有机磷光电致发光器件中的复合宽度和外量子效率

从经验公式出发,基于T-T湮灭过程,建立了有机磷光电致发光器件中复合宽度和外量子效率的理论模型.结果表明:(1)随外加电压升高,器件的复合宽度减小,外量子效率增加;(2)随器件厚度的增加,复合宽度相应增加,但外量子效率在不同的电压下呈现不同的变化趋势;(3)外量子效率随复合电流密度的增大而显著降低.讨论了外加电压和器件厚度对复合宽度的影响,分析了外量子效率随外加电压、器件厚度及复合电流密度变化的原因.     

有机电致发光器件中复合发光的电场和温度关系

通过分析有机电致发光器件中载流子注入、输运、激子的解离与复合过程，提出了激子解离与复合的理论模型。基于电流连续性方程和Poisson方程，给出了激子复合几率、电流密度及复合效率表达式。研究了外加电压和温度对器件中激子的复合几率及在各种接触条件下外加电压对器件电流和复合效率的影响。结果表明：(1)在一个较宽的注入势垒范围内，复合几率随电场和温度的升高而降低；(2)固定阴极势垒，而阳极势垒由小变大时，器件电流由接触限制向空间电荷限制转变；(3)复合效率随外加电压升高先增加，当电压达一临界值时而陡降，并存在一个最佳的注入势垒值。其计算值与所报道的实验结果相符合。     

壳层厚度对于量子点/聚合物复合电子存储器件性能的影响

研究了一种含有不同壳层结构量子点的聚乙烯咔唑(PVK)/Cd Se量子点复合体系电双稳器件,结果发现基于无壳层量子点的器件电荷存储能力较差,随着壳层厚度的增加,器件的电学特性由双稳态向三稳态转变。通过电容-电压(C-V)的测试结果表明,壳层的厚度对于量子点的电荷捕获能力有重要的影响,从而导致器件表现出不同的存储特性。     

利用PtOEP掺杂改善Spiro发光器件的发光效率

为了利用有机三线态发光提高有机发光器件的发光效率,用磷光材料掺杂到聚合物主体中作为发光层,制备有机电致发光器件.在测量器件的电流-电压特性、发光亮度-电压特性和电致发光谱的基础上,计算了器件的外量子效率,研究了磷光材料的掺杂浓度对器件发光效率的影响.结果表明,对特定的材料体系,适当控制掺杂浓度,可以同时观察到荧光和磷光光谱,使掺杂器件的外量子效率在纯聚合物发光器件的基础上得到明显提高.     

双层有机电致发光器件有机层厚度优化的数值研究

在陷阱电荷限制电流传导理论的基础上,提出了双层有机电致发光器件的数值模型,研究了结构为“阳极/空穴输运层( HTL) /发光层( EML) /阴极”的器件中电流密度和量子效率随有机层的特征陷阱能量、陷阱密度和载流子迁移率的依赖关系.研究发现,对于给定的HTL 和EML 的特征陷阱能量、陷阱密度和载流子迁移率,存在一个最优的HTL 和EML 之间的厚度比率,在此最优厚度比下,器件的电流密度和量子效率达到最大.通过有机层厚度的优化,器件的电流密度和量子效率可提高多达两个数量级.另外,还研究了最优厚度比随有机层特征陷阱能量、总陷阱密度和载流子迁移率之间的     

双层有机电致发光器件有机层厚度优化的数值研究

在陷阱电荷限制电流传导理论的基础上,提出了双层有机电致发光器件的数值模型,研究了结构为"阳极/空穴输运层(HTL)/发光层(EML)/阴极"的器件中电流密度和量子效率随有机层的特征陷阱能量、陷阱密度和载流子迁移率的依赖关系. 研究发现,对于给定的HTL和EML的特征陷阱能量、陷阱密度和载流子迁移率,存在一个最优的HTL和EML之间的厚度比率,在此最优厚度比下,器件的电流密度和量子效率达到最大.通过有机层厚度的优化,器件的电流密度和量子效率可提高多达两个数量级.另外,还研究了最优厚度比随有机层特征陷阱能量、总陷阱密度和载流子迁移率之间的定量关系.     

高亮度发光二极管外量子效率的计算

本文对典型结构高亮度发光二极管（ＨＢ－ＬＥＤ）的注入电流扩展以及器件的光输出进行了详细的理论分析，结果表明具有较厚顶层的器件容易实现注入电流的扩展，而具有较厚的底层即具有透明衬底的器件容易实现光耦合输出，因此引入较厚顶层和底层是提高ＬＥＤ的外量子效率的有效手段．最后分别计算出不同顶层厚度下具有吸收衬底和透明衬底的ＬＥＤ的外量子效率，这两类ＬＥＤ 最大外量子效率分别为 １２．０５％和２０．１２％．     

利用PtOEP掺杂改善Spiro发光器件的发光效率

为了利用有机三线态发光提高有机发光器件的发光效率,用磷光材料掺杂到聚合物主体中作为发光层,制备有机电致发光器件.在测量器件的电流-电压特性、发光亮度-电压特性和电致发光谱的基础上,计算了器件的外量子效率,研究了磷光材料的掺杂浓度对器件发光效率的影响.结果表明,对特定的材料体系,适当控制掺杂浓度,可以同时观察到荧光和磷光光谱,使掺杂器件的外量子效率在纯聚合物发光器件的基础上得到明显提高.     

