AlGaInP LED出光效率的模拟

采用有限元法来模拟研究采用透明电极AlGaInP LED出光效率的影响因素和分布情况,并在此基础上对不透明电极进行优化以提高芯片的出光效率。研究发现,随着窗口层厚度的增加,顶面出光效率有所下降,侧面出光效率大大提高,总出光效率呈上升趋势,且总出光效率的最高分布区从芯片的四个直角区域向中央圆形电极边缘靠近。然而,随着芯片尺寸的增加,其变化趋势正好与之相反。在此基础上进一步对普通生产芯片进行模拟分析,得知其光提取效率最高区主要分布在芯片的四个直角区域,并以此为指导进行不透明电极形状的优化,进而对其条形电极的宽度进行优化,可使所获得的出光效率比传统圆形电极提高了62.85％,能够为实际生产提供一定的理论指导。     

电极形状对GaN基发光二极管芯片性能的影响

采用Crosslight APSYS这一行业专业软件对p-GaN,InGaN/InGaN多量子阱,n-GaN和蓝宝石的芯片结构研究了不同电极形状与器件的光电性能之间的关系.优化设计了普通指形电极、对称型指形电极、h形指形电极、旋转形电极、中心环绕形电极、树形电极等6种电极结构.通过电极优化设计,电流分布更加均匀,减小了电流的聚集效应.优化后的电极结构结果表明:芯片的电特性得到了提高,芯片的光特性得到了明显改善,芯片的出光效率大幅度提高,芯片的转化效率得到了提升.     

功率型GaN基发光二极管芯片表面温度及亮度分布的物理特性研究

基于电流连续方程、欧姆定律及定性三维热流传导模型研究发光二极管(LED)芯片 的电流密度分布、热量、温度之间的相互交叉关系,进而测试分析GaN基蓝光 LED电流扩展效应和亮度分布的关系,认为芯片亮度变化趋势可作为判别电流扩 展性能的有效手段. 由于芯片表面温度、亮度分布和电流密度之间存在紧密的联结 关系,通过测试芯片表面温度或亮度分布就可定性了解器件电流扩展性能, 从而为优化电极结构提供一种判定依据. 在不同电流和热沉温度下,进一步 讨论了电流密度非均匀性和亮度分布的关系, 电流密度拥挤将导致芯片局 部区域热量堆积,非辐射复合作用增强,限制出射光子数目, 因此热 量是影响亮度分布的重要因素之一. 通过载流子传输机理进一步说明 温度影响亮度均匀性的原因,并通过实验说明理论分析的可行性. 通过优化电极结构能改善器件的电流扩展效应以及亮度均匀性, 对提高大功率LED的可靠性具有重要作用.     

电极结构对AlGaInP-LED阵列电流分布的影响

以AlGaInP-LED外延片为基片,设计了分辨率为320×240、像素尺寸为100 μm×100 μm的微型LED阵列。针对目前LED阵列普遍存在的电流分布不均匀的问题,建立了内部电流分布模型,研究了电极结构、电极尺寸及电极间距等不同因素对LED电流分布造成的影响。在单条形电极结构的基础上进行优化,综合考虑不透明电极的遮光效应等因素得到三条形电极结构为最优的电极结构,该电极结构的LED有源层均匀发光面积比未经优化的单条形电极提高了65.02%,比双条形电极提高25.63%,有效提高了微型LED阵列的出光效率,对改善LED芯片发光均匀性具有参考意义。     

影响倒装焊LED芯片电流分布均匀性的因素分析

为研究影响倒装LED芯片电流密度均匀分布的因素, 建立了芯片的三维有限元电学模型, 采用COMSOL有限元仿真方法, 分析了芯片尺寸、电极结构、电流注入点对倒装LED芯片电流分布均匀性的影响, 并对相关机理进行了探讨. 研究结果表明, 芯片尺寸的增加扩展了电流的横向传输路径与横向电阻, 使LED芯片电流分布的不均匀性呈指数型恶化; 叉指式电极结构可有效缩短电流传输途径, 增加叉指电极数目有利于电流均匀性的提高; 通过在块状电极上合理设计电流注入点可缩短电流传输路径, 显著提高电流的均匀性.     

