Browsing by Author "Kuo, Cheng-Huang"

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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.
Enabling High-Injection Current Light-Emitting Diodes Prepared on 10-mu m-Thick GaN Films Grown by Hydride Vapor Phase Epitaxy
(2015-09-01)
Chen, Yu-An
;
Chang, Chia-Wei
;
Kuo, Cheng-Huang
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
In this paper, we successfully introduced the sputtered AlN/patterned sapphire substrate template into hydride vapor phase epitaxy (HVPE) using a two-step growth method. This method simplified the procedure, realized uninterrupted growth, and improved the crystal quality of GaN films. The effects of light-emitting diodes (LEDs) grown on a 10-mu m-thick GaN film through HVPE were also compared with those of the LEDs grown on a 2.4-mu m-thick GaN film through metal organic chemical vapor deposition (MOCVD). Compared with the LEDs grown on the 2.4-mu m-thick GaN film through MOCVD, the LEDs grown on the 10-mu m-thick GaN film through HVPE had significantly enhanced light output power (3.24-4.79 mW) and extended saturation current (300-355 mA). These improvements of the LEDs were attributed to the better thermal conductivities and better crystal quality of the 10-mu m-thick GaN film through HVPE than those of the 2.4-mu m-thick GaN film through MOCVD.
Functional imprinting structures on GaN-based light-emitting diodes for light pattern modulation and light extraction efficiency enhancement
(2010-07-01)
Tu, Sheng-Han
;
Wu, Shang-Yen
;
Lee, Yeeu-Chang
;
Pan, Jui-Wen
;
Kuo, Cheng-Huang
In this study, we demonstrated a simple method that can be used to simultaneously modulate the far field pattern and enhance the light extraction of GaN-based light-emitting diodes (LEDs). In this method, microstructures were imprinted on a reliable spin-on-glass surface on top of a transparent conductive layer. The far-field pattern was modulated using microoptical structures, and at the same time, the light extraction was enhanced owing to the small refractive index difference and surface roughness. There was no decrease in the electrical performance of these devices. The peak intensity shifted from 0 to 22A degrees in one-dimensional (1D) asymmetrically blazed periodic structures, and a flattened distribution with a uniform intensity within a span of 110A degrees was observed in two-dimensional (2D) symmetrically periodic structures. This method achieved 13 and 40% light enhancements for 1D and 2D structures, respectively.
GaN-Based Light-Emitting-Diode With a p-InGaN Layer
(2014-03-01)
Chen, P. H.
;
Kuo, Cheng-Huang
;
Lai, W. C.
;
Chen, Yu An
;
Chang, L. C.
GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick p-In0.01Ga0.99N layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.
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
;
Ke, Wen-Cheng
;
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.
Localized Lasing Mode in GaN Quasi-Periodic Nanopillars at Room Temperature
(2013-07-01)
Wu, Tzeng-Tsong
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Chen, Chih-Cheng
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Chen, Hao-Wen
;
Lu, Tien-Chang
;
Wang, Shing-Chung
In this paper, GaN quasi-periodic nanopillars were fabricated and investigated. The quasi-periodic nanopillars were realized by nanoimprint technique and selective area growth. Localized lasing mode was identified in the GaN quasi-periodic nanopillars. The threshold energy density and lasing wavelength were 40 mJ/cm(2) and 369 nm, respectively. The divergence angle and near-field lasing spot were measured to be 10.5 degrees and 3.6 mu m, respectively. The spontaneous emission coupling factor of localized lasing mode was estimated to be 9.4 x 10(-3). The mode patterns in the real and reciprocal spaces were calculated by the multiple scattering method to confirm the mode localization behavior.
Mode Localization in Defect-free GaN-based Bottom-up Photonic Quasicrystal Lasers
(2012)
Wu, Tzeng-Tsong
;
Chen, Chih-Cheng
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Chen, Hao-Wen
;
Lu, Tien-Chang
;
Wang, Shing-Chung
GaN-based bottom-up photonic quasicrystal (PQC) lasers were realized and characterized. Photonic quasicrystal nanopillars were realized by nanoimprint technique and selective area growth. Highly localized mode was identified for the first time in GaN-based PQC lasers. (C) 2012 Optical Society of America
Nitride-Based Blue Light-Emitting Diodes Grown With InN/GaN Matrix Quantum Wells
(2014-04-01)
Kuo, Cheng-Huang
;
Fu, Yi Keng
;
Chang, L. C.
;
Chen, Yu An
;
照明與能源光電研究所
Nitride-based light-emitting diodes (LEDs) grown with a structure of InN/GaN matrix quantum-wells (QWs) using metal-organic chemical vapor deposition are fabricated and characterized. The InN/GaN matrix QWs can significantly enhance the formation of phase-separated In-rich regions. Under an injection current of 500 A/cm(2), the LED output power can be enhanced by 26%, and the efficiency droop can be improved as compared with a conventional LED. These improvements could be attributed to the strong localization effect to remove carriers from the confining potential and capture these carriers at nonradiative centers in the active layer.
Numerical Simulation and Experimental Analysis of Current Spreading Length in Nitride-Based Light-Emitting Diodes Prepared on 10-mu m-Thick n-GaN Template
(2015-11-01)
Chen, Yu-An
;
Chang, Chia-Wei
;
Kuo, Cheng-Huang
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Numerical and experimental demonstrations were performed in this letter to enhance the current spreading length of nitride-based light-emitting diodes (LEDs) with a 10-mu m-thick n-GaN template on an AlN/high-aspect ratio patterned sapphire substrate template via hydride vapor phase epitaxy. At an injection current of 20 mA, the output powers were 4.34 and 6.39 mW for a conventional LED and an LED with a 10-mu m-thick n-GaN template, respectively. The larger LED output power is attributed to the enhanced current spreading length, which improved the heat dissipation ability and the improved crystal quality.
Optical properties of light emitting diodes with a cascading plasmonic grating
(2010-12-06)
Wang, Chih-Ming
;
Tsai, Yao-Lin
;
Tu, Sheng-Han
;
Lee, Chien-Chieh
;
Kuo, Cheng-Huang
In this paper, the polarization dependent optical properties of InGaN/GaN multi-quantum wells (MQWs) LED with cascading plasmonic gratings are investigated using an angle-resolved photoluminescence (ARPL) spectrometer. The plasmonic gratings consist of two Ag gratings with a half-pitch displacement. The ARPL spectra of the TE-TM state present a broadband emission with resonance dips occasioned by the SP resonance while the TM-TE state presents resonance peaks with low sideband emission. The resonance properties can be tuned by modifying the geometric parameters of the plasmonic grating. The ARPL spectrum of the LED sample with pure GaN 1D grating is also measured and discussed. The investigated plasmonics LED represents resonance optical properties different from the conventional surface relief LED, which can be used in special applications. (C) 2010 Optical Society of America
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
;
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
;
Kuo, Cheng-Huang
;
Chang, Li-Chuan
;
Wu, Ji-Pu
;
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.