Blue Light Emitting Diodes (blue + light_emitting_diode)

Distribution by Scientific Domains
Physics and Astronomy85%

Selected Abstracts

A Wide-Bandgap Semiconducting Polymer for Ultraviolet and Blue Light Emitting Diodes,

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2003
Ping Lu
Abstract A novel wide-bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene-based copolymer composed of rigid twisting segments in the main-chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V. By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd,·,m,2 was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain-aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors. The structure of the copolymer PDHFSCHD. [source]

Blue light emitting diode fabricated on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Y. Naoi
Abstract We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Blue light emitting diodes on Si(001) grown by MOVPE

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007
F. Schulze
The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. [source]

Laser-doping of silicon carbide for p,n junction and LED fabrication

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007
Sachin Bet
Abstract The high melting point and the limited diffusion of impurities in silicon carbide have greatly restricted the use of conventional ion implantation and furnace to incorporate and activate dopants. A laser doping technique overcomes these obstacles for doping silicon carbide and other wide band gap semiconductors. This paper presents the work on fabrication of p,n junction diodes and blue light emitting diodes using laser doping technique. A p,n junction was created by laser doping a silicon carbide wafer with aluminum (p-type) and nitrogen (n-type). Optical interferometer profilometer scan showed that there was no damage on the surface post laser doping. Secondary ion mass spectrometry (SIMS) was carried to estimate the dopant concentration and depth. The effects of laser doping on the current,voltage characteristics were studied. The junctions were characterized by capacitance,voltage and electroluminescence measurements. A broad electroluminescence peak was observed around 498.8 nm wavelength, characterizing the p,n junction as a blue light-emitting diode. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Blue light emitting diode fabricated on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Y. Naoi
Abstract We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Degradation of blue LEDs related to structural disorder

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
A. V. Kamanin
Abstract The degradation of blue light emitting diodes (LEDs) with different structural disorder based on MQW InGaN/GaN grown by MOCVD on sapphire has been investigated. New approach to analyze the degradation has been used. It takes into account the structural disorder determined by the extended defect system relaxation and related with poor coalescence of the mosaic structure domains. The results obtained leads to assumption that the migration and segregations of Ga on domain dislocation boundaries of the mosaic structure and the change of energy activation of Mg related centers are important reasons of degradation for all types of LEDs The fastest degradation for poor ordered LEDs was observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Integration of CdSe quantum dots with GaN optoelectronic materials

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
J. G. Pagan
Abstract Material structures on the nanoscale can enable enhancement of optoelectronic device performance. For example, in the InGaN active layers of MOCVD grown blue light emitting diodes, indium segregation plays a critical role in the interplay between blue luminescent channels and non-radiative recombination centers such as crystal defects. Unfortunately, high efficiency luminescence of InGaN does not extend into the "deep green" spectral region, around the wavelength of peak human eye response. We are investigating whether commercially available luminescent nanostructures such as CdSe quantum dots can be incorporated into III-nitride devices to extend their high-efficiency performance into the "deep green". Surfactant stabilized CdSe particles in liquid dispersions are drop-cast onto HVPE grown GaN. Physical properties of resultant CdSe surface structures are examined. Luminescence is reported before and after subsequent growth of GaN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]