Enhanced Light Extraction From Triangular GaN-Based Light-Emitting Diodes

This study investigated the characteristics of a triangular light-emitting diode (LED) and compared it to a standard quadrangular LED. The total radiant flux from the packaged triangular LED increased by 48% and 24% at input currents of 20 and 100 mA, respectively, compared to that of a quadrangular LED which was grown on patterned sapphire substrate. In light far-field beam distribution, the light extraction in the horizontal direction of the LED was much higher than that of the quadrangular LED due to the enhancement of light emission from the side walls of the triangular LED.     

Light Extraction From Solution-Based Processable Electrophosphorescent Organic Light-Emitting Diodes

Molecular dye dispersed solution processable blue emitting organic light-emitting devices have been fabricated and the resulting devices exhibit efficiency as high as 25 cd/A. With down-conversion phosphors, white emitting devices have been demonstrated with peak efficiency of 38 cd/A and luminous efficiency of 25 lm/W. The high efficiencies have been a product of proper tuning of carrier transport, optimization of the location of the carrier recombination zone and, hence, microcavity effect, efficient down-conversion from blue to white light, and scattering/isotropic remission due to phosphor particles. An optical model has been developed to investigate all these effects. In contrast to the common misunderstanding that light out-coupling efficiency is about 22% and independent of device architecture, our device data and optical modeling results clearly demonstrated that the light out-coupling efficiency is strongly dependent on the exact location of the recombination zone. Estimating the device internal quantum efficiencies based on external quantum efficiencies without considering the device architecture could lead to erroneous conclusions     

Electron and Hole Capture Cross-Sections of Fe Acceptors in GaN:Fe Epitaxially Grown on Sapphire

Carrier trapping of Fe³⁺/Fe²⁺ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels on the order of 10¹⁸ cm⁻³, the luminescence decay times are strongly dependent on the Fe concentration, indicating that Fe centers act as predominant nonradiative recombination channels. Linear dependence of the decay time on the iron concentration allows estimation of the electron capture cross-section for the Fe³⁺ ions, which is equal to 1.9 × 10⁻¹⁵ cm². The upper bound for the cross-section of the hole capture of Fe²⁺ was evaluated as 1 × 10⁻¹⁵ cm².     

Improvement of Light Extraction From Patterned Polymer Encapsulated GaN-Based Flip-Chip Light-Emitting Diodes by Imprinting

To improve surface light extraction of GaN-based flip-chip light-emitting diodes (FC-LEDs), we employed an imprint approach of thermosetting polymer for patterning microscale surface grating on the polymer encapsulant. One-dimensional (1-D) and two-dimensional (2-D) taper-like polymer gratings with a period of 6 mum were successfully realized on encapsulant above the sapphire backplane of GaN LED. By adopting the 1-D and 2-D taper-like grating encapsulant, the improvement of light extraction from the 1 mm times 1 mm FC-blue LED with a reflective Ag film on the p-side was about 18.5% and 31.9% compared to the LED encapsulated by flat polymer, respectively. To evaluate the concept of a diffraction grating in enhancement of light extraction, we performed a simulation of diffraction based on 1-D rigorous coupled wave analysis with the supporting experiments.     

Transmission Electron Microscopy-Based Analysis of Electrically Conductive Surface Defects in Large Area GaSb Homoepitaxial Diodes Grown Using Molecular Beam Epitaxy

We investigate a mechanism causing shorting of large area GaSb diodes grown on GaSb substrates using molecular beam epitaxy (MBE). The source of these shorts is determined to be large crystallographic defects on the surface of the diodes that are formed around droplets of gallium ejected from the gallium Knudsen cells during MBE. The gallium droplets cause defects in the crystal structure, and, as the epitaxy continues, the gallium is incorporated into the surrounding material. The shape of the defects is pyramidal with a central void extending from the epi-surface to the gallium core. Processing a GaSb diode with these surface defects results in the top-side contact metal migrating into the defect and shorting the diode. This prevents realization of large area diodes that are critical to applications such as photovoltaics and detectors. The diodes in this study are electrically characterized and the defect formation mechanism is investigated using cross-section transmission electron microscopy and electron dispersive spectroscopy.     

