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Chih-Chiang Kao,
T C Lu, H W Huang,
J T Chu,
Y C Peng,
H H Yao,
J Y Tsai,
T T Kao,
H C Kuo,
S C Wang,
C F Lin
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ABSTRACT: The characteristics of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with 25 pairs AlN–GaN dis-tributed Bragg reflector (DBR) and eight pairs Ta 2 O 5 –SiO 2 DBR was investigated and analyzed under the optical pumping at room temperature. The GaN-based VCSEL emits a blue wavelength at 448 nm with a linewidth of 0.17 nm with a near-field emission spot diameter of about 3 m. The laser beam has a near linear polarization with a degree of polarization of about 84%. The laser shows a high spontaneous emission coupling efficiency of about 5 10 2 and a high characteristic temperature of about 244 K. Index Terms—AlN, distributed Bragg reflector (DBR), GaN, vertical-cavity surface-emitting laser (VCSEL).
; 18(1).
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ABSTRACT: In this paper, GaN-based LEDs with a SiO2 photonic quasi-crystal (PQC) pattern on an n-GaN layer by nano-imprint lithography (NIL) are fabricated and investigated. At a driving current of 20 mA on Transistor Outline (TO)-can package, the better light output power of LED III (d = 1.2 microm) was enhanced by a factor of 1.20. After 1000 h life test (55 degrees C/50 mA) condition, Normalized output power of LED with a SiO2 PQC pattern (LED III (d = 1.2 microm)) on an n-GaN layer only decreased by 5%. This results offer promising potential to enhance the light output power of commercial light-emitting devices using the technique of nano-imprint lithography.
Journal of Nanoscience and Nanotechnology 10/2010; 10(10):6363-8. · 1.56 Impact Factor
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ABSTRACT: We demonstrate a novel type of linear cascade green light-emitting diode (LED) arrays as a light source for in-car or harsh environment plastic optical fiber (POF) communications. To further enhance its dynamic and static performance, an InGaN layer is inserted between an n-type GaN cladding layer and InGaN-GaN multiple quantum wells as an efficient current spreading layer. Compared with the control device without that layer, our three-LED cascade array demonstrates a smaller turn-on voltage (9.3 versus 11 V at 20 mA) and a larger output power (25.5 versus 22.5 mW at 180 mA), corresponding to an enhancement of around 31% in wall-plug efficiency. Furthermore, under the constant voltage bias of an in-car battery (12 V), our three-LED array exhibits an electrical-to-optical 3-dB bandwidth (100 versus 40 MHz) performance superior to that of the control device. Even under high-temperature dynamic operation, we observe that the InGaN insertion layer gives strong enhancement of modulation speed with negligible degradation of the output power, unlike the red resonant-cavity LEDs conventionally used for POF. We achieve 200-Mb/s error-free transmission at 200°C which is the highest operation temperature among all the reported high-speed LEDs.
IEEE Photonics Technology Letters 08/2010; · 2.19 Impact Factor
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ABSTRACT: GaN-based LEDs with a SiO<sub>2</sub> oxide PQC pattern on an n-GaN layer by nanoimprint lithography are fabricated and investigated. At a driving current of 20 mA on a Transistor-Outline-can package, the light output power of LED III (d = 1.2 μm) was enhanced by a factor of 1.20. The internal-quantum-efficiency result offers promising potential to enhance the light output power of commercial light-emitting devices with a SiO<sub>2</sub> oxide PQC structure on an n-GaN layer.
IEEE Electron Device Letters 07/2010; · 2.85 Impact Factor
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ABSTRACT: The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS) and a SiO<sub>2</sub> 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on transistor-outline-can package, the light output powers of LED with a PSS and LED with a PSS and a SiO<sub>2</sub> PQC structure are enhanced by 35% and 48%, compared with the conventional LED. In addition, the higher output power of the LED with a PSS and a SiO<sub>2</sub> PQC structure is due to better reflectance on PSS and higher epitaxial quality on an n-GaN using a SiO<sub>2</sub> 12-fold PQC structure pattern. These results provide promising potential to increase output powers of commercial light-emitting devices.
IEEE Electron Device Letters 07/2010; · 2.85 Impact Factor
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ABSTRACT: We demonstrate cascade green light-emitting-diodes, which greatly release trade-off between output-power and speed and exhibits strong modulation-speed enhancement with negligible output-power degradation from room-temperature to 200°C operation. 200 Mbit/sec error-free transmission at 200°C can be achieved.
Optical Fiber Communication (OFC), collocated National Fiber Optic Engineers Conference, 2010 Conference on (OFC/NFOEC); 04/2010
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ABSTRACT: The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS) and a SiO 2 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on transistor-outline-can package, the light output powers of LED with a PSS and LED with a PSS and a SiO 2 PQC structure are enhanced by 35% and 48%, compared with the conventional LED. In addition, the higher output power of the LED with a PSS and a SiO 2 PQC structure is due to better reflectance on PSS and higher epitaxial quality on an n-GaN using a SiO 2 12-fold PQC structure pattern. These results pro-vide promising potential to increase output powers of commercial light-emitting devices. Index Terms—Gallium nitride (GaN), light-emitting diodes (LEDs), nanoimprint lithography (NIL), patterned sapphire substrate (PSS).
01/2010; 31.
