紫光LED的光输出功率高于低浓度Al电子阻挡层的紫光LED。带有10对p-AlGaN/GaN超晶格电子阻挡层的紫光LED的光输出功率获得了极大的提高,在20 mA注入电流时测试得到的光输出功率为21 mW。此外,该LED同时显示了在高注入电流下接近线性的I-L特性曲线和在LED芯片表面均匀的发光强度分布。     

GaN基高压直流发光二极管制备及其性能分析

GaN基高压直流发光二极管工艺制备, 采用蓝宝石图形衬底(PSS) 外延片制备正梯形芯粒结构的GaN基高压直流LED.相对其他结构器件, 该结构器件发光效率最高, 封装白光后, 在色温4500 K, 驱动电流20 mA时, 光效116.06 lm/W, 对应电压50 V. 测试其I-V曲线表明, 开启电压为36 V, 对应驱动电流为1.5 mA; 在电流15 mA至50 mA时, 光功率随驱动电流增加近似于线性增加, 在此区域光效随电流增加而降低的幅度比较缓慢, 表明GaN基高压直流LED适宜于采用大电流密度驱动, 而不会出现驱动电流密度增加导致量子效率明显下降(efficiency droop), 为从芯片层面研究解决量子效率下降难题提供了一种新思路.     

GaN基LED倒装芯片蓝宝石衬底半球型图形优化设计

为了提高GaN基LED芯片的光提取效率,以GaN基LED芯片为研究对象,建立了在蓝宝石衬底出光面和外延生长面上具有半球型图形的LED倒装芯片模型,并利用光学仿真软件对图形参数进行优化设计。实验结果表明:在蓝宝石衬底的出光面和外延生长面双面都制作凹半球型图形对芯片光提取效率的提高效果最好,并且当半球的半径为3 m,周期间距为7 m时,GaN基LED倒装芯片的最大光提取效率为50.8%,比无图形化倒装芯片的光提取效率提高了115.3%。     

Enhanced Photoluminescence of InGaN/GaN Green Light-Emitting Diodes Grown on Patterned Sapphire Substrate

Green InGaN/GaN based light-emitting diodes （LEDs） are fabricated both on planar and wet-etched patterned sapphire substrates by metalorganic vapour phase epitaxy （MOVPE）. Their photoluminescence （PL） properties of the two samples are studied. The results indicate that the PL integral intensity of the green LED on the patterned substrate is nearly two times of that on the planar one within the whole measured temperature range. The enhanced PL intensity in the green LED on the patterned substrate is shown completely contributed from the extraction efficiency, but not from the internal quantum efficiency. The conclusion is supported by temperature-dependent PL analysis on the two samples, and the mechanisms axe discussed.     

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates(PSSes) with different values of fill factor(f) and slanted angle(θ) are investigated in detail.The threading dislocation(TD) density is lower in the film grown on the PSS with a smaller fill factor,resulting in a higher internal quantum efficiency(IQE).Also the ability of the LED to withstand the electrostatic discharge(ESD) increases as the fill factor decreases.The illumination output power of the LED is affected by both θ and f.It is found that the illumination output power of the LED grown on the PSS with a lower production of tan θ and f is higher than that with a higher production of tan θ and f.     

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates (PSSes) with different values of fill factor (f) and slanted angle (θ) are investigated in detail. The threading dislocation (TD) density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency (IQE). Also the ability of the LED to withstand the electrostatic discharge (ESD) increases as the fill factor decreases. The illumination output power of the LED is affected by both θ and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tanθ and f is higher than that with a higher production of tanθ and f.     

Simulation of InGaN/GaN light-emitting diodes with patterned sapphire substrate

Blue InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with patterned sapphire substrate (PSS) are simulated by the APSYS software. Approach of combining finite-difference time-domain (FDTD) method and raytracing technique is applied to perform light extraction. The simulation results show that PSS dramatically increases extraction efficiency of light power, in agreement with experiment. It is found that extraction efficiency can be maximized by changing the shape of PSS. This work presents a new approach to combine electrical simulation with FDTD and raytracing in 3D TCAD simulation of GaN-LED.     

Si衬底GaN基LED的结温特性

结温是发光二极管的重要参数之一,它对器件的内量子效率、输出功率、可靠性及LED的其他一些性能有很大的影响。首次报道Si衬底GaN基LED的结温特性。利用正向压降法测量Si衬底上GaN基LED的结温,通过与蓝宝石衬底上GaNLED的结温比较,发现Si衬底GaNLED有更低的结温,原因归结为Si有更好的导热性。同时也表明:用Si作GaNLED的衬底在大功率LED方面具有更大的应用潜力。     

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。     

Air-gap embedding GaN template for enhanced emission from light-emitting diodes

Selective growth by metal-organic chemical vapor deposition (MOCVD), and electrochemical etching of a heavily Si-doped GaN (n⁺-GaN) interlayer were employed to obtain air-gaps embedded in a u-GaN layer. As confirmed by Raman spectroscopy, the introduction of an n⁺-GaN, which was later etched to obtain air-gaps, also enhanced the strain-compliance of GaN epilayer on sapphire substrate. An enhanced electroluminescence emission was observed from the light-emitting diodes (LEDs) fabricated on the air-gap embedding template. Using theoretical LED simulation, it was discerned that the increase in optical emission from the LED was caused predominantly by the redirection of photons at GaN/air-gap interface. Finite-difference time domain (FDTD) simulation method was employed to understand the mechanism of optical emission enhancement and its spatial variation over the LED surface.     

Forming the graded-refractive-index antireflection layers on light-emitting diodes to enhance the light extraction

Distributed antireflection (AR) layers with different composition ratios of ITO and SiO(2) formed on an ITO electrode of GaN-based LEDs provide substantial enhancement in light-extraction efficiency. By using the coradio frequency magnetron sputtering deposition, four 50 nm thick AR layers with graduated refractive indices were fabricated. The effect of the AR layers on enhancing the efficiency of the LED device was analyzed by electroluminescence (EL) and I-V measurements. As a result, the EL intensity of the LED device grown on the patterned sapphire substrate with AR layers was increased by up to 13% compared to the conventional patterned sapphire substrate-applied LED device without AR layers at a drive current of 20 mA. The AR layers on top of the LED device gradually changed the refractive indices between ITO (n=2.1) and air (n=1.0), which minimized the total internal reflection of generated light. And no degradation in the electrical characteristic of the LEDs was observed according to the I-V measurements.     

硅衬底氮化镓基LED薄膜转移至柔性黏结层基板后其应力及发光性能变化的研究

本文将硅(Si)衬底上外延生长的氮化镓(GaN)基发光二极管(LED)薄膜转移至含有柔性黏结层的基板上, 获得了不受衬底和支撑基板束缚的LED薄膜. 利用高分辨率X射线衍射仪(HRXRD)研究了薄膜转移前后的应力变化, 同时对其光致发光(PL)光谱的特性进行了研究. 结果表明: 硅衬底GaN基LED薄膜转移至柔性基板后, GaN受到的应力会由转移前巨大的张应力变为转移后微小的压应力, InGaN/GaN量子阱受到的压应力则增大; 尽管LED薄膜室温无损转移至柔性基板其InGaN阱层的In组分不会改变, 然而按照HRXRD倒易空间图谱通用计算方法会得出平均铟组发生了变化; GaN基LED薄膜从外延片转移至柔性基板时其PL谱会发生明显红移.