Ultra-Low-Voltage Schottky-Barrier Field-Enhanced Electron Emission From Gold Nanowires Electrochemically Grown in Modified Porous Alumina Templates

Superior field emission (FE) action has been observed from a tailored array of gold nanowires (AuNWs) grown in porous anodic alumina (PAA) templates. The turn-on voltage was found to be 0.2 V, which is far less than the values reported earlier for diamond-coated cathodes and carbon nanotubes (CNTs). Furthermore, the FE current was unaffected by the ambient gas pressure. Such a low-voltage FE is attributed here to the formation of a Schottky barrier at the interface of gold and amorphous alumina scales that remain on the AuNWs.     

空穴阻挡层对有机发光二极管寿命的影响

为研究空穴阻挡层对有机发光二极管寿命的影响,制备了含有空穴阻挡层的典型双层结构有机发光二极管,其中八羟基喹啉铝(Alq3)为发光层和电子传输层,BCP 为空穴阻挡层.器件的寿命随着发光层的厚度减小而降低,实验结果表明积累在发光层的空穴和激子可能是影响器件寿命的主要原因之一.     

阳极氧化铝工艺用于提高LED的出光效率

使用纳米尺度的多孔阳极氧化铝(anodic aluminum oxide,AAO)作为刻蚀掩膜,刻蚀氧化铟锡(indium-tin oxide,ITO),形成纳米图形化表面,对于发光二极管的出光效率有明显的提升作用。AAO纳米掩膜的制备已广为报道,是纳电子学研究中常用的模板之一,工艺简单易行、可控性好。使用电感耦合反应离子刻蚀方法成功将纳米多孔结构转移到ITO上,形成ITO纳米结构。纳米图形化结构的引入使得器件有效减小了内部的全反射,在电压没有大幅提高,注入电流350 mA时,光学输出提高了7%。纳米尺度粗化结构LED与传统结构LED对比,提升了器件的外量子效率。     

大功率GaN基LED的提取效率

影响GaN基LED效率的主要因素是内量子效率和提取效率.蓝光GaN基的LED内量子效率可达70%以上,紫外GaN基LED可达80%,进一步改善的空间较小.而传统大面积结构GaN基LED由于全反射和吸收等原因,外提取效率只有百分之几,提高空间很大.本文从几何和物理光学角度分析了影响GaN基LED外提取效率的因素,针对全反射、吸收、横向光波导等问题总结了现有的各种提高GaN基LED提取效率的手段及其优缺点.     

Water‐Soluble Lacunary Polyoxometalates with Excellent Electron Mobilities and Hole Blocking Capabilities for High Efficiency Fluorescent and Phosphorescent Organic Light Emitting Diodes

High performance solution‐processed fluorescent and phosphorescent organic light emitting diodes (OLEDs) are achieved by water solution processing of lacunary polyoxometalates used as novel electron injection/transport materials with excellent electron mobilities and hole blocking capabilities. Green fluorescent OLEDs using poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐(1,4‐benzo‐{2,1′,3}‐thiadiazole)] (F8BT) as the emissive layer and our polyoxometalates as electron transport/hole blocking layers give a luminous efficiency up to 6.7 lm W^?1 and a current efficiency up to 14.0 cd A^?1 which remained nearly stable for about 500 h of operation. In addition, blue phosphorescent OLEDs (PHOLEDs) using poly(9‐vinylcarbazole) (PVK):1,3‐bis[2‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazo‐5‐yl]benzene (OXD‐7) as a host and 10.0 wt% FIrpic as the blue dopant in the emissive layer and a polyoxometalate as electron transport material give 12.5 lm W^?1 and 30.0 cd A^?1 power and luminous efficiency, respectively, which are among the best performance values observed to date for all‐solution processed blue PHOLEDs. The lacunary polyoxometalates exhibit unique properties such as low electron affinity and high ionization energy (of about 3.0 and 7.5 eV, respectively) which render them as efficient electron injection/hole blocking layers and, most importantly, exceptionally high electron mobility of up to 10^?2 cm² V^?1 s^?1.     