白光有机电致发光器件发光稳定性研究

基于红绿/蓝双发光层,制作了结构为ITO/MoO ₃(10nm)/NPB(40nm)/TCTA(10nm)/CBP:R-4B(2%):GIR1(14%,X nm)/mCP:Firpic(8%,Y nm/BCP(10nm)/Alq₃(40nm)/LiF(1nm)/Al( 100nm)的白色全磷光有机电致发光器件(OLED),通过 调节红绿发光层的厚度X与蓝光发光层的厚度Y,研究了不同发光层厚度器件发 光性能的影响。研究发现:当X 为23nm、Y为7nm时,器件的光效和色坐标都具有 很高的稳定性,在电压分别为5、 10和15V时,色坐标分别为(0.33,0.37)、(0.33,0. 37)和(0.34,0.38);在电压为 5V时,电流密度为0.674mA,亮度为158.7cd ,最大电流效率为26.87cd/A;利用电子阻 挡材料TCTA和空穴阻挡材料BCP能够显著提高载流子的复合效率。分析认为:发光层顺序 为红绿/蓝时,更有利于蓝光的出射,从而使白光的色坐标更稳定。     

NPB/Alq3双层有机电致发光器件薄膜厚度与器件性能的优化

研究了以NPB为空穴传输层、Alq₃为发光层的双层异质结有机电致发光器件的薄膜厚度对器件性能的影响.制备了一系列具有不同NPB和Alq₃厚度的器件并测试了其电致发光特性.结果表明,器件电流随Alq₃与NPB厚度变化的关系并不相同.不同有机层厚度双层器件的电流机制符合陷阱电荷限制(TCL)理论,随外加电压的增大,器件电流经历了欧姆电导区、TCL电流区、陷阱电荷限制-空间电荷限制(TCL-SCL)过渡区三个区域的变化.当有机层厚度匹配为NPB(20nm)/Alq₃(50nm)时可以获得性能优良的器件.器件的流明效率-电压关系曲线的变化规律是在低电压区较快达到最大值,然后随电压的增加逐渐降低.     

Influence of Disassociation Probability on External Quantum Efficiency in Organic Electrophosphorescent Devices

An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence（EPH） devices. The charge recombination process and the triplet（T）-triplet（T） annihilation processes are taken into account in this model. The influences of applied voltage and the thickness of the device on the disassociation probability, and of current density and the thickness of the device on the external quantum efficiency are studied thoroughly by including and ignoring the disassociation of excitons. It is found that the dissociation probability of excitons will come close to 1 at high electric field, and the external EPH quantum efficiency is almost the same at low electric field. There is a large discrepancy of the external EPH quantum efficiency at high electric field for including or ignoring the disassociation of excitons.     

Recombination Efficiency and Width in Bilayer Organic Light-emitting Devices

A bilayer model with ohmic anode contact and injection limited cathode contact has been proposed to calculate the recombination efficiency and recombination zone width of the device. The effects of the thickness of hole transport layer and the barriers of organic/organic interface on the combination efficiency and recombination width have been discussed. It is found that： （1） When the electrons are blocked fully and the holes are not blocked significantly at the organic/organic interface, for a given Lh/L, the recombination efficiency increases with increasing the applied voltage, but at a higher applied voltage, the recombination efficiency decreases with increasing Lh/L; （2） The recombination efficiency increases with increasing applied voltage and Hh＇, and when applied voltage and Hh＇ exceed some value, the recombination efficiency appears as a plateau; （3） The recombination width decreases with increasing the applied voltage and Lh/L. This model might explain the relative experiment phenomena.     

GaAs/AlGaAs环形激光器的量子阱结构优化

为了研究量子阱结构对半导体环形激光器阈值电流的影响,从F-P腔激光器的振荡条件出发,分析了半导体环形激光器的阈值电流密度与量子阱结构参量的函数关系,并推导出最佳量子阱数的表达式。利用器件仿真软件ATLAS建立环形激光器的等效模型,仿真、分析了不同工作温度下,量子阱数、阱厚及势垒厚度对阈值电流的影响。结果表明,阈值电流随量子阱数和阱厚的增加先减小后增大,存在一组最佳值;在确定合适的量子阱数和阱厚后,相对较窄的势垒厚度有助于进一步降低阈值电流;采用GaAs/AlGaAs材料体系和器件结构,其最佳量子阱结构参量为M=3,dw=20nm及db=10nm。     

Low Roll‐Off Perovskite Quantum Dot Light‐Emitting Diodes Achieved by Augmenting Hole Mobility

The external quantum efficiencies (EQEs) of perovskite quantum dot light‐emitting diodes (QD‐LEDs) are close to the out‐coupling efficiency limitation. However, these high‐performance QD‐LEDs still suffer from a serious issue of efficiency roll‐off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non‐radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll‐off of 11% at 500 mA cm^?2 (the lowest roll‐off known so far) where the EQE is still over 11%.     

