Browsing by Author "Leung, K. M."

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Enhanced light output from a nitride-based power chip of green light-emitting diodes with nano-rough surface using nanoimprint lithography
(2008-05-07)
Huang, H. W.
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Lin, C. H.
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Yu, C. C.
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Chiu, C. H.
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Lai, C. F.
Enhanced light extraction from a GaN-based power chip (PC) of green light-emitting diodes (LEDs) with a rough p-GaN surface using nanoimprint lithography is presented. At a driving current of 350 mA and with a chip size of 1 mm x 1 mm packaged on transistor outline (TO)-cans, the light output power of the green PC LEDs with nano-rough p-GaN surface is enhanced by 48% when compared with the same device without a rough p-GaN surface. In addition, by examining the radiation patterns, the green PC LED with nano-rough p-GaN surface shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices by using the technique of nanoimprint lithography under suitable nanopattern design.
Enhanced light output power of GaN-based vertical-injection light-emitting diodes with a 12-fold photonic quasi-crystal by nano-imprint lithography
(2009-08-12)
Huang, H. W.
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Lin, C. H.
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Lee, K. Y.
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Yu, C. C.
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Huang, J. K.
GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a 12-fold photonic quasi-crystal (PQC) by nano-imprint lithography (NIL) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 mu m x 350 mu m, the light output power of our thin-film LED with a 12-fold PQC structure reaches 41 mW. This result is an enhancement of 78% when compared with the output power of a VLED without a PQC structure. In addition, the corresponding light radiation pattern shows a narrower beam shape due to the strong guided light extraction effect by the formed PQC structure in the vertical direction.
Enhanced vertical extraction efficiency from a thin-film InGaN-GaN light-emitting diode using a 2-D photonic crystal and an omnidirectional reflector
(2008-05-01)
Lin, C. H.
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Yen, H. H.
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Lai, C. F.
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Huang, H. W.
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Chao, C. H.
An InGaN-GaN thin-film vertical-type light-emitting diode with a two-dimensional photonic crystal (PC) on the emitting surface and a TiO2-SiO2 onmidirectional reflector on the bottom was fabricated. The device was investigated by performing a series of experiments and numerical computations. Electroluminescence measurement revealed a strong extraction enhancement in the vertical direction at 433-nm wavelength. The emission spectrum of the light was found to be strongly modified by the PC to have a significantly narrow linewidth of 5 nm. Our experimental results were in accord with those obtained from our numerical findings.
Enhancement of InGaN-GaN indium-tin-oxide flip-chip light-emitting diodes with TiO2-SiO2 multilayer stack omnidirectional reflector
(2006-09-01)
Lin, C. H.
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Lai, C. F.
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Ko, T. S.
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Huang, H. W.
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Kuo, H. C.
Enhancement of light extraction of GaN-based flip-chip indium-tin-oxide light-emitting diodes (FC ITO LEDs) with an onmidirectional reflector (ODR) is presented. The ODR consisting of alternating layers of TiO2 and SiO2 is designed to possess a complete photonic bandgap within the blue region of interest, and it is fabricated by E-beam deposition. At a driving current of 300 mA and a chip size of 1 mm x 1 mm, the light output power of the FC ITO LEDs with the ODR reaches 156 mW. This is an enhancement of 31% when compared with the same device with an Al mirror instead. Furthermore, by examining the radiation patterns, the FC ITO LED with the ODR shows stronger enhancement around the vertical direction. Our work offers promising potential for enhancing output powers of commercial light-emitting devices.
Fabrication and characteristics of thin-film InGaN-GaN light-emitting diodes with TiO2/SiO2 omnidirectional reflectors
(2007-07-01)
Chiu, C. H.
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Kuo, H. C.
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Lee, C. E.
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Lin, C. H.
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Cheng, P. C.
In this paper, a novel GaN-based thin-film vertical injection light-emitting diode (LED) structure with a TiO2 and SiO2 omnidirectional reflector (ODR) and an n-GaN rough surface is designed and fabricated. The designed ODR, consisting of alternating TiO2 and SiO2, layers possesses a complete photonic band gap within the blue region of interest. The arrays of the conducting channels are integrated into the TiO2/SiO2 ODR structure for vertically spreading the current. Assisted by the laser lift-off and photo-enhanced chemically etched surface roughening process, the light output power and the external quantum efficiency of our thin-film LED with a TiO2/SiO2 ODR (at a driving current of 350 mA and with chip size of 1 mm x 1 mm) reached 330 mW and 26.7%, increased by 18% and 16%, respectively, compared with the results from the thin-film LED with an Al mirror. By examining the radiation patterns of the LEDs, the optical output power mainly increased within the 120 deg cone due to the higher reflectance of the TiO2/SiO2 ODR within the blue regime.
High-performance GaN-based vertical-injection light-emitting diodes with TiO2-SiO2 omnidirectional reflector and n-GaN roughness
(2007-03-01)
Huang, H. W.
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Kuo, H. C.
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Lai, C. F.