大功率GaN基LED的提取效率

影响GaN基LED效率的主要因素是内量子效率和提取效率. 蓝光GaN基的LED内量子效率可达70%以上， 紫外GaN基LED可达80%，进一步改善的空间较小. 而传统大面积结构GaN基LED由于全反射和吸收等原因，外提取效率只有百分之几，提高空间很大. 本文从几何和物理光学角度分析了影响GaN基LED外提取效率的因素，针对全反射、吸收、横向光波导等问题总结了现有的各种提高GaN基LED提取效率的手段及其优缺点.     

大功率GaN基LED的提取效率

影响GaN基LED效率的主要因素是内量子效率和提取效率.蓝光GaN基的LED内量子效率可达70%以上,紫外GaN基LED可达80%,进一步改善的空间较小.而传统大面积结构GaN基LED由于全反射和吸收等原因,外提取效率只有百分之几,提高空间很大.本文从几何和物理光学角度分析了影响GaN基LED外提取效率的因素,针对全反射、吸收、横向光波导等问题总结了现有的各种提高GaN基LED提取效率的手段及其优缺点.     

Measurement of Electron Mobility in Alq3 From Optical Modulation Measurements in Multilayer Organic Light-Emitting Diodes

The dynamic characteristics of multilayer organic light-emitting diodes (OLEDs) determine the refresh rate in display applications, and are of great importance for practical organic displays. They also serve as an important tool in studying the transport mechanisms in organic conductors. Here, the modulation characteristics of several conventional small-molecule OLED structures [consisting of ITO/PEDOT:PSS(50 nm)/TPD(50 nm)/Alq₃(various)/LiF(1 nm)/Al(90 nm)] are measured and analyzed in terms of mobility in and thickness of the Alq ₃ layer. Their optical response was shown to be limited by electron transport across the Alq₃. Extracted electron mobilities were about 2-4times10^-6 cm²/Vmiddots (consistent with that reported in the literature) and near-identical values for mobility were obtained from devices of different thicknesses, suggesting that this method measures mobility independent of interface trap charging. This novel technique is a complement to large signal time of flight or delay time measurements (which can include interface and trap charging during the measurement) and can serve as a flexible method to study transport in actual devices     

GaN基激光器电子阻挡层的优化分析

从载流子输运机制的角度,分析了影响GaN基激光器中有源区电流溢出的因素,对AlGaN电子阻挡层中Al组分和p型掺杂水平进行了优化.结果表明,当p型掺杂水平增高时,所需要的势垒高度减小,即Al组分减小.     

A Pyridine‐Containing Anthracene Derivative with High Electron and Hole Mobilities for Highly Efficient and Stable Fluorescent Organic Light‐Emitting Diodes

A pyridine‐containing anthracene derivative, 9,10‐bis(3‐(pyridin‐3‐yl)phenyl)anthracene (DPyPA), which comprehensively outperforms the widely used electron‐transport material (ETM), tris(8‐quinolinolato) aluminum (Alq₃), is synthesized. DPyPA exhibits ambipolar transport properties, with both electron and hole mobilities of around 10^?3 cm^?2 V^?1 s^?1; about two orders of magnitude higher than that of Alq₃. The nitrogen atom in the pyridine ring of DPyPA coordinates to lithium cations, which leads to efficient electron injection when LiF/Al is used as the cathode. Electrochemical measurements demonstrate that both the cations and anions of DPyPA are stable, which may improve the stability of devices based on DPyPA. Red‐emitting, green‐emitting, and blue‐emitting fluorescent organic light emitting diodes with DPyPA as the ETM display lower turn‐on voltages, higher efficiencies, and stronger luminance than the devices with Alq₃ as the ETM. The power efficiencies of the devices based on DPyPA are greater by 80–140% relative to those of the Alq₃‐based devices. The improved performance of these devices is attributed to the increased carrier balance. In addition, the device employing DPyPA as the ETM possesses excellent stability: the half‐life of the DPyPA‐based device is 67 000 h—seven times longer than that of the Alq₃‐based device—for an initial luminance of 5000 cd m^?2.     