Analysis of interface recombination and self-absorption effect on the performance of QWIP-HBT-LED integrated device

In this paper, the effect of interface recombination and self-absorption within the light emitting diode (LED) active region on the efficiency of QWIP-HBT-LED integrated device is considered. This device is composed of a quantum well infrared photodetector (QWIP), a heterojunction bipolar transistor (HBT) and an LED. The evaluation is based on solving the continuity equation describing the carrier diffusion within the LED active region. Analytical expression describing the effect of self-absorption and surface recombination on the LED quantum efficiency is derived. In addition, the active region width and all interested device parameters are involved. It is observed that the quantum conversion efficiency of the device under consideration is degraded by the self-absorption and interface recombination within the recombined region of the LED. Also, the quantum conversion efficiency of the device is increased with the increase of the LED active region as long as the recombination velocity is above a specified value, while it is decreased with the increase of the LED active region as long as the recombination velocity is below this specified value.     

固态照明用蓝光LED和LD辐射量子效率与电流密度的比较研究

比较了蓝光LED和LD的辐射量子效率随电流密度变化的趋势.LED在低电流密度时具有很高的辐射量子效率,并且在电流密度为24.4 A/cm2时达到了峰值效率,随着电流密度的增大,其量子效率会急剧下降;LD在电流密度低于出光阈值时辐射量子效率为零,待达到出光阈值后迅速上升并在电流密度为4.85×103 A/cm2时超越LED.分析表明,LED效率骤减是由于自身的发光机理限制了辐射速率的提升;LD受激辐射发光机理恰好弥补了LED的不足,其辐射量子效率受非辐射复合速率的影响较小.结果表明,LD具有高电流密度下高辐射量子效率的特性.     

Channeled substrate nonplanar laser analysis--Part II: Lasers with tapered active regions

Light versus current (LversusI) characteristics are calculated for double-heterostructure diode lasers whose active regions decrease in thickness laterally from a maximum on axis. This variation produces lateral real refractive index waveguiding which in turn stabilizes the spatial mode such that the modal field becomes anastigmatic and theLversusIplot becomes linear. In addition to determining threshold current and differential quantum efficiency, we compute the TE00mode patterns, active region charge density distribution, and the power levelP*_{1}at which spatial hole burning causes the TE01mode to begin lasing. The maximum power density at the facet for that power levelP*_{1}is also obtained. All these characteristics are presented as functions of the various device parameters including carrier spontaneous recombination time, diffusion length, optical gain, unpumped band-to-band absorption, internal losses, antiguidance index, wavelength, cladding Al content, active region dimensions, current spreading resistance, facet reflectivity, laser length, and stripe width. Utilizing this information, a design is developed for a laser with low threshold current (40-50 mA) and high differential quantum efficiency (50-65 percent) that operates stable single lowest order (TE00) spatial mode to powers well in excess of 50 mW.     

Modelling of a Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript>Te/ZnTe Single Quantum Well for Laser Diodes

In this paper, the carrier density, temperature and quantum well width effect have been investigated for the optical gain for a Cd_1?xZn_xTe/ZnTe Zinc-blend strained quantum well structure. The device emits laser radiations in green–yellow–orange. Our results showed that the optical gain significantly increases with the increasing of the carrier density. It also increases with the decreasing of the Zn concentration, the well width and the temperature. In addition, the optimal threshold current density values were determined for three alloy compositions as 0.7, 0.8 and 0.9.     

Temperature-dependent characteristics of 1.3-μm AlGaInAs-InPlasers with multiquantum barriers at the guiding layers

Strain-compensated 1.3-μm AlGaInAs-InP multiquantum-well (MQW) lasers with multiquantum barriers at both the n- and p-type guiding layers are comprehensively studied. The laser exhibits a characteristic temperature as high as 95 K and degradation in slope efficiency as low as -1.06 dB in the temperature range from 25°C to 75°C. The characteristic temperature of transparency current density is deduced to be 129 K. It is also found that the internal loss increases slowly with temperature, while the temperature dependence of the internal quantum efficiency dominates the degradation of the external quantum efficiency due to the degradation of the stimulated recombination, and significant increase of electron and hole leakage at high temperature     

Well-defined electrical properties of high-strain resonant interband tunneling structure

The GaAs/InAs high-strain resonant interband tunneling diodes (HSRITDs) have been implemented by metal organic chemical vapor deposition (MOCVD). The current-voltage characteristics of variable quantum well and barrier thickness grown on (1 1 1) GaAs substrates are investigated. Experimental results reveal that the quantum barrier and well layer will influence current-voltage properties such as the peak current density, valley current density, and peak-to-valley current ratio (PVCR). Both peak current and valley current density decrease with increasing layers width. This result also exhibits the variation of PVCR with layers width.