Browsing by Author "Chang, Li-Chuan"

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Current Spreading Improvement in GaN-Based Light-Emitting Diode Grown on Nano-Rod GaN Template
(2012-04-01)
Kuo, Cheng-Huang
;
Chang, Li-Chuan
;
Chou, Hsiu-Mei
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
In this letter, we demonstrate GaN-based light-emitting diodes (LEDs) with high-quality heavily-Si-doped n-GaN prepared on a nano-rod GaN (NR-GaN) template. With 20-mA current injection, it was found that light output power (LOP) can be enhanced 29.0%, as compared to the conventional LED. Enhancement of the LOP can be attributed to the improvement of the current spreading and the increase of light extraction efficiency by using the heavily-Si-doped n-GaN prepared on the NR-GaN template.
Highly Reflective Ag/La Bilayer Ohmic Contacts to p-Type GaN
(2011)
Chen, I-Chen
;
Chen, Yi-Dar
;
Hsieh, Chih-Chien
;
Kuo, Cheng-Huang
;
Chang, Li-Chuan
A new Ag/La bilayer metal contact scheme has been developed for producing high reflectance and low contact resistivity ohmic contacts to p-GaN. An excellent reflectance of over 91% at 460 nm wavelength and low specific contact resistivity of 1.6 x 10(-4) Omega cm(2) were obtained from Ag/La (150/20 nm) contact annealed at 450 degrees C for 1 min. The La overlayer was oxidized to form La(2)O(3) when exposed to air, which effectively suppresses exposure of the Ag layer to oxygen atmosphere during annealing, leading to a good ohmic contact with smooth surface morphology and high reflectance. Additionally, Ag/La contacts show excellent thermal stability after a long thermal annealing at 300 degrees C in air ambient. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3533673] All rights reserved.
Improved light reflectance and thermal stability of Ag-based ohmic contacts on p-type GaN with La additive
(2013-05-01)
Chen, I-Chen
;
Cheng, Bo-Yuan
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Ke, Wen-Cheng
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Kuo, Cheng-Huang
;
Chang, Li-Chuan
We investigated the effect of La additive on the improvement of light reflectance and thermal stability of Ag contacts on p-GaN. A high reflectance of over 90% at 460 nm wavelength and low specific contact resistivity of 5.5 x 10(-5) Omega cm(2) were obtained from La-containing Ag contacts annealed at 300 degrees C for 1 min, which also show better thermal stability than Ag contacts after annealing in air ambient. The experimental results reveal that the addition of La could effectively slow down Ag migration in < 1 1 1 > direction during annealing, and thus suppress the Ag agglomeration at elevated temperature, leading to a good ohmic contact with improved high reflectance and thermal stability. (C) 2013 Elsevier Ltd. All rights reserved.
Output power enhancements of nitride-based light-emitting diodes with inverted pyramid sidewalls structure
(2011-02-01)
Chang, Li-Chuan
;
Kuo, Cheng-Huang
;
Kuo, Chi-Wen
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照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
This study presents nitride-based light-emitting diodes (LEDs) with inverted pyramid sidewalls by chemical wet etching nitride epitaxial layers and investigates the chemical wet etching mechanism of inverted pyramid sidewalls. It is well known that chemical etching solutions such as KOH, H(2)SO(4) and H(3)PO(4), to selectively etch the N-face GaN but not the Ga-face GaN. In this study, the N-face GaN was exposed around the chip by laser scribing at the GaN/sapphire interface. These channels provided paths for the chemical etchant to flow and allow the etching solution to further contact with and etch the exposed bottom N-face GaN. Chemical etching of the chip sidewalls formed the inverted hexagonal pyramid shape with (10-1-1) facets. Findings show that inverted pyramid sidewalls enhance 20 mA LED output power by 27% for LEDs, with chemical etching of the chip sidewalls for 4 min, compared to the conventional LED. The larger LED output power is attributed to increased light extraction efficiency by inverted pyramid sidewalls. (C) 2010 Elsevier Ltd. All rights reserved.
Regrowth of High Quality Heavily Si-Doped nGaN Utilizing Nano-Rod GaN Template
(2011)
Kuo, Cheng-Huang
;
Chang, Li-Chuan
;
Chou, Hsiu-Mei
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
In this study, heavily Si-doped n-type GaN (n-GaN) epitaxial layers with and without nanorod GaN (NR GaN) template were grown by metal organic chemical vapor deposition (MOCVD) system. It was found that we could achieve high-qulaity heavily Si-doped n-GaN layers by using the NR GaN template. It was also found that we can reduce etching pits density in n-GaN (1.5E19 cm(-3)) epitaxial layer by a factor of 2.82 using the NR GaN template, as compared to the conventional sapphire substrate. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3617533] All rights reserved.
Spatial Correlation Between Efficiency and Crystal Structure in GaN-Based Light-Emitting Diodes Prepared on High-Aspect Ratio Patterned Sapphire Substrate With Sputtered AlN Nucleation Layer
(2014-07-01)
Chang, Li-Chuan
;
Chen, Yu-An
;
Kuo, Cheng-Huang
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
In this paper, we investigate sputtered physical vapor deposition (PVD) AlN nucleation layer effects on crystal quality and efficiency of GaN-based light-emitting diodes (LEDs) prepared on high-aspect ratio patterned sapphire substrate (HARPSS). The crystal quality of the GaN epitaxial layer prepared on HARPSS with a PVD AlN nucleation layer was significantly better than that with a conventional metal organic chemical vapor deposition (MOCVD)-grown AlN nucleation layer. In addition, the pure wurzite structure GaN prepared on HARPSS could be obtained using PVD AlN nucleation layer. With the PVD AlN nucleation layer, the 20-mA LED light output power of the LEDs can be enhanced by 47.7% compared with the LEDs with the conventional MOCVD-grown AlN nucleation layer.
Void Shapes Controlled by Using Interruption-Free Epitaxial Lateral Overgrowth of GaN Films on Patterned SiO2 AlN/Sapphire Template
(2014)
Chen, Yu-An
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Kuo, Cheng-Huang
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Chang, Li-Chuan
;
Wu, Ji-Pu
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照明與能源光電研究所
GaN epitaxial layers with embedded air voids grown on patterned SiO2 AlN/sapphire templates were proposed. Using interruption-free epitaxial lateral overgrowth technology, we realized uninterrupted growth and controlled the shape of embedded air voids. These layers showed improved crystal quality using X-ray diffraction and measurement of etching pits density. Compared with conventional undoped-GaN film, the full width at half-maximum of the GaN (0 0 2) and (1 0 2) peaks decreased from 485 arcsec to 376 arcsec and from 600 arcsec to 322 arcsec, respectively. Transmission electron microscopy results showed that the coalesced GaN growth led to bending threading dislocation. We also proposed a growth model based on results of scanning electron microscopy.