GaN基激光器电子阻挡层的优化分析

从载流子输运机制的角度,分析了影响GaN基激光器中有源区电流溢出的因素,对AlGaN电子阻挡层中Al组分和p型掺杂水平进行了优化.结果表明,当p型掺杂水平增高时,所需要的势垒高度减小,即Al组分减小.     

3C-SiC/Si异质结二极管的高温特性

研究了低压化学气相淀积方法制备的n-3C-SiC/p-Si(100)异质结二极管(HJD)在300～480K高温下的电流密度-电压(J-V)特性.室温下HJD的正反向整流比(通常定义为±1V外加偏压下)最高可达1.8×104,在480K时仍存在较小整流特性,整流比减小至3.1.在300K温度下反向击穿电压最高可达220V.电容-电压特性表明该SiC/Si异质结为突变结,内建电势Vbi为0.75V.采用了一个含多个参数的方程式对不同温度下异质结二极管的正向J-V实验曲线进行了很好的拟和与说明,并讨论了电流输运机制.该异质结构可用于制备高质量异质结器件,如宽带隙发射极SiC/Si HBT等.     

Efficient All-Perovskite White Light-Emitting Diodes Made of In Situ Grown Perovskite-Mesoporous Silica Nanocomposites

Metal halide perovskite quantum dots (QDs) have emerged as potential materials for high brightness, wide color gamut, and cost-effective backlight emission due to their high photoluminescence quantum yields, narrow emission linewidths, and tunable bandgaps. Herein, CsPbX₃/SBA-15 nanocomposites are prepared with outstanding optical properties and high stability through an in situ growth strategy using mesoporous silica particles. According to finite-difference time-domain simulations, the mesoporous structure provides a strong waveguide effect on perovskite QDs and the uniform dispersion suppresses reabsorption losses, improving the overall photoconversion efficiency of perovskite QDs. The as-fabricated perovskite monochromatic light-emitting diode (LED) has a maximum luminous efficiency of 183 lm W⁻¹, which is the highest for monochromatic perovskite LEDs reported to date. A further benefit of this work is that the white devices, which combine the green and red perovskite nanocomposites with commercial blue LED, exhibit a high luminous efficiency of 116 lm W⁻¹ and a wide color gamut (125% for NTSC and 94% for Rec. 2020) with coordinates of (0.33,0.31).     

3C-SiC/Si异质结二极管的高温特性

研究了低压化学气相淀积方法制备的n-3C-SiC/p-Si(100)异质结二极管(HJD)在300～480K高温下的电流密度-电压(J-V)特性.室温下HJD的正反向整流比(通常定义为±1V外加偏压下)最高可达1.8×104,在480K时仍存在较小整流特性,整流比减小至3.1.在300K温度下反向击穿电压最高可达220V.电容-电压特性表明该SiC/Si异质结为突变结,内建电势Vbi为0.75V.采用了一个含多个参数的方程式对不同温度下异质结二极管的正向J-V实验曲线进行了很好的拟和与说明,并讨论了电流输运机制.该异质结构可用于制备高质量异质结器件,如宽带隙发射极SiC/Si HBT等.     

3C-SiC/Si异质结二极管的高温特性

研究了低压化学气相淀积方法制备的n- 3C- Si C/p- Si(10 0 )异质结二极管(HJD)在30 0～4 80 K高温下的电流密度-电压(J- V)特性.室温下HJD的正反向整流比(通常定义为±1V外加偏压下)最高可达1.8×10 4 ,在4 80 K时仍存在较小整流特性,整流比减小至3.1.在30 0 K温度下反向击穿电压最高可达2 2 0 V .电容-电压特性表明该Si C/Si异质结为突变结,内建电势Vbi为0 .75 V.采用了一个含多个参数的方程式对不同温度下异质结二极管的正向J-V实验曲线进行了很好的拟和与说明,并讨论了电流输运机制.该异质结构可用于制备高质量异质结器件,如宽带隙发射极Si C/Si HBT