Optical design and optimization of light emitting diode automotive head light with digital micromirror device light emitting diode

This research proposes a new method for light emitting diode automotive headlight design with digital micromirror device (DMD). The optical design is advanced because of the following features. First, this optical design controls the angle of light pattern without light masking so as to achieve much higher light efficiency compared with traditional optical design for headlight systems. Second, in view of the tendency that the advanced light emitting diode automobile headlight is designed to be a low beam light module and a high beam light still needs an auxiliary lighting system, the optical system designed in this research, mainly adopting DMD module as high/low beam light switch, can switch on and off both the high and low beam lights. Because DMDs function of accepting a bidimensional image, high/low beam light patterns can be determined by DMD. Third, a light pattern will be created and compensated simultaneously by DMD, which might replace mechanical adaptive front-lighting system in the future because DMD takes advantage of fast response and simultaneous compensation. Fourth, a design using a multiple reflection curved mirror is employed in this research to adjust light energy distribution; therefore, the articulation of the light pattern can be enhanced. For this method, experimental results of light efficiency are up to 85%, which is superior to current products in the market.     

Quantum dot light emitting diodes using size-controlled ZnO NPs

The particle size and trap energy level of ZnO were adjusted by varying the concentration of precursors using a sol–gel process, and the energy transport properties of the electron transport layer in quantum dot light-emitting diodes (QD-LEDs) were analyzed. Thus far, no study has considered the efficient electron transport properties of quantum dot light-emitting devices with respect to trap energy levels owing to the oxygen vacancies of ZnO. The particle size and trap energy levels of ZnO were analyzed based on optical properties such as photoluminescence and absorbance. The optimized device showed excellent performance, with a maximum luminance of 50,120 cd/m², a high efficiency of 5.85 cd/A, and a threshold voltage of 2.5 V. The Y-ZnO (yellow photoluminescence ZnO)-based QD-LEDs not only enhanced the injection efficiency of electrons into the emitting layer but also confined the holes in the emitting layer due to the shallow trap level of Y-ZnO, in contrast to the deep trap levels of G-ZnO (green photoluminescence ZnO) and B-ZnO (blue photoluminescence ZnO). Here, we present the first attempt to analyze the electron transport behavior of the electron transport layer of the resulting device.     

InGaN green light emitting diodes with deposited nanoparticles

We grew an InGaN/GaN-based light-emitting diode (LED) wafer by metal–organic chemical vapor deposition (MOCVD), fabricated devices by optical lithography, and successfully deposited ellipsoidal Ag nano-particles by way of e-beam lithography on top. The diodes exhibited good device performance, in which we expected an enhancement of the radiated intensity by the simulations and emission measurements. The obtained results showed the feasibility of plasmon-assisted LED emission enhancement.     

发光二极管可靠性的噪声表征

通过对发光二极管内部结构的研究，发现N_t(界面态陷阱密度)和扩散电流比率 是影响发光二极管性能的重要因素，并与器件可靠性有密切关系.器件内部存在的多种噪声 中，低频1/f噪声可表征N_t和扩散电流比率.在深入研究发光二极管工作原理及1 /f噪声载流子数涨落理论和迁移率涨落理论的基础上，建立了发光二极管的电性能模型及1/ f噪声模型.在输入电流宽范围变化的条件下测量了器件的电学噪声，实验结果与理论模型符 合良好.通过对其测量结果分析，深入研究了噪声和发光二极管性能与可靠性的关系，证明 了噪声幅值越大，电流指数越接近于2，器件可靠性越差，失效率则显著增大. 关键词： 1/f噪声 发光二极管 陷阱 光功率     

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.     

Blue light emitting diode exceeding 100% quantum efficiency

InGaN/GaN light‐emitting diodes (LEDs) are known to exhibit a strongly non‐uniform vertical carrier distribution within the multi‐quantum well (MQW) active region. We propose to eliminate “dark” quantum wells by insertion of multiple tunnel junctions into the MQW which allow for the repeated use of electrons and holes for photon generation. In good agreement with available measurements, we demonstrate by self‐consistent numerical simulation that such tunnel junction LED design promises quantum efficiencies as high as 250% as well as a strongly enhanced output power at high input power, compared to conventional LED concepts.

