Search query: WLP "light emitting diode"

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abstract: Since the successful demonstration of a blue light emitting diode (LED)1, potential materials for making short wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow2,3,4. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation5,6. Several groups have postulated the use of p type ZnO doped with nitrogen, arsenic or phosphorus7,8,9,10, and even p n junctions11,12,13. However, the choice of dopant and growth technique remains controversial and the reliability of p type ZnO is still under debate14. If ZnO is ever to produce long lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors15. Here we report high quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p type ZnO reproducibly. Violet electroluminescence from homostructural p i n junctions is demonstrated at room temperature.
author_names: Atsushi Tsukazaki

Akira Ohtomo

Takeyoshi Onuma

M Ohtani

Takayuki Makino

Masatomo Sumiya

Keita Ohtani

Shigefusa F Chichibu

Shunro Fuke

Yusaburo Segawa

Hideo Ohno

Hideomi Koinuma

Masashi Kawasaki
title: Repeated temperature modulation epitaxy for p type doping and light emitting diode based on ZnO
year: 2004

abstract: Stretchability will significantly expand the applications scope of electronics, particularly for large area electronic displays, sensors and actuators. Unlike for conventional devices, stretchable electronics can cover arbitrary surfaces and movable parts. However, a large hurdle is the manufacture of large area highly stretchable electrical wirings with high conductivity. Here, we describe the manufacture of printable elastic conductors comprising single walled carbon nanotubes (SWNTs) uniformly dispersed in a fluorinated rubber. Using an ionic liquid and jet milling, we produce long and fine SWNT bundles that can form well developed conducting networks in the rubber. Conductivity of more than 100 S cm( 1) and stretchability of more than 100% are obtained. Making full use of this extraordinary conductivity, we constructed a rubber like stretchable active matrix display comprising integrated printed elastic conductors, organic transistors and organic light emitting diodes. The display could be stretched by 30 50% and spread over a hemisphere without any mechanical or electrical damage.
author_names: Tsuyoshi Sekitani

Hiroyoshi Nakajima

Hiroki Maeda

Takanori Fukushima

Takuzo Aida

Kenji Hata

Takao Someya
title: Stretchable active matrix organic light emitting diode display using printable elastic conductors.
venue: Nature materials
year: 2009

abstract: Compact high efficiency ultraviolet solid state light sources such as light emitting diodes (LEDs) and laser diodes are of considerable technological interest as alternatives to large, toxic, low efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid state light sources are also attracting attention for potential applications in high density optical data storage, biomedical research, water and air purification, and sterilization. Wide bandgap materials, such as diamond and III V nitride semiconductors (GaN, AlGaN and AlN; refs 3 10) are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n type and p type doping in aluminium nitride (AlN) which has a very wide direct bandgap of 6 eV. This doping strategy allows us to develop an AlN PIN (p type/intrinsic/n type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton related light emitting devices as well as replacing gas light sources with solid state light sources.
author_names: Yoshitaka Taniyasu

Makoto Kasu

Toshiki Makimoto
title: An aluminium nitride light emitting diode with a wavelength of 210 nanometres
venue: Nature
year: 2006