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ABSTRACT: GaN (gallium nitride)-based light-emitting diodes (LEDs) with a nano-scale SiO 2 structure between a transparent indium-tin oxide (ITO) layer and p-GaN were fabricated. The forward voltage at 20 mA for a GaN-based LED with a SiO 2 nano-scale structure was slightly higher than that of a conventional GaN-based LED because the total area of the p-type metal contact between the transparent ITO layer and p-GaN was smaller. However, the light output power for the GaN-based LED with a nano-scale structured SiO 2 at 20 mA was 24% higher than that for a conventional GaN-based LED structure. This increase in the light output power is mostly attributed to the scattering of light from the SiO 2 photonic quasi-crystal (PQC) layer.
Semicond. Sci. Technol.161 SEMICONDUCTOR SCIENCE AND TECHNOLOGY Semicond. Sci. Technol. 01/2010; 25(25):65007-4.
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ABSTRACT: 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 µm × 350 µm, 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.
Semiconductor Science and Technology 07/2009; 24(8):085008. · 1.72 Impact Factor
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ABSTRACT: Enhancements of light extraction of GaN-based power chip (PC) LEDs with and without rough surface on p-GaN and TiO2/SiO2 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 × 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.
Semiconductor Science and Technology 10/2008; 23(12):125006. · 1.72 Impact Factor
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ABSTRACT: We have developed a simple method to fabricate nanoscale masks by using self-assembly Ni clusters formed through a rapid thermal annealing (RTA) process. The density and dimensions of the Ni nano-masks could be precisely controlled. The nano-masks were successfully applied to GaN-based light-emitting diodes (LEDs) with nano-roughened surface, GaN nanorods, and GaN-based nanorod LEDs to enhance light output power or change structure properties. The GaN-based LED with nano-roughened surface by Ni nano-masks and excimer laser etching has increased 55% light output at 20 mA when compared to that without the nano-roughened process. The GaN nanorods fabricated by the Ni nano-masks and ICP-RIE dry etching showed 3.5 times over the as-grown sample in photoluminescence (PL) intensity. The GaN-based nanorod LEDs assisted by photo-enhanced chemical (PEC) wet oxidation process were also demonstrated. The electroluminescence (EL) intensity of the GaN-based nanorod LED with PEC was about 1.76 times that of the as-grown LED. The fabrication, structure properties, physical features, and the optical and electrical properties of the fabricated devices will be discussed.
Journal of Lightwave Technology 07/2008; 26(11):1445-1454. · 2.78 Impact Factor
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ABSTRACT: A high emitting efficiency GaN-based white LED with 2D PQC on surface and PSS were successfully fabricated. After packaging, 21% enhancement in emitting luminous flux was achieved under the driving current 20 mA.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: An InGaN-GaN thin-film vertical-type light-emitting diode with a two-dimensional photonic crystal (PC) on the emitting surface and a TiO-SiO omnidirectional 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.
IEEE Photonics Technology Letters 06/2008; · 2.19 Impact Factor
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ABSTRACT: 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 × 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.
Nanotechnology 05/2008; 19(18):185301. · 3.98 Impact Factor
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ABSTRACT: An InGaN–GaN thin-film vertical-type light-emitting diode with a two-dimensional photonic crystal (PC) on the emitting surface and a TiO 2 –SiO 2 omnidirectional 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 ver-tical direction at 433-nm wavelength. The emission spectrum of the light was found to be strongly modified by the PC to have a signifi-cantly narrow linewidth of 5 nm. Our experimental results were in accord with those obtained from our numerical findings. Index Terms—Light-emitting diode (LED), omnidirectional re-flector (ODR), photonic crystal (PC).
01/2008; 20(15).
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ABSTRACT: The light extraction enhancement of
-based flip-chip indium-tin oxide light-emitting diodes (FC ITO LEDs) with an inclined sidewall coated with
omnidirectional reflectors (ODRs) is presented. At a driving current of
and a chip size of
, the light output power and the light extraction enhancement of the FC ITO LEDs coated
ODRs with inclined sidewall reached
and 15% when compared with the results from the same device, FC ITO LEDs coated
ODRs with vertical sidewall. Furthermore, by examining the radiation patterns of the FC ITO LEDs, the increased optical power
within 150° 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.
Journal of The Electrochemical Society. 10/2007; 154(11):H944-H947.
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C H Chiu,
M H Lo,
C F Lai,
T C Lu, H W Huang,
Y A Chang,
T H Hsueh,
C C Yu,
H C Kuo,
S C Wang,
C F Lin,
Y K Kuo
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ABSTRACT: 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.
Nanotechnology 07/2007; 18(33):335706. · 3.98 Impact Factor
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ABSTRACT: The temperature dependent performance of VCSELs based on sub-monolayer (SML) InGaAs quantum dots (QDs) with fully doped AlGaAs/GaAs DBRs is presented. The SML QD VCSEL shows extreme temperature insensitivity under high speed operated in 2.125 Gb/s from -40degC~100degC. The continue-wave (CW) light-current (LI) output characteristics of the laser is also studied.
Lasers and Electro-Optics, 2007 and the International Quantum Electronics Conference. CLEOE-IQEC 2007. European Conference on; 07/2007
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ABSTRACT: In this paper, we report the fabrication and characteristics of nano-roughened GaN laser lift-off (LLO) light-emitting diodes (LEDs) with different scale surface roughness. The surface roughness of devices was controlled by inductively coupled plasma reactive ion etching. Using this fabrication method to form nano-scaled roughness, the electrical property was almost not degraded. Furthermore, the light-output power and wall-plug efficiency of LLO LED could be both significantly enhanced about two times using this simple method
IEEE Photonics Technology Letters 07/2007; · 2.19 Impact Factor
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ABSTRACT: 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 × 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.
Semiconductor Science and Technology 06/2007; 22(7):831. · 1.72 Impact Factor