不同形状的电流阻挡层对GaN基LED光效的影响

电流阻挡层(CBL)可以改善发光二极管(LED)的发光效率和输出光功率,其形状对电流的阻挡作用有影响。本文通过等离子体增强化学气相沉积设备(PECVD)在InGaN/GaN多量子阱外延片上制备了SiO2薄膜,并腐蚀出不同结构作为电流阻挡层:A组形状与P电极形状相同,B组为Y形CBL,C组为点状CBL。通过对这3组芯片与常规芯片的对比,发现加入CBL对小功率LED的电压特性影响比较小,并且电流阻挡层形状与金属电极形状相同时对光效的提高最大,可以提高14.6%。     

大功率倒装LED芯片陶瓷封装器件顶面微区发光均匀性

高功率密度的陶瓷封装LED器件在大电流工作时,其顶面发光均匀性是该类器件的关键指标。本文在3.5 mm×3.5 mm的氮化铝陶瓷基板上金锡共晶了1.905 mm×1.830 mm(75 mil×72 mil)的LED倒装蓝光大功率芯片,然后分别制作成蓝光器件和白光器件,并分别对器件顶面的微区发光均匀性进行了研究。结果表明,蓝光器件在电流3 A时,其顶面光强分布均匀,均匀性受N电极孔和电极间隙的影响较小;在4～8 A电流时,蓝光器件顶面光强分布不均匀,贯穿N电极孔测试区的光强大于电极孔之间测试区的光强,电极间隙区光强最低,离N电极孔越远的测试点光强越低;蓝光器件在8 A时整体光强达到饱和,而不同微区的光饱和程度及峰值波长随电流的变化有所不同;白光器件在0～4 A电流时,其顶面光强分布均匀。     

大功率GaN基发光二极管的电流扩展效应及电极结构优化研究

定性分析了GaN基LED的电流扩展效应,发现电流密度和电流横向扩展的有效长度对电流均匀扩展有很大影响.基于此,对GaN基大功率LED提出了优化的电极结构,以减缓电流拥挤效应,降低器件串联电阻.通过用红外热像仪测量器件表面的温度分布,发现具有优化的环形插指电极结构的GaN基大功率LED表面温度分布比较均匀,证明芯片接触处电流扩展均匀,局部电流密度降低,减小了焦耳热的产生,增强了器件的可靠性. 关键词： 氮化镓 发光二极管 电流扩展 电极结构优化     

AlGaInP大功率发光二极管发光效率与结温的关系

目前,AlGaInP大功率发光二极管(LED)存在的主要问题是大电流工作时发热严重,主要是由于电流扩展不均匀、出光面电极对光子的阻挡和吸收以及器件材料与空气折射率之间的差距引起的全反射现象,这些因素造成大功率LED出光受到限制、发光效率低、亮度不高.提出了一种复合电流扩展层和复合分布式布拉格反射层(DBR)的新型结构LED,使得注入电流在有源区充分地扩散,同时提高了常规单DBR对光子的反射率.结果显示,这种新型结构LED比常规结构LED的性能得到了很大的提升,350 mA注入电流下两者的输出光功率分别为4 关键词： 复合电流扩展层 复合分布式布拉格反射层 出光效率 结温     