abstract: In this study, we determined the effects of raising seedlings with different light spectra such as with blue, red, and blue red light emitting diode (LED) lights on seedling quality and yield of red leaf lettuce plants. The light treatments we used were applied for a period of 1 week and consisted of 100 mmol*m 2 *s 1 of blue light, simultaneous irradiation with 50 mmol*m 2 *s 1 of blue light and 50 mmol*m 2 *s 1 of red light, and 100 mmol*m 2 *s 1 of red light. At the end of the light treatment, that is 17 days after sowing (DAS) the leaf area and shoot fresh weight (FW) of the lettuce seedlings treated with red light increased by 33% and 25% respectively, and the dry weight of the shoots and roots of the lettuce seedlings treated with blue containing LED lights increased by greater than 29% and greater than 83% compared with seedlings grown under a white fluorescent lamp (FL) The shoot/root ratio and specific leaf area of plants irradiated with blue containing LED lights decreased. At 45 DAS, higher leaf areas and FWs were obtained in lettuce plants treated with blue containing LED lights. The total chlorophyll (Chl) contents in lettuce plants treated with blue containing and red lights were less than that of lettuce plants treated with FL, but the Chl a/b ratio and carotenoid content increased under blue containing LED lights. Polyphenol contents and the total antioxidant status (TAS) were greater in lettuce seedlings treated with blue containing LED lights than in those treated with FL at 17 DAS. The higher polyphenol contents and TAS in lettuce seedlings at 17 DAS decreased in lettuce plants at 45 DAS. In conclusion, our results indicate that raising seedlings treated with blue light promoted the growth of lettuce plants after transplanting. This is likely because of high shoot and root biomasses, a high content of photosynthetic pigments, and high antioxidant activities in the lettuce seedlings before transplanting. The compact morphology of lettuce seedlings treated with blue LED light would be also useful for transplanting.
author_names: Masahumi Johkan

Kazuhiro Shoji

Fumiyuki Goto

Shin-nosuke Hashida

Toshihiro Yoshihara
title: Blue Light emitting Diode Light Irradiation of Seedlings Improves Seedling Quality and Growth after Transplanting in Red Leaf Lettuce
year: 2010

abstract: A facile method for the preparation of silver nanoparticles (AgNPs) of various sizes and morphologies, including dodecahedra, nanorods, and nanoplates, has been discovered. By choosing the desired optical properties (absorption maximum) and irradiating spherical AgNP seeds with a selected light emitting diode, we achieve control over the size, morphology, and optical properties. The properties of AgNPs are intrinsically dependent on the size and shape of the particles, which can be readily controlled with the strategies reported here. Literature methods for the synthesis of anisotropic AgNPs require complex solutions containing seed nanoparticles with specific twinning defects, and a variety of specific stabilizing ligands direct the growth of the seeds but limit the versatility of the particles. In general, these thermal routes to anisotropic AgNPs give particles with high polydispersity, limiting their applications in single molecule spectroscopy and surface plasmon resonance spectroscopy. We describe a single photochemical method for preparation of AgNPs with predictable and controllable size and morphology that are produced from a single source of photochemically grown AgNP seeds stabilized only by sodium citrate. We also describe a common mechanism for the formation of the various types of AgNPs.
author_names: Kevin G Stamplecoskie

Juan C Scaiano
title: Light emitting diode irradiation can control the morphology and optical properties of silver nanoparticles.
venue: Journal of the American Chemical Society
year: 2010

abstract: The high frequency modulation of individual pixels in III nitride based micro pixel light emitting diode arrays, where each array consists of 16 x 16 individually addressable 72 mm diameter pixels, are reported. The devices investigated have peak emission wavelengths at 370, 405, and 450 nm, respectively. The optical 3 dB modulation bandwidth of a typical pixel from the 450 nm emitting device was found to be approximately 245 MHz. Data transmission at rates of up to 1 Gb/s is demonstrated from a single pixel emitting at 450 nm, using on off keying nonreturn to zero modulation, with a bit error ratio of less than 1 x 10 10. Such devices have potential for free space or fiber coupled visible light communications.
author_names: Jonathan J D McKendry

R Green

Anthony E Kelly

Zheng Gong

B J E Guilhabert

David Massoubre

Erdan Gu

Martin D Dawson
title: High Speed Visible Light Communications Using Individual Pixels in a Micro Light Emitting Diode Array
venue: IEEE Photonics Technology Letters
year: 2010

abstract: The electrochemical growth of ZnO nanowire arrays on p type GaN (0001) single crystalline thin films supported on sapphire is demonstrated for the first time. The wires were directly epitaxially grown on the GaN with the relationship ZnO(0001)[1010]GaN(0001)[1010] By glancing angle XRD experiments, the ZnO mosaicity was shown to be as low as 1.2deg. The deposited ZnO NWs exhibited a very low density of intrinsic defects as demonstrated by micro Raman and photoluminescence (PL) experiments. The only significant PL emission of the heterojunction at room temperature was the near band edge one of ZnO at 382 nm. After integration of the heterostructure in a solid state light emitting diode device, a rectifying behavior was found with a forward current onset at 3 V. The diodes emitted an unique UV light centered at 397 nm for either as prepared or annealed samples. The emission threshold voltage was 4.4 V. The violet visible tail of the emission could be observed above 5 6 V with the naked eyes. The present r.
author_names: Oleg Lupan

