Mg fluctuation in p-GaN layers and its effects on InGaN/GaN blue light-emitting diodes dependent on p-GaN growth temperature

Correlation between material properties of bulk p-GaN layers grown on undoped GaN and device performance of InGaN/GaN blue light-emitting diodes (LEDs) as a function of p-GaN growth temperature were investigated. The p-GaN layers of both structures grown by metal-organic chemical-vapor deposition were heavily doped with Mg. As the growth temperature of the bulk p-GaN layer increased up to 1,080°C, N_A-N_D increased. However, above 1,110°C, N_A-N_D sharply decreased, while the fluctuation of Mg concentration ([Mg]) increased. At this time, a peculiar surface, which originated from inversion domain boundaries (IDBs), was clearly observed in the bulk p-GaN layer. The IDBs were not found in all LEDs because the p-GaN contact layer was relatively thin. The change in photoluminescence emission from the ultraviolet band to blue band is found to be associated with the fluctuation of [Mg] and IDBs in bulk p-GaN layers. The LED operating voltage and reverse voltage improved gradually up to the p-GaN contact-layer growth temperature of 1,080°C. However, the high growth temperature of 1,110°C, which could favor the formation of IDBs in the bulk p-GaN layer, yielded poorer reverse voltage and saturated output power of the LEDs.     

Electrical and luminescent properties and the spectra of deep centers in GaMnN/InGaN light-emitting diodes

Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external magnetic field (so-called “spin-LEDs”). The contact annealing temperature was kept to 750°C, which is the thermal stability limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and the n-GaN in the top contact layer.     

Fluorene derivatives for highly efficient non-doped single-layer blue organic light-emitting diodes

Diphenylamino- and triazole-endcapped fluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been synthesized and characterized. Single-layer electroluminescent devices of these fluorene derivatives exhibited efficient deep blue to greenish blue emission at low driving voltage. The single-layer OLED of PhN-OF(1)-TAZ shows a maximum current efficiency of 1.54 cd/A at 20 mA cm⁻² with external quantum efficiency (EQE) of 2.0% and CIE coordinates of (0.153, 0.088) in deep blue region, while the single-layer device of oligothienylfluorene PhN-OFOT-TAZ shows a maximum brightness of 7524 cd/m² and a maximum current efficiency of 2.9 cd/A with CIE coordinates of (0.20, 0.40) in greenish blue.     

Straight forward synthesis of conjugated polymers for deep red to NIR PLED containing chlorine atoms on the backbone

High molecular weight and non-crosslinking conjugated donor–acceptor copolymers with chlorine on the backbones were straight forward synthesized for the first time under Stille condensation reaction by using the different reaction activities between chlorine and bromine atoms. The chlorine-bearing polymers exhibited much lower LUMO, larger Stokes shift and lower self-absorption compared with the non-chloride analogue, for the electron affinity and large steric hindrance of chlorine atoms. Deep red to NIR emission centered at 698 nm was obtained with brightness about 1500 cd/m² and centered at 708 nm was obtained with brightness over 400 cd/m² based on dopant/host system.     

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。     

功能聚合物：从薄膜器件到纳米器件

文章简要回顾了功能聚合物的发现和发展历程,着重介绍了其在发光二极管、太阳能电池、场效应晶体管、传感器件、纳米材料与器件中的应用.     

Robust Laminated Anode with an Ultrathin Titanium Nitride Layer for High-Efficiency Top-Emitting Organic Light-Emitting Diodes

The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits.     

Improved efficiency in green polymer light-emitting diodes with air-stable electrodes

By dispersing an electron transporting molecular dopant into the active semiconducting luminescent polymer, we have achieved improved efficiencies for green light-emitting diodes (LEDs). These green emitting LEDs were fabricated by adding an electron transporting molecular dopant, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (PBD), into the semiconducting luminescent polymer as the emitting layer in the polymer LEDs. The devices used poly(2-cholestanoxy-5-thexyldimethylsilyl-l,4-phenylene vinylene) (CS-PPV), a new soluble green light emitter, as the semiconducting luminescent polymer and either aluminum or indium as the electron injection electrodes. Quantum efficiencies of LEDs with the electron transporting molecular additive in the luminescent polymer and an Al electrode are about 0.3% photons per electron, better by a factor of 18 than similar devices made without the addition of the electron transport molecular dopant; quantum efficiencies of similar LEDs fabricated with an In electrode are 0.23% photons per electron, better by a factor of 16 than devices without the electron transport molecular additive.     

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.