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.     

两种谐振腔长度的微腔有机电致发光器件模拟

微腔的谐振腔长度直接影响微腔有机电致发光器件(MOLED)的发光特性,根据微腔器件的相关计算公式运用传输矩阵法,分别对微腔长度L=λ/2和L=λ(λ:中心波长)时,在微腔内不同位置激子复合发光的电致发光谱(EL)进行模拟计算和比较。发现:微腔长度为L=λ/2时,峰值均为520nm,半峰全宽均为17nm,激子处在微腔的中心位置时,峰值强度和积分强度均为最大。L=λ时,激子在腔内不同位置时,峰值均为520nm,半峰全宽均12nm,在腔的中心区域时,与L=λ/2时正好相反,峰值强度和积分强度最小。分析后判断是因为两种长度的微腔内电场强度分布不同,激子位于腔内电场的最大值处发光性能最好。说明要制作出高效率的MOLED,要区别不同谐振腔长度,并使激子处于腔内电场最大处。     

发光二极管灯具鳍片式散热结构

为了提高发光二极管（LED）灯具的性能,依据LED散热指标,计算了散热面积,建立了LED鳍片式散热模型,最终利用ANSYS软件对其进行了仿真。研究结果表明:当鳍片间距与鳍片厚度比为3∶2、底座厚度与鳍片厚度为1∶1时,散热效果最好;随着鳍片数目和鳍片高度的增加,散热效果也有所增强。     

发光二极管灯具鳍片式散热结构

为了提高发光二极管（LED）灯具的性能,依据LED散热指标,计算了散热面积,建立了LED鳍片式散热模型,最终利用ANSYS软件对其进行了仿真。研究结果表明：当鳍片间距与鳍片厚度比为3∶2、底座厚度与鳍片厚度为1∶1时,散热效果最好;随着鳍片数目和鳍片高度的增加,散热效果也有所增强。     

Surface and edge emission in organic light emitting devices

We report the studies on photoluminescence (PL) and electroluminescence (EL) spectra of organic light emitting diodes (OLED) based on most widely used light emitting material, i.e., Tris-(8-hydroxyquinoline) aluminum (Alq₃). PL studies from the edges and top surface were carried out on different thicknesses of single layer of Alq₃ coated on glass substrate and the PL intensity from the edges was found to be more than that from the top surface. On the other hand EL emission intensity from the surface was found to be larger than that from the edges of the OLED device. The discrepancy in the PL and EL emission from edge and the top surfaces is discussed. The effect of the thickness of Alq₃ layer on the PL intensity and the emission spectra are also investigated.     

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.     

光子晶体发光二极管

利用光子晶体的光子禁带和光栅衍射效应可以提高LED的出光效率,扩大LED的应用范围。总结了光子晶体发光二极管的原理和典型器件。通过比较表明,与光子禁带效应相比,利用光栅衍射效应提高LED出光效率的方法更适用于电注入发光。因此可望用更廉价的方法在LED表面制造光子晶体,可通过光栅衍射效应来有效地提高其出光效率。     

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.     

3,4,9,10-Perylenetetracarboxylicdiimide as an interlayer for ultraviolet organic light emitting diodes

Ultraviolet organic light emitting diodes with 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI) interlayer have been achieved. The emission spectrum and intensity were strongly dependent on the thickness of PTCDI interlayer, in spite of the fact that PTCDI has neither much lower HOMO nor much higher LUMO level, which is considered necessary for efficient charge blocking layers. The influence of PTCDI layer was investigated in three different device configurations and obtained results are discussed. For optimal device configuration, OLED with emission centered at 370 nm and turn-on voltage of 4.5 V is obtained.     

Pure blue emission from undoped organic light emitting diode based on anthracene derivative

This paper presents organic light emitting diodes (OLEDs) which were fabricated by using undoped 9,10-di(2-naphthyl)anthracene (ADN) as the emitting layer, N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-amine (TPD) as the hole transporting layer, and one of tris-(8-hydroxy-quinolinato) aluminum (Alq₃), 4,7-diphenyl-1,10-phenanthroline (Bphen) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as the electron transporting layer. By optimization for the thickness of device, efficient pure blue organic light emitting diodes were obtained, which is attributed to the synergy of both the hole transporting layer and the electron transporting layer.     

The effect of ITO films thickness on the properties of flexible organic light emitting diode

Indium tin oxide (ITO) thin films were deposited on cyclic olefin copolymer substrate at room temperature by an inverse target sputtering system. The crystal structure and the surface morphology of the deposited ITO films were examined by X-ray diffraction and atomic force microscopy, separately. The electrical properties of the conductive films were explored by four-point probing. Visible spectrometer was used to measure the optical properties of ITO-coated films. The performance of the flexible organic light emitting diode device with different thickness anode was investigated in this study.     

基于缺陷光子晶体结构的GaN基发光二极管光提取效率的有关研究

现有的研究表明,利用光子晶体可以有效提高发光二极管的光提取效率.由于在制造时光子晶体中可能会存在缺陷和错位,本文基于时域有限差分法对光子晶体中的缺陷和错位对发光二极管发光效率的影响进行了研究.数值仿真结果表明,光子晶体中少量缺陷或者微小错位并不会降低发光二极管的光提取效率,其中某些缺陷反而能增强光子晶体发光二极管的光提取效率.本文对其物理机理给出了详细的理论分析,并设计了一种具有缺陷的光于晶体,在未刻蚀到有源层(离有源层20 nm)的情况下,其光提取效率达到了完美光子晶体的1.6倍.通过对这种缺陷光子晶体的空间频谱分析可知,可以通过设计具有特殊空间频谱分布的光子晶体来提高发光二极管的发光效率,这对设计高光提取效率的光子晶体结构和制造高效率的发光二极管有指导意义.     

