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Advances in Quantum-Dot-Based Displays
(2020-07-01)
Huang, Yu-Ming
;
Singh, Konthoujam James
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Liu, An-Chen
;
Lin, Chien-Chung
;
Chen, Zhong
In terms of their use in displays, quantum dots (QDs) exhibit several advantages, including high illumination efficiency and color rendering, low-cost, and capacity for mass production. Furthermore, they are environmentally friendly. Excellent luminescence and charge transport properties of QDs led to their application in QD-based light-emitting diodes (LEDs), which have attracted considerable attention in display and solid-state lighting applications. In this review, we discuss the applications of QDs which are used on color conversion filter that exhibit high efficiency in white LEDs, full-color micro-LED devices, and liquid-type structure devices, among others. Furthermore, we discuss different QD printing processes and coating methods to achieve the full-color micro-LED. With the rise in popularity of wearable and see-through red, green, and blue (RGB) full-color displays, the flexible substrate is considered as a good potential candidate. The anisotropic conductive film method provides a small controllable linewidth of electrically conductive particles. Finally, we discuss the advanced application for flexible full-color and highly efficient QD micro-LEDs. The general conclusion of this study also involves the demand for a more straightforward QD deposition technique, whose breakthrough is expected.
Particular Failure Mechanism of GaN-Based Alternating Current Light-Emitting Diode Induced by GaOx Oxidation
(2010-08-01)
Yen, Hsi-Hsuan
;
Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
;
光電工程研究所
This investigation describes the unique failure mechanism of the Wheatstone bridge circuit-type alternating current light-emitting diode (WB AC-LED). The micro-LEDs in WB AC-LED rectifying branches were reverse biased, and therefore, positive charges (holes) accumulated in the n-type GaN layer under the active region and combined with the GaN material and OH- ions to generate GaOx oxidation grains. The GaOx generation speed was fast with high reverse voltage applied to micro-LEDs, and the expansion of GaOx dimensions degraded the opto-electrical characteristics and eventually caused failure of the WB AC-LED. The root-mean-square reverse voltage dropped across each micro-LED from -13.1 to -6.7 V with different micro-LEDs array arrangements extended the WB AC-LED life-time from being less than 650 h to more than 1600 h, respectively.
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
;
Hsieh, Dan-Hua
;
Hong, Kuo-Bin
;
Lin, Da-Wei
;
Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.
Wide-Range Correlated Color Temperature Light Generation From Resonant Cavity Hybrid Quantum Dot Light-Emitting Diodes
(2015-07-01)
Chen, Kuo-Ju
;
Lin, Chien-Chung
;
Han, Hau-Vei
;
Lee, Chia-Yu
;
Chien, Shih-Hsuan
This study presents extremely uniform colloidal quantum dot white light-emitting diodes (QD-WLEDs) that demonstrate a high color rendering index (CRI) and correlated color temperatures (CCTs) ranging from 2500 to 4500 K. Experimental results indicate that the structure of the distributed Bragg reflector (DBR) containing a stopband in the UV region enhances the intensity output of both monochromatic QD-LEDs and QD-WLEDs by reflecting the unconverted UV light back onto the package to excite the QDs further. Furthermore, the angular CCT uniformity of the QD-WLEDs also improved considerably because of the dependence of the DBR structure on the incident angle. The angular CCT deviation in the range of -70 degrees to 70 degrees decreased to 39 K and the CRI of the WLED is higher than 90. The high-CRI and uniform angular CCT QD-WLED containing the DBR demonstrates potential applicability as the lighting source of next-generation display devices and solid-state lighting.
Structural Effects on Highly Directional Far-Field Emission Patterns of GaN-Based Micro-Cavity Light-Emitting Diodes With Photonic Crystals
(2010-10-01)
Lai, Chun-Feng
;
Kuo, Hao-Chung
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Chao, Chia-Hsin
;
Yu, Peichen
;
Yeh, Wen-Yung
This study theoretically and experimentally investigates the highly directional far-field emission patterns of GaN photonic crystal (PhC) micro-cavity light-emitting diodes (MCLEDs) depending on varying structural parameters. Angular-spectra-resolved electroluminescence measurements reveals the behavior of guided-mode extraction which is significantly affected by the structural parameters of GaN PhC MCLEDs, where the GaN cavity thickness decides the extracted guided mode numbers, PhC lattice constant influences the distribution of far-field emission, and PhC hole depth affects the interaction with guided modes. The proposed GaN ultrathin MCLED (uMCLED) with PhC lattice constant of 420 nm and deep hole depth of 250 nm exhibited a maximum output light extraction efficiency of 248% under one-watt input power compared to GaN non-PhC uMCLED and produced a directional far-field emission pattern at half intensity near +/- 17 degrees. The present results indicate that highly directional light extraction enhancement could contribute to developments of many applications, especially for etendue-limited applications such as pico-projectors.