电流阻挡层对大功率LED光电热特性的影响

LED芯片作为LED光源的核心,其质量直接决定了器件的性能、寿命等,因此在内量子效率已达到高水平的情况下,致力于提高光提取效率是推动LED芯片技术发展的关键一步。由于蓝宝石衬底具有绝缘特性,传统LED将N和P电极做在芯片出光面的同一侧,而芯片出光面上的P电极焊盘金属会遮挡吸收其正下方发光区发出的大部分光而造成光损失,为改善这一现象并缓解P电极周围的电流拥挤效应,本文设计制备了在P电极正下方的氧化铟锡(ITO)透明导电层和p-GaN之间插入SiO_2薄膜作为电流阻挡层(CBL)的大功率LED,并与无CBL结构的大功率LED相比较。对未封装的有无CBL结构的LED在350 mA电流下进行正向偏压,辐射通量,主波长等裸芯性能测试,结果显示两种芯片的正向偏压均集中在3～3.1 V,而有CBL结构的LED光输出功率有明显提升,这是因为CBL阻挡了电流在P电极正下方的扩散,减少流向有源区的电流密度,故减小了P电极对光的吸收和遮挡,且电流通过CBL引导至远离P电极的区域,缓解了电极周围的电流拥挤。对两种芯片进行相同结构和工艺条件的封装,并对封装样品进行热特性及10～600 mA的变电流光电特性测试,得到两种器件的发光光谱及光功率等光学特性。结果表明随着电流增加,两种器件的光谱曲线均发生蓝移,且有CBL结构的LED主波长偏移量较无CBL结构LED少10 nm,可见有CBL结构的LED光谱受驱动电流变化的影响更小,因此其显色性能更为稳定。而在小电流条件下, CBL对器件光功率的影响不大,随着工作电流的增大, CBL对器件光功率的改善效果逐渐提升。在大电流条件下,无CBL结构的LED结温更高,正向电压更低,随电流的增大二者之间的电压差增大。在25℃的环境温度, 350 mA工作电流下,加入CBL结构使器件电压升高约0.04 V,但器件光功率最高提升了9.96%,且热阻明显小于无CBL结构器件,说明有CBL结构LED产热更少。因此CBL结构大大提高了器件的光提取效率,并使其光谱漂移更小,显色性能更为稳定。     

Improvement of performance characteristics of deep violet InGaN DQW lasers using a strip DQW active region

The effect of the laser ridge width on the performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) has been numerically investigated. Simulation results indicated that threshold current of LDs is decreased and slope efficiency and differential quantum efficiency (DQE) are increased by decreasing ridge width, whereas output power is decreased. The results also showed that a decrease of more than 1 μm in the ridge width reduces the threshold current, whereas the slope efficiency, output power, and DQE are decreased. A new DQW LD structure with a strip active region has been proposed to obtain a lower current threshold and higher output power, slope efficiency, and DQE. The results showed the InGaN DQW LD with a strip DQW active region has the highest output power, slope efficiency, and DQE; it also has a lower threshold current compared with that of the original LD. The comparative study conducted for the LDs with output emission wavelengths of 390, 414 and 436 nm has also confirmed the enhancement in LD performance using the strip DQW active region structure.     

An optimum design and fabrication of lens on luminous uniformity and light extraction of high-power light-emitting diode

The effect of lens inner structure on radiation pattern and light extraction efficiency of light-emitting diode (LED) and the application to artificial light in compact greenhouse is demonstrated. A commercial software package of Trace Pro and one-factor at-a-time (OFAT) method are used to simulate the lens with different inner structure. The optimum parameters of lens inner structure design for the maximum light extraction efficiency and the best uniform luminous are described by the corner radius of curvature, lens width, and lens height, respectively. For a real single LED module, base on the optimum parameters of lens inner structure, the corresponding best luminous uniformity is 62% and corresponding output extraction is 14.11 lm. The maximum uniformity of illumination for LED matrix assembled by LED modules with optimum lens is 88% and corresponding light extraction 1141 lm. In comparison with a commercial artificial light of LED matrix used in agriculture, the high-power LED module with proposed lens inner structure exhibit good improvement in uniformity of illumination and light extraction. This study may provide a practical guideline for design and fabrication of a high-performance lens used in various compact agricultural applications.     