     

新型全方位反射铝镓铟磷薄膜发光二极管

提出了一种新型全方位反射铝镓铟磷(AlGaInP)薄膜发光二极管(LED)的结构和制作工艺，在这个结构里应用了低折射率的介质和高反射率的金属联合作为反光镜.用金锡合金(80Au20Sn，重量比)作为焊料把带有反光镜的AlGaInP LED外延片倒装键合到GaAs基板上(RS-LED)，去掉外延片GaAs衬底，把被GaAS衬底吸收的光反射出去.通过与常规AlGaInP 吸收衬底LEDs(AS-LED)和带有DBR的AlGaInP 吸收衬底LEDs(AS-LED(DBR))电、光特性的比较，证明新型全方位反射AlGaInP薄膜LED结构能极大提高亮度和效率.正向电流20mA时，RS-LED的光输出功率和流明效率分别是AS-LED的3.2倍和2.2倍，是AS-LED(DBR)的2倍和1.5倍.RS-LED(20mA下峰值波长627nm)的轴向光强达到194.3mcd，是AS-LED(20mA下峰值波长624nm)轴向光强的2.8倍，是AS-LED(DBR)(20mA下峰值波长623nm)轴向光强的1.6倍. 关键词： 铝镓铟磷 薄膜发光管 全方位反射镜 发光强度     

硅衬底InGaN/GaN基蓝光发光二极管droop效应的研究

InGaN/GaN基阱垒结构LED当注入的电流密度较大时, LED的量子效率随注入电流密度增大而下降, 即droop效应.本文在Si (111)衬底上生长了 InGaN/GaN 基蓝光多量子阱结构的LED,通过将实验测量的光电性能曲线与利用ABC模型模拟的结果进行对比, 探讨了droop效应的成因.结果显示:温度下降会阻碍电流扩展和降低空穴浓度, 电子在阱中分布会越来越不平衡,阱中局部区域中因填充了势能越来越高的电子而溢出阱外, 从而使droop效应随着温度的降低在更小的电流密度下出现且更为严重, 不同温度下实验值与俄歇复合模型模拟的结果在高注入时趋势相反.这此结果表明,引起 droop效应的主因不是俄歇非辐射复合而是电子溢出,电子溢出的本质原因是载流子在阱中分布不均衡.     

Optical design of adjustable light emitting diode for different lighting requirements

<正>Light emitting diode(LED) sources have been widely used for illumination.Optical design,especially freedom compact lens design is necessary to make LED sources applied in lighting industry,such as large-range interior lighting and small-range condensed lighting.For different lighting requirements,the size of target planes should be variable.In our paper we provide a method to design freedom lens according to the energy conservation law and Snell law through establishing energy mapping between the luminous flux emitted by a Lambertian LED source and a certain area of the target plane.The algorithm of our design can easily change the radius of each circular target plane,which makes the size of the target plane adjustable.Ray-tracing software Tracepro is used to validate the illuminance maps and polar-distribution maps.We design lenses for different sizes of target planes to meet specific lighting requirements.     

ZnO nanorods–polymer hybrid white light emitting diode grown on a disposable paper substrate

We demonstrate intrinsic white light emission from hybrid light emitting diodes fabricated using an inorganic–organic hybrid junction grown at 50 °C on a paper substrate. Cyclotene was first spin coated on the entire substrate to act as a surface barrier layer for water and other nutrient solutions. The active area of the fabricated light emitting diode (LED) consists of zinc oxide nanorods (ZnO NRs) and a poly(9,9‐dioctylfluorene) (PFO) conducting polymer layer. The fabricated LED shows clear rectifying behavior and a broad band electroluminescence (EL) peak covering the whole visible spectrum range from 420 nm to 780 nm. The color rendering index (CRI) was calculated to be 94 and the correlated color temperature (CCT) of the LED was 3660 K. The low process temperature and procedure in this work enables the use of paper substrate for the fabrication of low cost ZnO–polymer white LEDs for applications requiring flexible/disposable electronic devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

室内可见光通信发光二极管阵列发射性能的研究

提出了一种基于Lambert辐射模型的发光二极管光源阵列发射天线光照度计算模型,对室内可见光通信发射天线进行了优化设计.分析了光源的空间分布形式、光源间距、光源中心光束与系统光轴夹角以及空间分布层间距等因素对光照度均匀性的影响.通过仿真模拟和分析,得到了圆形阵列天线在照度均匀性和通信传输信号稳定性方面都优于相同光源数目的矩形阵列天线,并且提高了10%左右;同时得出了在满足室内照明情形下,发光二极管阵列发射天线照度均匀度随光源间距及光源中心光束与系统光轴夹角的增加均呈现出先增加后减小的变化趋势,因此,光源间距和光源中心光束与系统光轴夹角均存在最优值;照度均匀度随空间分布层间距的减小而增加,并给出了5 m×5 m×3 m普通房间内发射天线阵列设计参数的最优值,使发射性能得到了优化,同时节省光源数13%,降低了成本.这些研究为发射天线系统的设计提供了理论依据,具有实用价值.     

