Browsing by Author "Lee, Ming-Lun"

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Improved Output Power of InGaN LEDs by Lateral Overgrowth on Si-Implanted n-GaN Surface to Form Air Gaps
(2012-08-01)
Tu, Shang-Ju
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Lee, Ming-Lun
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Yeh, Yu-Hsiang
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Huang, Feng-Wen
;
Chen, Po-Cheng
"In this paper, air gaps were embedded in the n-GaN layer to improve light output power of InGaN-based light-emitting diodes (LEDs). Si ions (Si+28) were implanted on the n-GaN surface, causing a lattice constant disorder. Therefore, the GaN grown on the Si-implanted areas had a lower growth rate than the implantation-free regions. Without using a dielectric thin film, lateral epitaxial overgrowth technique was used to form air gaps above the implanted regions and below the active layers of InGaN LEDs. We proposed the growth mechanisms of GaN layer on the Si-implanted GaN templates and characterized the InGaN-based LEDs with embedded air gaps array. With a 20-mA current injection, experimental results indicate that light output power (LOP) of the proposed LEDs was enhanced by 36%, compared with those of the conventional LEDs. This enhancement can be attributed to the light scattering at the textured GaN/gap interfaces to increase the effective light escape cone in the LEDs. Based on ray tracing simulation, if the height and the width of bottom of gaps were increased to 3 mu m, the Lop could be enhanced over 70%."
Influence of patterned sapphire substrates with different symmetry on the light output power of InGaN-based LEDs
(2014-11-03)
You, Yao-Hong
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Su, Vin-Cent
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Ho, Ti-En
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Lin, Bo-Wen
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Lee, Ming-Lun
This paper aims to investigate the light output power (LOP) of InGaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) with different symmetry. The GaN epitaxial layers grown on the hexagonal lattice arrangement PSS (HLAPSS) have a lower compressive strain than the ones grown on the square lattice arrangement PSS (SLAPSS). The quantum-confined Stark effect (QCSE) is also affected by the residual compressive strain. Based on the experimentally measured data and the ray tracing simulation results, the InGaN-based LED with the HLAPSS has a higher LOP than the one with the SLAPSS due to the weaker QCSE within multiple-quantum wells (MQWs).
Linear photon up-conversion of 450 meV in InGaN/GaN multiple quantum wells via Mn-doped GaN intermediate band photodetection
(2011-11-07)
Huang, Feng-Wen
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Sheu, Jinn-Kong
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Lee, Ming-Lun
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Tu, Shang-Ju
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Lai, Wei-Chih
Up-converted heterostructures with a Mn-doped GaN intermediate band photodetection layer and an InGaN/GaN multiple quantum well (MQW) luminescence layer grown by metal-organic vapor-phase epitaxy are demonstrated. The up-converters exhibit a significant up-converted photoluminescence (UPL) signal. Power-dependent UPL and spectral responses indicate that the UPL emission is due to photo-carrier injection from the Mn-doped GaN layer into InGaN/GaN MQWs. Photons convert from 2.54 to 2.99 eV via a single-photon absorption process to exhibit a linear up-conversion photon energy of similar to 450 meV without applying bias voltage. Therefore, the up-conversion process could be interpreted within the uncomplicated energy level model. (C) 2011 Optical Society of America
Non-alloyed Cr/Au Ohmic contacts to N-face and Ga-face n-GaN
(2012-03-05)
Yan, Liang-Jyi
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Kuo, Cheng Huang
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Sheu, Jinn-Kong
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Lee, Ming-Lun
;
Tseng, Wei-Chun
Non-alloyed Cr/Au Ohmic contacts on N-face and Ga-face n-GaN were studied. The specific contact resistances (rho(c)) of Cr/Au contacts onto the N-face and Ga-face n-GaN were as low as 2.4 x 10 (4) Omega cm(2) and 2.4 x 10(-5) Omega cm(2), respectively. Native oxide formed on the n-GaN surface was believed to be the key factor for higher rho(c). The results of X-ray photoelectron spectroscopy confirmed that n-GaN samples with different surface polarities or treated by different chemical solutions exhibited significant differences in gallium oxide content on the surface, which led to a marked difference in the rho(c) of non-alloyed Cr/Au Ohmic contacts to GaN films. (C) 2011 Elsevier B.V. All rights reserved.
Optical properties of Mn in regrown GaN-based epitaxial layers
(2012-04-01)
Huang, Feng-Wen
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Sheu, Jinn-Kong
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Tu, Shang-Ju
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Chen, Po-Cheng
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Yeh, Yu-Hsiang
The memory effect and redistribution of manganese (Mn) into subsequently regrown GaN-based epitaxial layers by metalorganic chemical vapor deposition were revealed. Low-temperature up-converted photoluminescence (UPL) and the secondary ion mass spectrometry were performed on GaN-based epitaxial samples with and without Mn doping to study the effect of residual Mn on optical property. UPL emission, which originated from residual Mn doping in regrown InGaN quantum wells (QWs) because of the memory effect of the reactor, could be eliminated in an air-exposed and H-2-baking manner prior to the regrowth of the QWs. Considerable residual Mn background level and slow decay rate of Mn concentration tail were also observed in the regrown epitaxial layers, which could be attributed to the memory effect or surface segregation and diffusion from the Mn-doped underlying layer during regrowth in the Mn-free reactor. (C) 2012 Optical Society of America
The Analysis of Nano-Patterned Sapphire Substrates-Induced Compressive Strain to Enhance Quantum-Confined Stark Effect of InGaN-Based Light-Emitting Diodes
(2013-01-01)
Chen, Po-Hsun
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Su, Vincent
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You, Yao-Hong
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Lee, Ming-Lun
;
Hsieh, Cheng-Ju
This paper demonstrates that the quantum-confined stark effect of InGaN-based light-emitting diodes can be enhanced by the means of using the hexagonal nano-post patterned sapphire substrates based on the increase of the post-duty cycle.