Tuning a nano-pillar array for enhancing the photoluminescence extraction efficiency of GaN-based light-emitting diodes

We demonstrate the fabrication of hexagonal nano-pillar arrays at the surface of GaN-based light-emitting diodes (LEDs) by nanosphere lithography. By varying the oxygen plasma etching time, we could tune the size and shape of the pillar. The nano-pillar has a truncated cone shape. The nano-pillar array serves as a gradual effective refractive index matcher, which reduces the reflection and increases light cone. It is found that the patterned surface absorbs more pumping light. To compare extraction efficiencies of LEDs, it is necessary to normalize the photoluminescence power spectrum with total absorption rate under fixed pumping power, then we could obtain the correct enhancement factor of the photoluminescence extraction efficiency and optimized structure. The highest enhancement factor of the extraction efficiency is 10.6.     

条形几何尺寸对光通信用GaAs-GaAlAs边发光管性能的影响

本文阐述了条形几何尺寸对GaAs-GaAlAs边发光管性能的影响.计算了不同条宽的侧向电流分布和光场分布情况.计算与实验结果很好相符.通过合理的折衷,在100mA的低注入电流下获得了性能良好的边发光二极管,其标准尾纤的输出功率大于100μW,光带宽超过120MHz.是三次群光通信较为理想的光源器件.     

Analysis of optical coupling between air-holes photonic crystal and tapered dielectric waveguides

Two types of structures for the optical coupling between photonic crystal waveguide (PCW) with triangular air-holes lattice and tapered dielectric waveguide (TDW) are investigated. The TDWs are coupled with PCW at the input and output connections of the PCW, which can constitute a unidirectional waveguide structure. The transmission efficiencies of the input and output coupling are analyzed theoretically for different coupling structures. It is found that the coupling efficiencies vary with the width and length of coupling region. When the light transmitted from TDW to PCW, the highest transmission efficiency is 92.6%, and it is 99.6% when the light transmitted from PCW to TDW. Then the total transmission efficiency of the entire waveguide is simulated and it can reach 92.3% for one type of structure and is a little lower for the other type of structure under the chosen optimal structure parameters. Considering the current processing accuracy, the structure mentioned above should be an effective coupling manner that can be easily realized.     

Optimization of Extraction System for Cold Cathode Ion Source

We have simulated ion trajectories with the SIMION 3D, version 7.0, package to optimize the extraction system of a cold-cathode ion source and compared the results with experimental data collected under the same operational conditions. The simulation determined the negative voltage applied to the extractor electrode and the extraction gap widths that maximize the ion-beam current for singly charged nitrogen ions with low emittance and small diameter. The experiment measured the input electrical discharge and output ion beam characteristics of the source at different nitrogen pressures. The extractor electrode voltage and the extraction gap width were determined at 8?×?10^?4?Torr nitrogen. The results of the simulation agreed well with the experimental data.     

提高OLED光导出效率的异形金属光栅的设计与优化

提出一种用于有机电致发光器件(OLED)的双面对称矩形金属光栅电极,采用时域有限差分方法(FDTD)模拟研究了OLED中表面等离子体激元的激发和耦合传输的物理规律和物理机制,详细计算和分析了该光栅结构的周期、槽宽、光栅高度、槽底厚度、入射光的入射角与电极透射效率的关系,并由此优化了结构的几何参数,使金属电极的光导出效率相对于通常的金属银层电极增强了1.77倍,为基于表面等离子体激元的高效光导出器件的优化设计提供了理论依据。     

Reduction of light signal pulse distortion in cascaded sum-frequency-generation and difference-frequency-generation wavelength conversion

Cascaded sum-frequency-generation (SFG) and difference-frequency-generation (DFG) can implement a wavelength conversion between arbitrary combinations of input and output signal wavelengths. By using a tunable wavelength pump light, the output wavelength can be tuned to a desired wavelength. As in many wavelength conversion devices using the nonlinear optical effect, the group velocity difference between light pulses with different wavelength causes a walk-off effect deforming the output pulse shape. Thus the device length should be kept short to avoid the walk-off effect resulting in limited conversion efficiency. In this report, we propose a method for a quasi-phase matched (QPM) device to maintain the pulse shape of the SFG light pulse along the propagation distance. The output DFG light pulse deformation is suppressed and the conversion efficiency can be increased by extending the device length.