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Lee, C. E.
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Chiu, C. W.
We have designed and fabricated a new type of GaN-based thin-film vertical-injection light-emitting diode (LED) with TiO2-SiO2 onmidirectional reflector (ODR) and n-GaN roughness. The associated ODR designed for LED operation wavelength at 455 nm vias integrated with patterned conducting channels for the purpose of vertical current spreading. With the help of laser lift-off and. photo-electrochemical etching technologies, at a driving current of 350 mA and with chip size of 1 mm x 1 mm, the light-output power and the external quantum efficiency of our thin-film LED with TiO2-SiO2 ODR reached 330 mW and 26.7%. The result demonstrated 18% power enhancement when compared with the results from the thin-film LED with Al reflector replace.
Improvement of light output in GaN-based power chip light-emitting diodes with a nano-rough surface by nanoimprint lithography
(2008-04-01)
Huang, H. W.
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Lin, C. H.
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Yu, C. C.
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Lee, B. D.
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Chiu, C. H.
The enhancement of light extraction of gallium nitride (GaN)-based power chip (PC) light-emitting diodes (LEDs) with a p-GaN rough surface by nanoimprint lithography (NIL) is presented. At a driving current of 350 mA and a chip size of 1 mm x 1 mm, the light output power of the PC LEDs with a p-GaN rough surface (etching depth from 130 to 150 nm) showed an enhancement of 24% on wafer when compared with the same device without NIL. Current-voltage results indicated an ohmic contact by the increase in the contact area of the nano-roughened surface at 200 mA. This paper offers a promising potential for enhancing the output powers of commercial LEDs.
Investigation of GaN-based vertical-injection light-emitting diodes with GaN nano-cone structure by ICP etching
(2008-07-25)
Huang, H. W.
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Lin, C. H.
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Yu, C. C.
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Lee, K. Y.
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Lee, B. D.
The GaN-based thin-film vertical-injection LEDs (VLEDs) with GaN nano-cone structures are fabricated and presented. Under the process conditions of fixed Cl(2)/Ar now rate of 10/25sccm and ICP/bias power of 200/200W, the GaN nano-cone structures are self-assembly formed with variable density of 1.5 x 10(7) to 1.4 x 10(1) cm(-2) and variable depth of 0.56-1.34 mu m when varying the ICP chamber pressure. At a driving current of 350mA and with chip size of 1 mm x 1 mm, the light output power of our thin-film LED with a specific GaN nano-cone structure reaches 224 mW which is enhanced by 160% when compared with the output power of conventional VLED. In addition, the corresponding light radiation pattern Shows Much higher light intensity Clue to the strong light scattering effect by the formed nano-cone Structure. (C) 2008 Elsevier B.V. All rights reserved.
Investigation of InGaN/GaN power chip light emitting diodes with TiO(2)/SiO(2) omnidirectional reflector
(2008-12-01)
Huang, H. W.
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Lin, C. H.
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Yu, C. C.
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Lee, B. D.
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Kuo, H. C.
Enhancements of light extraction of GaN-based power chip (PC) LEDs with and without rough surface on p-GaN and TiO(2)/SiO(2) omnidirectional reflector (ODR) on the bottom are presented. Motivated by phosphor-conversion white light applications, the peak-emitting wavelength of our studied PC LEDs is chosen to be 455 nm and the fabricated ODR is designed for the same wavelength regime. At a driving current of 350 mA and a chip size of 1 mm x 1 mm on a TO-can package, the light output power of the PC LED with ODR on the bottom and pit type of rough surface on p-GaN is enhanced by 67% when compared with the same device without ODR and rough surface. Furthermore, by examining the radiation patterns, the PC LED with the ODR and rough surface shows stronger enhancement around the vertical direction. Our results provide promising potential to increase output powers of commercial light emitting devices, especially for white light applications.
Light extraction enhancement of InGaN-based green LEDs with a composite omnidirectional reflector
(2006-12-01)
Lin, C. H.
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Kuo, H. C.
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Lai, C. F.
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Huang, H. W.
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Leung, K. M.
We have designed, fabricated and measured the electroluminescence of InGaN-based green light-emitting diodes ( LEDs) having composite omni-directional reflectors ( ODRs) deposited on their backside. The composite ODR is composed of a stack of two individual ODRs, each of which is made of alternating layers of TiO2 and SiO2 with a thickness ratio that gives the largest possible 1D photonic bandgap. The lattice constants of these individual ODRs are chosen so that the effective bandgap of the resulting ODR completely covers the emission spectrum of the LEDs. The effective bandgap of our ODR extends from 498 nm to 548 nm. At a driving current of 300 mA, and with the LED emission peak at about 525 nm and a FWHM of about 35 nm, the light output powers of the LED with the composite ODR and the LED with a conventional Ti/Al metal reflector are found to be 52.9 mW and 40.7 mW, respectively. This 30% light extraction enhancement can be attributed to our composite ODR which has a higher reflectance, a lower optical absorption and a wider reflection angle compared with the Ti/Al reflector.