High-Efficiency and Crack-Free InGaN-Based LEDs on a 6-inch Si (111) Substrate With a Composite Buffer Layer Structure and Quaternary Superlattices Electron-Blocking Layers
(2014-05-01)
Li, Zhen-Yu
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Lee, Chia-Yu
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Lin, Da-Wei
;
Lin, Bing-Cheng
;
Shen, Kun-Ching
In this paper, a composite buffer layer structure (CBLS) with multiple AlGaN layers and grading of Al composition/u-GaN1/(AlN/GaN) superlattices/u-GaN2 and InAlGaN/AlGaN quaternary superlattices electron-blocking layers (QSLs-EBLs) are introduced into the epitaxial growth of InGaN-based light-emitting diodes (LEDs) on 6-inch Si (111) substrates to suppress cracking and improve the crystalline quality and emission efficiency. The effect of CBLS and QSLs-EBL on the crystalline quality and emission efficiency of InGaN-based LEDs on Si substrates was studied in detail. Optical microscopic images revealed the absence of cracks and Ga melt-back etching. The atomic force microscopy images exhibited that the root-meansquare value of the surface morphology was only 0.82 nm. The full widths at half maxima of the (0002) and (1012) reflections in the double crystal X-ray rocking curve were similar to 330 and 450 arcs, respectively. The total threading dislocation density, revealed by transmission electron microscopy, was <6 x 10(8) cm(-2). From the material characterizations, described above, blue and white LEDs emitters were fabricated using the epiwafers of InGaNbased LEDs on 6-inch Si substrates. The blue LEDs emitter that comprised blue LEDs chip and clear lenses had an emission power of 490 mW at 350 mA, a wall-plug efficiency of 45% at 350 mA, and an efficiency droop of 80%. The white LEDs emitter that comprised blue LEDs chip and yellow phosphor had an emission efficiency of similar to 110 lm/W at 350 mA and an efficiency droop of 78%. These results imply that the use of a CBLS and QSLs-EBL was found to be very simple and effective in fabricating high-efficiency InGaN-based LEDs on Si for solid-state lighting applications.
Investigation and Comparison of the GaN-Based Light-Emitting Diodes Grown on High Aspect Ratio Nano-Cone and General Micro-Cone Patterned Sapphire Substrate
(2013-12-01)
Huang, Jhih-Kai
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Lin, Da-Wei
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Shih, Min-Hsiung
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Lee, Kang-Yuan
;
Chen, Jyun-Rong
In this paper, we demonstrated the high performance GaN-based LEDs by using a high aspect ratio cone-shape nano-patterned sapphire substrate (HAR-NPSS). We utilized nano-imprint lithography (NIL) and dry-etching system to fabricate a high depth HAR-NPSS. The micro-scale patterned sapphire substrate (PSS) was also used for comparison. A great enhancement of light output was observed when GaN-based LEDs were grown on a HAR-NPSS or a PSS. The light output power of LEDs with a HAR-NPSS and LEDs with a PSS were enhanced of 49 and 38% compared to LEDs with a unpatterned sapphire substrate. The high output power of the LED with a HAR-NPSS indicated that the technology of NAR-NPSS not only can improve the crystalline quality of GaN-based LEDs but also a promising development to a NPSS.
An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure
(2013-11-01)
Chen, Kuo-Ju
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Chen, Hsin-Chu
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Lin, Chien-Chung
;
Wang, Chao-Hsun
;
Yeh, Chia-Chi
An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a (c) nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.
Improving the Angular Color Uniformity of Hybrid Phosphor Structures in White Light-Emitting Diodes
(2013-10-01)
Chen, Kuo-Ju
;
Han, Hau-Vei
;
Lin, Bing-Cheng
;
Chen, Hsin-Chu
;
Shih, Min-Hsiung
This letter examines a hybrid phosphor structure for white light-emitting diodes. The hybrid phosphor structure produces more efficient luminosity and more uniform angular correlated color temperature (CCT) than the conventional dispensing method. The experimental results show that the CCT deviation improved from 453 to 280 K between -70 degrees and 70 degrees. This was likely caused by the large blue light divergent angle. The lumen output produced was higher than that produced by dispense and conformal phosphor structures. Therefore, the results show that the hybrid phosphor structure can be used in solid-state lighting.
Reduction of Efficiency Droop in InGaN Light-Emitting Diode Grown on Self-Separated Freestanding GaN Substrates
(2011-06-15)
Chao, Chu-Li
;
Xuan, Rong
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Yen, Hsi-Hsuan
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Chiu, Ching-Hsueh
;
Fang, Yen-Hsiang
Using a GaN nanorod template in a hydride vapor phase epitaxy (HVPE) system can manufacture a freestanding GaN (FS-GaN) substrate with threading dislocation densities down to similar to 10(7) cm(-2). In this letter, we report InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on this FS-GaN substrate. The defect densities in the homoepitaxially grown LEDs were substantially reduced, leading to improved light emission efficiency. Compared with the LED grown on sapphire, we obtained a lower forward voltage, smaller diode ideality factor, and higher light-output power in the same structure grown on FS-GaN. The external quantum efficiency (EQE) of LEDs grown on FS-GaN were improved especially at high injection current, which brought the efficiency droop phenomenon greatly reduced at high current density.

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