Browsing by Author "Lai, C. F."

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Azimuthal anisotropy of light extraction from photonic crystal light-emitting diodes
(2007)
Hsuch, H. T.
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Wang, J. -F. T.
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Chao, C. H.
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Yeh, W. Y.
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Chi, J. Y.
Photonic crystal light-emitting diodes exhibiting anisotropic light extraction efficiency have been investigated experimentally and theoretically. Images of the anisotropy in the azimuthal direction are obtained using annular structures with triangular lattice. Depending on the lattice constants, 6-fold symmetric patterns with varying number of petals are obtained.
Efficiency enhancement of GaN-based power-chip LEDs with sidewall roughness by natural lithography
(2007)
Huang, Hung-Wen
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Lai, C. F.
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Wang, W. C.
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Lu, T. C.
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Kuo, H. C.
This study reports the development of GaN-based power-chip light-emitting diodes (LEDs) with sidewall roughness using natural lithography with polystyrene spheres as the etching mask. At an injection current of 350 mA, the LED with sidewall roughness increased the light output intensity of the InGaN/GaN multiple quantum well LEDs by a factor of 1.26, indicating that the LED with sidewall roughness had larger light extraction efficiency. The wall-plug efficiency of GaN-based LED was increased by 26.5% with sidewall roughness. After 1000 h life test, it was found that normalized output power of power-chip LED with sidewall roughness did not show any significant degradation. (c) 2006 The Electrochemical Society.
Enhanced light extraction of InGaN-based green LEDs by nano-imprinted 2D photonic crystal pattern
(2008-05-01)
Cheng, B. S.
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Chiu, C. H.
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Huang, K. J.
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Lai, C. F.
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Kuo, H. C.
In this paper, we propose a simple, low cost and mass producible nanoimprint lithography (NIL) method to texture the surface of GaN-based light emitting diodes (LEDs) with a two-dimensional photonic crystal (2DPC). Such a 2DPC structure not only enhanced the light output power but also changed the far-field pattern simultaneously. Also, a TiO(2)/SiO(2) omnidirectional reflector (ODR) was deposited on the backside of the LEDs to further increase the light output power. Under 350 mA current injection, it was found that forward voltages were 3.35, 3.34 and 3.75 V while the light output powers of the LEDs were 59.5, 92.5 and 112.1 mW for the conventional LED, the PCLED with 20 nm depth, and the PCLED with 120 nm depth all with chip size of 1 mm x 1 mm, respectively. A 88.4% enhancement in light output power of PCLED with a 120 nm depth and ODR on the backside could be achieved when compared to the conventional LED under the driving current of 350 mA. From the measurement results, it was also found that the NIL process does not degrade the electrical properties of the fabricated LEDs.
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 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.
Enhancement of InGaN/GaN flip-chip ITO LEDs with incline sidewalls coated with TiO2/SiO2 omnidirectional reflector
(2007)
Chiu, 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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Wang, W. C.
The light extraction enhancement of GaN-based flip-chip indium-tin oxide light-emitting diodes (FC ITO LEDs) with an inclined sidewall coated with TiO2/SiO2 omnidirectional reflectors (ODRs) is presented. At a driving current of 350 mA and a chip size of 1x1 mm, the light output power and the light extraction enhancement of the FC ITO LEDs coated TiO2/SiO2 ODRs with inclined sidewall reached 183 mW and 15% when compared with the results from the same device, FC ITO LEDs coated TiO2/SiO2 ODRs with vertical sidewall. Furthermore, by examining the radiation patterns of the FC ITO LEDs, the increased optical power within 150 degrees cone contributed to the stronger enhancement around the vertical direction of an inclined sidewall ODR within blue regime. Our work offers promising potential for enhancing output powers of commercial light-emitting devices. (c) 2007 The Electrochemical Society.
Fabrication of InGaN/GaN nanorod light-emitting diodes with self-assembled Ni metal islands
(2007-11-07)
Chiu, C. H.
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Lu, T. C.
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Huang, H. W.
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Lai, C. F.
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Kao, C. C.
We report the fabrication of InGaN/GaN nanorod light-emitting diodes (LEDs) using inductively coupled plasma reactive-ion etching (ICP-RIE) and a photo-enhanced chemical (PEC) wet oxidation process via self-assembled Ni nanomasks. An enhancement by a factor of six times in photoluminescence (PL) intensities of nanorods made with the PEC process was achieved in comparison to that of the as-grown structure. The peak wavelength observed from PL measurement showed a blue shift of 3.8 nm for the nanorods made without the PEC oxidation process and 8.6 nm for the nanorods made with the PEC oxidation process from that of the as-grown LED sample. In addition, we have demonstrated electrically pumped nanorod LEDs with the electroluminescence spectrum showing more efficiency and a 10.5 nm blue-shifted peak with respect to the as-grown LED sample.
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.
Hole shape effect of photonic crystals on the guided resonance modes in GaN-based ultra-thin film-transferred light-emitting diodes
(2010)
Lai, C. F.
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Chao, C. H.
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Kuo, H. C.
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Yu, P.
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Yeh, W. Y.
The guided resonance mode affected the different hole shapes of photonic crystals in GaN ultra-thin film-transferred light-emitting diodes. The ellipse-hole PhC extracted a fewer modes than the regular PhC due to the lattice symmetry break. @2010 Optical Society of America
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.
InGaN/GaN MQW Nanorods LED Fabricated by ICP-RIE and PEC Oxidation Processes
(2007-01-01)
Lai, Fang-, I
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Huang, H. W.
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Chiu, Ching-Hua
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Lai, C. F.
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Lu, T. C.
The InGaN/GaN nanorods LED was successfully fabricated by ICP-RIE and PEC processes. Compared with as-grown sample, the PL and EL peak-wavelengths of the nanorods with PEC show 8.6 and 10.5 nm blue-shift, respectively. (c) 2007 Optical Society of America
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.
Optical properties of In0.3Ga0.7N/GaN green emission nanorods fabricated by plasma etching
(2007-08-22)
Chiu, C. H.
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Lo, M. H.
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Lai, C. F.
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Lu, T. C.
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Huang, H. W.
In this study, we have fabricated In0.3Ga0.7N/GaN green emission nanorods and demonstrated optical enhancement by photoluminescence (PL) measurements. An enhancement factor of 3.5 and an emission peak blue-shift of 6.6 nm were observed at 300 K for the green emission nanorods structure in comparison to the as-grown flat surface structure. The blue-shift phenomenon from the nanorod structure could be caused by a partial reduction of the internal piezoelectric field. However, the similar carrier decay time for the green emission nanorod structure and the as-grown flat surface structure observed in low-temperature time-resolved PL measurements indicates that the dominant optical enhancement mechanism of the green emission nanorod structure could be mainly resulting from the large emission surface areas and the multiple scattering paths between the nanorods.