Thierry Pauporte

Bruno Viana

Ion M Tiginyanu

Veaceslav V Ursaki

Robert Cortes
title: Epitaxial Electrodeposition of ZnO Nanowire Arrays on p GaN for Efficient UV Light Emitting Diode Fabrication
year: 2010

abstract: The optical properties of YAG:Ce phosphor were measured by a double integrating sphere system and calculated by Mie theory and Monte Carlo ray tracing to provide precise optical characterizations of YAG:Ce phosphor for white light emitting diode (LED) packaging design. Measurement results showed that the phosphor presents strong absorption for blue light, high reflection for yellow light, and an isotropic emission pattern of converted light. The conversion efficiency and quantum efficiency for the saturated phosphor are around 70% and 87% respectively. Based on the measurement results, the absorption coefficient, scattering coefficient, and anisotropy factor of the phosphor calculated by Mie theory were compared with those calculated by ray tracing simulation to modify Mie theory to find a reasonable method that can easily obtain the optical constants of YAG:Ce phosphor. Comparisons revealed that Mie theory can predict the variation of the optical constants of phosphor, but the absorption and scattering cross sections should be multiplied with two fitting parameters. The fitting parameters have been given in this study and can be obtained by testing packaged LEDs with different phosphor concentrations.
author_names: Zongyuan Liu

Sheng Liu

Kai Wang

Xiaobing Luo
title: Measurement and numerical studies of optical properties of YAG:Ce phosphor for white light emitting diode packaging.
venue: Applied optics
year: 2010

abstract: (112 0) A plane AlN p n junction light emitting diode (LED) with a wavelength of 210 nm is demonstrated. The electroluminescence from the A plane LED is inherently polarized for the electric field parallel to the [0001] c axis due to a negative crystal field splitting energy. The polarization ratio (electric field component ratio of parallel and perpendicular to c axis) is as high as 0.9. The radiation pattern of the A plane LED shows higher emission intensity along the surface normal, while that of a conventional (0001) C plane LED shows lower emission intensity along the surface normal. The different radiation patterns can be explained by the polarization property.
author_names: Yoshitaka Taniyasu

Makoto Kasu
title: Surface 210 nm light emission from an AlN p n junction light emitting diode enhanced by A plane growth orientation
year: 2010

abstract: Abstract 3,12 Dimethoxy 7,8 dicyano [5]helicene (DDH) was introduced as a novel emissive material for organic light emitting diode. It shown good thermal stability and no glass transition temperature was observed. The LUMO, HOMO and energy band gap 3.3, 5.9 and 2.6 eV) of this compound were determined using cyclic voltammetry technique. Fluorescence quantum yield of DDH in chloroform is 0.27. The turn on voltage of OLEDs with a configuration of ITO/PEDOT:PSS/DDH/Ca/Al was not a function of DDH thickness in a range of 60 100 nm. The best OLED, in which DDH thickness was 100 nm, exhibited a turn on voltage of 3.7 V with maximum brightness of 1587 cd/m 2 at 8.0 V and 281 mA/cm 2 The maximum current efficiency and power efficiency were 0.64 cd/A and 0.29 lm/W, respectively. The CIE coordinates of the OLED electroluminescence, however, appeared to depend on the applied voltage as they were (0.38,0.47) at 5.0 V and (0.51,0.44) at 8.0 V.
author_names: Somboon Sahasithiwat

Tipwan Mophuang

Laongdao Menbangpung

Siriporn Kamtonwong

Thanasat Sooksimuang
title: 3,12 Dimethoxy 7,8 dicyano [5]helicene as a novel emissive material for organic light emitting diode
year: 2010