Browsing by Author "Chao, C. L."

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Beam Shaping of GaN/InGaN Vertical-Injection Light Emitting Diodes via High-Aspect-Ratio Nanorod Arrays
(2009)
Tsai, M. A.
;
Yu, Peichen
;
Chao, C. L.
;
Chiu, C. H.
;
Kuo, H. C.
The enhanced light extraction and collimated output beam profile from GaN/InGaN vertical-injection light emitting diodes are demonstrated utilizing high-aspect-ratio nanorod arrays. The nanorod arrays are patterned by self-assembled silica spheres, followed by inductively-coupled-plasma reactive-ion-etching. (C) 2008 Optical Society of America
Demonstration of slow light via population oscillation in quantum dot VCSEL
(2007)
Xuan, R.
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Chi, J. Y.
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Peng, P. C.
;
Yang, H. P.
;
Chao, C. L.
Experimental data for slow light delay in a quantum dot VCSEL are analyzed with a Fabry-Perot analysis. The analysis can fit the observed wavelength dependence of the delay. It can also explain that the maximum delay occur at a wavelength detuned from the resonant frequency.
Efficiency Enhancement and Beam Shaping of GaN-InGaN Vertical-Injection Light-Emitting Diodes via High-Aspect-Ratio Nanorod Arrays
(2009-01-01)
Tsai, Min-An
;
Yu, Peichen
;
Chao, C. L.
;
Chiu, C. H.
;
Kuo, H. C.
The enhanced light extraction and collimated output beam profile from GaN-InGaN vertical-injection light-emitting diodes (VI-LEDs.) are demonstrated utilizing high-aspect-ratio nanorod arrays. The nanorod arrays are patterned by self-assembled silica spheres, followed by inductively coupled-plasma reactive ion etching. The fabricated nanorod arrays not only provide an omnidirectional escaping zone for photons, but also serve as waveguiding channels for the emitted light, resulting in a relatively collimated beam profile. The light output power of the VI-LED with nanorod arrays is enhanced by 40 %, compared to a conventional VI-LED. The measured far-field profiles indicate that the enhancement is mainly along the surface normal direction, within a view angle of 20 degrees.
Efficiency enhancement of UV/blue light emitting diodes via nanoscaled epitaxial lateral overgrowth of GaN on a SiO(2) nanorod-array patterned sapphire substrate
(2008-11-15)
Chiu, C. H.
;
Li, Zhen-Yu
;
Chao, C. L.
;
Lo, M. H.
;
Kuo, H. C.
High-quality GaN layer was successfully grown on a SiO(2) nanorod-array patterned sapphire substrate (NAPSS) using metal-organic chemical vapor deposition by a nanoscaled epitaxial lateral overgrowth (NELO) method. From tunneling electron microscope images, well coalescence and turned dislocations are parallel to the surface direction were clearly observed. The Raman shift measurement shows the residual stress in GaN was greatly reduced from 1.359 to 0.652 GPa when compared to a GaN on flat sapphire substrate. Also, a high-efficiency GaN-based light-emitting diodes (LEDs) were demonstrated on the NELO NAPSS GaN, the respective output power and external quantum efficiency of the NELO NAPSS LEDs were estimated to be 22 mW and 40.2% at an injection current of 20 mA, showing an enhancement factor of 52% over conventional LEDs. The significant improvement resulted from both the enhanced light extraction assisted by the NAPSS, and the reduced dislocation densities using the NELO method. (c) 2008 Published by Elsevier B.V.
Efficiency enhancement of UV/blue light emitting diodes via nanoscaled epitaxial lateral overgrowth of GaN on a SiO2 nanorod-array patterned sapphire substrate
(2008-11-15)
Chiu, C. H.
;
Li, Zhen-Yu
;
Chao, C. L.
;
Lo, M. H.
;
Kuo, H. C.
High-quality GaN layer was successfully grown on a SiO2 nanorod-array patterned sapphire substrate (NAPSS) using metal-organic chemical vapor deposition by a nanoscaled epitaxial lateral overgrowth (NELO) method. From tunneling electron microscope images, well coalescence and turned dislocations are parallel to the surface direction were clearly observed. The Raman shift measurement shows the residual stress in GaN was greatly reduced from 1.359 to 0.652 GPa when compared to a GaN on flat sapphire substrate. Also, a high-efficiency GaN-based light-emitting diodes (LEDs) were demonstrated on the NELO NAPSS GaN, the respective output power and external quantum efficiency of the NELO NAPSS LEDs were estimated to be 22 mW and 40.2% at an injection current of 20 mA, showing an enhancement factor of 52% over conventional LEDs. The significant improvement resulted from both the enhanced light extraction assisted by the NAPSS, and the reduced dislocation densities using the NELO method. (c) 2008 Published by Elsevier B.V.
Enhancement of light output intensity by integrating ZnO nanorod arrays on GaN-based LLO vertical LEDs
(2008)
Chiu, C. H.
;
Lee, C. E.
;
Chao, C. L.
;
Cheng, B. S.
;
Huang, H. W.
Enhancement of light output intensity for GaN-based vertical light-emitting diodes (LEDs), combining wafer bonding and the laser lift-off (LLO) process, employing an omnidirectional extraction surface with synthesized single-crystal ZnO nanorod arrays in aqueous solution at room temperature is presented. The light output intensity and wall-plug efficiency of the GaN-based LLO vertical LED with the omnidirectional extraction surface by ZnO nanorod arrays shows 38.9 and 41.2% increases, respectively, at 200 mA current injections compared to that of a vertical LED without ZnO nanorod arrays. The ZnO nanorod arrays not only support a current spreading layer but enhance the probability of photon escape through the omnidirectional extraction surface. (C) 2008 The Electrochemical Society.
Freestanding high quality GaN substrate by associated GaN nanorods self-separated hydride vapor-phase epitaxy
(2009-08-03)
Chao, C. L.
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Chiu, C. H.
;
Lee, Y. J.
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Kuo, H. C.
;
Liu, Po-Chun
This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide (SiO(2)) were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy (HVPE). The passivation of the sidewalls coated with SiO(2) prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.
Nanoscale epitaxial lateral overgrowth of GaN-based light-emitting diodes on a SiO(2) nanorod-array patterned sapphire template
(2008-08-25)
Chiu, C. H.
;
Yen, H. H.
;
Chao, C. L.
;
Li, Z. Y.
;
Yu, Peichen
High efficiency GaN-based light-emitting diodes (LEDs) are demonstrated by a nanoscale epitaxial lateral overgrowth (NELO) method on a SiO(2) nanorod-array patterned sapphire substrate (NAPSS). The transmission electron microscopy images suggest that the voids between SiO(2) nanorods and the stacking faults introduced during the NELO of GaN can effectively suppress the threading dislocation density. The output power and external quantum efficiency of the fabricated LED were enhanced by 52% and 56%, respectively, compared to those of a conventional LED. The improvements originated from both the enhanced light extraction assisted by the NAPSS and the reduced dislocation densities using the NELO method. (C) 2008 American Institute of Physics.