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Kim E.H.,Korea University | Kim K.C.,Korea University | Kim D.H.,Korea University | Baek J.H.,Korean Photonics Technology Institute | Kim T.G.,Korea University
IEEE Journal of Quantum Electronics | Year: 2010

This article describes the successful fabrication of europium-silicate thin film phosphor and its application to InGaN/GaN white light-emitting diodes (LEDs) in order to improve the photometric properties of the LEDs, including their correlated color temperatures (CCT) and color rendering index (CRI). The europium-silicate compounds are deposited on GaN templates grown on sapphire substrates by RF-sputtering and then annealed at 1000 °C in an N2 ambient to form a thin film phosphor that produces yellow or red emissions. The thin film phosphor is then patterned with stripes to grow a GaN buffer layer by epitaxially laterally overgrown GaN (ELOG) techniques, on which LED structures are grown by metal organic chemical vapor deposition. The ELOG sample shows no pits on the surface, and the full widths at half maximum (FWHMs) of its X-ray rocking curve for the (002) and (102) planes are as low as 249 and 416 arcsec, respectively. The optical spectrum from the embedded thin film phosphor is adjusted to have a maximum intensity at 560600 nm and a FWHM as wide as 90 nm to make up for the low efficiency at these wavelengths of conventional YAG-based yellow phosphor. Finally, we observed a tristimulus coordinate (x, y)=(0.33, 0.39), CCT=5607 K, and CRI=77.6 from the white LEDs with thin film phosphor as compared with (x, y)=(0.30, 0.28), CCT=8467 K, and CRI=66.52 for the white LEDs without thin film phosphor. © 2006 IEEE. Source

Shin Y.C.,Korea University | Kim D.H.,Korea University | Kim E.H.,Korea University | Park J.-M.,Iowa State University | And 8 more authors.
IEEE Journal of Quantum Electronics | Year: 2010

We report the enhanced light extraction of a square lattice photonic crystal GaN LED with a lattice constant of 460 nm and holes with a depth of 500 nm drilled through InGaN/GaN multiple quantum wells (MQWs) using laser holography and inductively coupled plasma reactive ion etching. In spite of the etching through the MQWs leading to undesirable surface recombination, the photonic crystal LEDs exhibited 137 times higher light extraction than that of the LEDs without photonic crystals at 20 mA. Theoretical studies using the 3-dimensional finite-difference time domain method show that the increase of the extraction efficiency with increasing etch depth is due to the increase of the density of the leaky modes into the air. © 2009 IEEE. Source

Nam S.-Y.,Gwangju Institute of Science and Technology | Choi Y.-S.,Gwangju Institute of Science and Technology | Song Y.-H.,Korean Photonics Technology Institute | Jung M.-H.,KAIST | And 8 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2013

We report hybrid n-ZnO/i-InGaN/p-GaN solar cells in which the n-GaN layer of n-GaN/i-InGaN/p-GaN solar cell was replaced with n-type ZnO. In this study, inverted structures were used for hybrid ZnO/nitride solar cells where p-type GaN was first grown on sapphire substrate, followed by i-InGaN and n-ZnO layers. The as-fabricated device showed high series resistance and low energy conversion efficiency due to the formation of damaged p-GaN region during dry etching. On the other hand, formation of microrods on the p-GaN eased the removal of the damaged p-GaN resulting in significantly lowered series resistance and enhanced energy conversion efficiency. (a) n-ZnO/i-InGaN/p-GaN solar cell structure without microrods, (b) n-ZnO/i-InGaN/p-GaN solar cell structure with microrods, and (c) magnified image of the dashed box on (b). © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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