Influence of cavity de-tuning in semiconductor microcavity LEDs

Data are presented showing the precise role of the cavity de-tuning on the emission properties of semiconductor microcavity light emitting diodes (MC-LEDs). Enhanced output power and narrow line width emission have been observed over a wide range of cavity de-tunings, with a power reduction of less than −1 dB observed for ±12 nm de-tuned devices. For a resonantly de-tuned MC-LED, the slope efficiency extracted from the power output versus current characteristics decreases monotonically with increasing temperature. However, for a MC-LED de-tuned +5.6 nm to long wavelength with respect to the room temperature quantum well (QW) peak, the extracted slope efficiencies vary by less than ±0.5 dB over a temperature range of greater than 65°C. Compared to a conventional LED, narrower beam divergence is observed for MC-LEDs de-tuned to short wavelength with respect to the bare QW peak. For positively de-tuned MC-LEDs the beam divergence broadens, and the far-field emission profiles exhibit a double-lobed pattern that is sensitive to pump level.     

New double graded structure for enhanced performance in white organic light emitting diode

This study presents a new design that uses a combination of a graded hole transport layer (GH) structure and a gradually doped emissive layer (GE) structure as a double graded (DG) structure to improve the electrical and optical performance of white organic light-emitting diodes (WOLEDs). The proposed structure is ITO/m-MTDATA (15 nm)/NPB (15 nm)/NPB: 25% BAlq (15 nm)/NPB: 50% BAlq (15 nm)/BAlq: 0.5% Rubrene (10 nm)/BAlq: 1% Rubrene (10 nm)/BAlq: 1.5% Rubrene (10 nm)/Alq₃ (20 nm)/LiF (0.5 nm)/Al (200 nm). (m-MTDATA: 4,4′,4″ -tris(3-methylphenylphenylamino)triphenylamine; NPB: N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-(1,1′-biphenyl)-4,4′-diamine; BAlq: aluminum (III) bis(2-methyl-8-quinolinato) 4-phenylphenolate; Rubrene: 5,6,11,12-tetraphenylnaphthacene; Alq₃: tris-(8-hydroxyquinoline) aluminum). By using this structure, the best performance of the WOLED is obtained at a luminous efficiency at 11.8 cd/A and the turn-on voltage of 100 cd/m² at 4.6 V. The DG structure can eliminate the discrete interface, and degrade surplus holes, the electron-hole pairs are efficiently injected and balanced recombination in the emissive layer, thus the spectra are unchanged under various drive currents and quenching effects can be significantly suppressed. Those advantages can enhance efficiency and are immune to drive current density variations.     

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。     

Improved outcoupling of light in organic light emitting devices, utilizing a holographic DFB-structure

In this work organic light emitting devices (OLEDs) were fabricated implementing gratings, in order to extract waveguided electroluminescence (EL). The gratings were recorded by exposing thin films of the molecular azo glass N, N′-bis (4-phenyl)-N, N′-bis [(4-phenylazo)-phenyl] benzidine (AZOPD) to holographic light patterns. The photopatterned AZOPD serves as hole transport material for devices with aluminum-tris(8-hydroxyquinoline) doped with 1% of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (Alq₃:DCM) as emissive/electron transport layer. The corrugated devices showed enhanced emission in the forward direction. The emitted light is polarized preferably parallel to the grating lines. In addition, we have found a doubling in the total luminance with respect to the unstructured device.     

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     

The luminescence properties of Er-doped and Er-Tm-co-doped phosphate glasses for white light emitting diode

Phosphate glasses and glass ceramics doped with Er³⁺ and co-doped with Er³⁺-Tm³⁺ are presented in this work. The luminescence properties have been characterized by absorption, excitation and emission spectra. All samples excited by blue light could emit a combination of blue/green/orange/red wavelength giving white light. For Er³⁺-doped glasses, a self-quenching effect has been obtained and an adjustable tune comes out after crystallization. For co-doped glasses, the red emission at 651 nm has been enhanced due to the existence of Tm³⁺, which could be relative to both the overlapped emissions and the energy transfer from Tm³⁺ to Er³⁺.     

基于电容和电导特性分析GaN蓝光发光二极管老化机理

采用正向交流小信号方法测试和分析老化前后GaN发光二极管（LED）的电容-电压特性,结合串联电阻、理想因子、隧穿电流参数讨论负电容以及电导变化情况.基于L-V曲线定性分析老化前后负电容的阈值电压,老化之后样管的受主浓度降低,辐射复合概率下降,大量缺陷以及非辐射复合中心出现,对载流子俘获作用增强,造成负电容降低.反向偏压以及小正向偏压下,隧穿效应导致老化之后样管的电导增大;正向偏压大于2.2 V区域,考虑串联电阻效应,老化后样管电导减小.在分析LED电容-电压、光输出、电学特性曲线与老化机理基础上,通过实验论证以及理论解释表明,负电容以及电导特性可作为分析LED老化特性的参考依据. 关键词： GaN发光二极管 负电容 电导 老化机理     

可调色红光有机电致发光器件

介绍了具有可调节发光光谱的高效红光有机发光二极管(OLED)器件,利用具有高三重态能量的9.9-螺二芴二苯基氧化磷(SPPO1)作为发光层的主体材料及空穴阻挡层,二(1-苯基异喹啉)(乙酰丙酮)合铱(III) (Ir(piq)2(acac))作为客体发光材料,在发光层内SPPO1的能量分别由福斯特和迪克斯特传递到Ir(piq)2(acac)的单重态和三重态从而发出红色磷光,通过调节磷光客体材料的比例得到最优器件结构,从而得到具有较好发光效率和发光亮度并可调节色纯的有机发光二极管器件。