Thermal Modeling of Organic Light-Emitting Diode Display Panels

Power densities required to operate active-matrix organic-light-emitting diode (AMOLED) based displays for high luminance applications, lead to temperature rise due to self heating. Temperature rise leads to significant degradation and consequent reduction in life time. In this work numerical techniques based computational fluid dynamics (CFD) is used to determine the temperature rise and its distribution for an AMOLED based display for a given power density and size. Passive cooling option in form of protruded rectangular fins is implemented to reduce the display temperature.

Efficiency measurement of GaN-based quantum well and light-emitting diode structures grown on silicon substrates

The optical efficiency of GaN-based multiple quantum well (MQW) and light emitting diode (LED) structures grown on Si(111) substrates by metal-organic vapor phase epitaxy was measured and compared with equivalent structures on sapphire. The crystalline quality of the LED structures was comprehensively characterized using x-ray diffraction, atomic force microscopy, and plan-view transmission electron microscopy. A room temperature photoluminescence (PL) internal quantum efficiency (IQE) as high as 58% has been achieved in an InGaN/GaN MQW on Si, emitting at 460 nm. This is the highest reported PL-IQE of a c-plane GaN-based MQW on Si, and the radiative efficiency of this sample compares well with similar structures grown on sapphire. Processed LED devices on Si also show good electroluminescence (EL) performance, including a forward bias voltage of ∼3.5 V at 20 mA and a light output power of 1 mW at 45 mA from a 500 ×500 μm2 planar device without the use of any additional techniques to enhance the output coupling. The extraction efficiency of the LED devices was calculated, and the EL-IQE was then estimated to have a maximum value of 33% at a current density of 4 A cm-2, dropping to 30% at a current density of 40 A cm-2 for a planar LED device on Si emitting at 455 nm. The EL-IQE was clearly observed to increase as the structural quality of the material increased for devices on both sapphire and Si substrates. © 2011 American Institute of Physics.

Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique

We report on the realization of ZnO homojunction light-emitting diodes (LEDs) fabricated by metalorganic chemical vapor deposition on (0001) ZnO bulk substrate. The p-type ZnO epilayer was formed by nitrogen incorporation using N2O gas as oxidizing and doping sources. Distinct electroluminescence (EL) emissions in the blue and yellow regions were observed at room temperature by the naked eye under forward bias. The EL peak energy coincided with the photoluminescence peak energy of the ZnO epilayer, suggesting that the EL emissions emerge from the ZnO epilayer. In addition, the current-voltage and light output-voltage characteristics of ZnO homojunction LEDs have also been studied. (c) 2006 American Institute of Physics.

Room temperature all-silicon photonic crystal nanocavity light emitting diode at sub-bandgap wavelengths

Silicon is now firmly established as a high performance photonic material. Its only weakness is the lack of a native electrically driven light emitter that operates CW at room temperature, exhibits a narrow linewidth in the technologically important 1300-1600 nm wavelength window, is small and operates with low power consumption. Here, an electrically pumped all-silicon nano light source around 1300-1600 nm range is demonstrated at room temperature. Using hydrogen plasma treatment, nano-scale optically active defects are introduced into silicon, which then feed the photonic crystal nanocavity to enhance the electrically driven emission in a device via Purcell effect. A narrow (Δλ=0.5 nm) emission line at 1515 nm wavelength with a power density of 0.4mW/cm2 is observed, which represents the highest spectral power density ever reported from any silicon emitter. A number of possible improvements are also discussed, that make this scheme a very promising light source for optical interconnects and other important silicon photonics applications. © 2012 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

The performance enhancement in organic light-emitting diode using a semicrystalline composite for hole injection

A semicrystalline composite, 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) doped N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), has been fabricated and characterized. An organic light-emitting diode using such a composite in hole injection exhibits the improved performance as compared with the reference device using neat NPB in hole injection. For example, at a luminance of 2000 cd/m(2), the former device gives a current efficiency of 2.0cd/A, higher than 1.6cd/A obtained from the latter device. Furthermore, the semicrystalline composite has been shown thermally to be more stable than the neat NPB thin film, which is useful for making organic light emitting diodes with a prolonged lifetime.