透镜对1W白光LED参数的影响

研究了透镜对1W白光LED光强空间分布、光通量和色温光参数的影响。研究结果表明,透镜是1W白光LED光强空间分布的决定因素,透镜的存在和选择性吸收导致1W白光LED发光效率和色温值下降。根据研究结果提出了一种不使用透镜的硅胶倒模封装形式,该封装形式的1W白光LED发光效率比有透镜时提高了6%~7%,且可以使用波峰焊和回流焊方式进行焊接。     

热真空环境下LED发光效率的实验研究

为了研究LED的发光效率在实际空间环境下的变化,对LED的发光效率在热真空环境下进行实验研究,测定LED光学样机在大气环境中以及在热真空环境中的温升及硅光电池电流变化情况,并分析其结点温度与光强的对应关系,得出LED的输出光效随着结点温度的升高而降低的结论。分析比较了在大气、热真空环境条件下的光效输出随结点温度变化的异同,验证了在大气中比在真空环境中光效下降较慢。     

Improvement of color-rendering characteristics of white light emitting diodes by using red quantum dot films

Red quantum dot (QD) films were applied to a conventional white light-emitting-diodes (LEDs) module consisting of 72 LEDs for improving color-rendering properties. Total three QD films with different QD concentrations, two diffuser plates, and six optical configurations were combined and investigated to find an optimized optical structure. QD films formed a red peak near 630 nm in the spectrum which significantly increased the overall color rendering index (CRI). The lateral optical cavity formed by a vertical QD wall and the vertical cavity formed by the diffuser plate and the reflection film in the lighting module played an important role in the improvement of the color-rendering properties. Especially, the adoption of the lateral optical cavity formed by the QD wall was an effective way to improve both efficiency and color rendering properties of the LED lighting. The present result suggests a new possibility of designing high-CRI LED light sources whose color properties can be tuned easily by simply applying and relocating QD components in conventional LED lightings.     

基于氧化锌纳米线的紫外发光二极管

构建了基于n-ZnO纳米线/p-Si异质结的紫外发光二极管.ZnO纳米线准阵列采用水热法生长于重掺p型Si片上.此法简易，反应温度低，易于大规模生产；其产物ZnO纳米线结晶良好，以c轴为优势取向，光激发下的紫外荧光发射很强.二极管的电学接触采用聚合物填充的In阴极或以氧化铟锡(ITO)玻璃紧压形成阴极.它们的I-V特性体现出良好的二极管性质.在正向偏置电压驱动下，构建的发光二极管可稳定发射波长在387nm的较强的近紫外光和较弱的绿光. 关键词： ZnO纳米线 异质结 电致发光 水热法     

带介质分布式Bragg反射镜结构高性能共振腔发光二极管的研究

采用等离子体增强化学气相沉积高低频交替生长法生长了SiO₂/Si₃N₄透明介质分布式Bragg反射镜(DDBR), 提出了对DDBR采用干、湿法并用的腐蚀方法. 采用传输矩阵法理论分析了DDBR, 得出了为满足出光增益要求的反射率和DDBR结构. 使用光致发光(PL)谱仪测量分析了DDBR反射谱和光致发光谱, 获得了使光致发光谱辐射增强的DDBR结构, 在整个光致发光谱380–780 nm波段, 整体辐射增强1.058倍, 在谐振波长处辐射增强1.5倍, 半峰全宽值由23 nm变窄为10.5 nm, 获得了很好的光谱纯度. 利用最优DDBR结构制成了高性能共振腔发光二极管器件, 与普通结构相比, 实现了低开启电压1.78 V; 在20 mA注入电流下, 轴向光强提高了20%, 光功率和光效分别提高了27.7%和26.8%, 光功率衰减缓慢; 在0–100 mA注入电流下, 没有明显的下降趋势, 表现出了良好的温度稳定性. 关键词： 发光二极管 共振腔 介质分布式布拉格反射镜 辐射增强     

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.     