Tunnel Junction AlGaInP Light Emitting Diode

The n-type GaAs substrates are used and their conductive type is changed to p-type by tunnel junction for AlGaInP light emitting diodes (TJ-LED), then n-type GaP layer is used as current spreading layer. Because resistivity of the n-type GaP is lower than that of p-type, the effect of current spreading layer is enhanced and the light extraction efficiency is increased by the n-type GaP current spreading layer. For TJ-LED with 3μm n-type GaP current spreading layer, experimental results show that compared with conventional LED with p-type GaP current spreading layer, light output power is increased for 50% at 20mA and for 66.7% at 100mA.

A High Power Light Emitting Diode Module for Projection Display Application

Electron. Manuf. Packag. Technol. Soc. Chin. Inst. Electron.; IEEE Compon., Packag., Manuf. Technol. Soc. (IEEE-CPMT); Xidian University

A miniaturized fluorescence detector with a windowless flow cell using a light-emitting diode

A miniaturized fluorescence detector using a high-brightness light-emitting diode as an excitation source was constructed and evaluated. A windowless flow cell based on a commercial four-port cross fitting was designed to reduce the stray-light level and to eliminate the optical alignment. The observed detection limit for fluorescein was 26 nM in the continuous-flow mode. The error in the reproducibility of the responses was evaluated by the FIA method, and was found to be within 2% RSD.

Light-emitting-diode-induced fluorescence detector for capillary electrophoresis using optical fiber with spherical end

A simple fluorescence detector for capillary electrophoresis (CE) using a blue light-emitting-diode (LED) as excitation source is constructed and evaluated. An optical fiber was used to collect the fluorescence, and a flat end of the fiber was modified to spherical end, resulting in 50% increase of efficiency over the flat end. A simple device for optical alignment of the fibers and capillary column was designed. The concentration and mass detection limits for fluorescein were 1.8 x 10(-7) Mol l(-1) and 4.3 femol, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

Efficient red organic light-emitting diode sensitized by phosphorescent Ir compound

The efficiencies of red organic light-emitting diode (OLED) using tris-(8-hydroxy-quinoline)aluminum (Alq(3)) as host and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant were greatly increased by adding a small amount (0.3 wt%) of Ir compound, iridium(III) bis(3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-onato-N-',C-4) (acetyl acetonate) (Ir(C6)(2)(acac)), as a sensitizer

Fabrication of an integrated pixel with an organic light-emitting diode driven by copper phthalocyanine organic thin film transistors

An organic integrated pixel with organic light-emitting diodes (OLEDs) driven by organic thin film transistors (OTFTs) is fabricated by a greatly simplified processing. The OTFTs are based on copper phthalocyanine as the active medium and fabricated on indium-tin-oxide (ITO) glass with top-gate structure, thus an organic integrated pixel is easily made by integrating OLED with OTFT. The OTFTs show field-effect mobility of 0.4 cm(2) /Vs and on/off ratio of 10(3) order. The OLED is driven well and emits the brightness as large as 2100cd/m(2) at a current density of 14.6 mu A/cm(2) at -19.7 V gate voltage. This simple device structure is promising in the future large-area flexible OLED displays.

A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer

By utilizing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline:Li/MoO3 as an effective charge generation layer (CGL), we extend our recently demonstrated single-emitting-layer white organic light-emitting diode (WOLED) to realize an extremely high-efficiency tandem WOLED. This stacked device achieves maximum forward viewing current efficiency of 110.9 cd/A and external quantum efficiency of 43.3% at 1 mu A/cm(2) and emits stable white light with Commission Internationale de L'Eclairage coordinates of (0.34, 0.41) at 16 V. It is noted that the combination of effective single units and CGL is key prerequisite for realizing high-performance tandem WOLEDs.