Multi-objective design and extended optimization for developing a miniature light emitting diode pocket-sized projection display

This research proposes a new extended optimization method for a miniature light emitting diode (LED) pocket-sized projection display, introducing integration of the Taguchi method and principal component analysis in order to optimize the multiple quality characteristics of an LED pocket-sized projection display. With the aid of interactive optimization, control factors with three different levels are carefully selected in the complicated preliminary experiments. A set of optimal design parameters is well selected for best results on the combined effects of the total luminous flux, illumination uniformity, and the packing size of the system. The selected control factors are inclusive of major lens and system specifications, such as lens overall length, X-CUB semi-aperture, length of light integrator, width of integrator, total internal reflection (TIR) prism entering semi-diameter for the TIR prism, air-gap of the TIR prism, and digital micromirror device (DMD) position; an L18 orthogonal array is applied and implemented in the experiments. According to experimental results, the optimal design parameters for the projection display can be determined as A1 (lens specifications: type I), B3 (lens length: overall length), C1 (X-CUB semi-aperture: 8 mm), D3 (integrator length: 36.6 mm), E2 (integrator width: 3.5 mm), F2 (TIR prism entering semi-diameter: 11 mm), G1 (TIR prism air-gap: 1.0024 mm), and H1 (DMD location: −0:5 mm). In addition, analysis of variance (ANOVA) is also employed to identify the factor A (lens specifications), factor D (integrator length), factor F (TIR prism entering semi-diameter), and factor G (TIR prism air-gap) as key parameters, which account for 71.82% of the total variance. The other factors when compared are found to have relatively weaker impacts on the process design. Furthermore, a confirmation experiment of the optimal design parameters shows that the aforesaid multiple performance characteristics are optimized to achieve the best levels. It is concluded that Taguchi method and principal component analysis (PCA) combine to optimize and then minimize the LED pocket-sized projection display system, which not only yields a sufficient understanding of the effects of control factors, but also produces an optimized design to ensure that the LED pocket-sized projection display system exhibits the best multiple performance characteristics.     

微腔效应对顶发射串联蓝光有机电致发光器件性能的影响

相比于传统有机电致发光器件,串联有机电致发光器件的发光效率与寿命均得到明显提升.因此,深入研究微腔效应对顶发射串联有机电致发光器件性能的影响具有重要意义.本文以蓝光器件为例,通过光学仿真模拟与实际实验相结合的方法,研究了顶发射串联蓝光器件的光学性能与电学性能变化规律.具体实验为:分别制备了顶发射串联蓝光器件,使其两个发光层位置分别位于器件光学结构中的第一与第二反节点、第二与第三反节点、第三与第四反节点.分析并确定了顶发射串联蓝光器件的两个发光层位置分别位于第二反节点与第三反节点处时,器件性能较佳.即:当器件电流密度为15 mA/cm^2时,器件电流效率为10.68 cd/A(色坐标CIEx,y=0.14,0.05),其亮度衰减到95%所需时间为1091.55 h.可能原因是:器件腔长较长时,既可以改善第一发光单元的空穴与电子平衡度、削弱表面等离激元效应,降低膜厚波动性对器件腔长的影响性;又可以在一定程度内起到包裹Partical的作用,提高效率,延长寿命.这一研究成果为设计高效率、长寿命的顶发射串联器件提供了重要依据.     

Light extraction efficiency enhancement in organic light emitting diodes based on optimized multilayer structures

The main focus of this study is to improve the light extraction efficiency, as well as directionality of organic light emitting diodes (OLEDs) using multi-layer structures between Indium tin Oxide (ITO) and glass layers in a typical OLED. In conventional OLEDs, only about half of the light generated in the emission zone can reach to the glass substrate due to refractive index mismatch in ITO (n = 1.8?i0.01)/glass (n = 1.51) interface. The main attempt is to reduce the share of total internal reflection (TIR) and hence, the effect of different structures such as Thue-Morse and Fibonacci have been investigated and optimized with suitable layer thickness and materials based on Transfer Matrix Method (TMM). The most effective Multi-layer structures have been added to conventional OLED and have been analyzed the extraction efficiency using Finite Difference Time Domain (FDTD) method. Results show large enhancement of extraction efficiency (about 40%) in ITO/glass interface. Using this idea and applying micro-lenses array to glass substrate at the same time, one can get even higher extraction efficiency in OLED. The interesting aspect of this project is its easy fabrication process in order to commercialize the product with highest extraction efficiency and low fabrication cost.