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Crystals
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GaN-Based Optoelectronic Materials and Light Emitting Devices
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GaN-Based Optoelectronic Materials and Light Emitting Devices

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 75108

Special Issue Editors

Prof. Dr. Hao-Chung Kuo

E-Mail Website
Guest Editor
Department of Photonics, College of Electrical and Computer Engineering, National Chiao Tung University, 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan
Interests: nanostructured optoelectronic materials and devices; III-V (nitride) high speed semiconductor laser technology and related research
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Ke Xu

E-Mail Website
Guest Editor
Chinese Academy of Sciences, Suzhou Institute of Nano-Tech and Nano-Bionics, Beijing, China
Interests: GaN free standing substrate
Prof. Dr. Zhaojun Liu

E-Mail Website
Guest Editor
Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Qingshuihe, Shenzhen, China
Interests: micro-LEDs; advanced displays and AR/VR; mass transferring and advanced packaging; GaN transistors and LEDs; wearable devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

GaN is an excellent material for making optoelectronic devices. Global sales of GaN-based blue, green and white LEDs are netting billions of dollars every year, and there is also a substantial market for in-plane lasers emitting in the blue, blue-violet and green. Vertical-cavity surface-emitting lasers (VCSELs) have many advantages such as small footprint, circular symmetry of output beam, two-dimensional scalability and/or addressability, surface-mount packaging, good price-performance ratio, and simple optics/alignment for output coupling. In this Special Issue, we would like to invite all papers related light sources in many applications, including optical storage, laser printers, projectors, displays, solid-state lighting, optical communications and biosensors. Especially, in the following fields:

  • Novel LED or laser material and device from UV to green emission
  • Green laser or VCSEL for micro-projector
  • Micro-LED for micro-display application and other potential application like LiFi, Bio-application, etc.
  • Microcavity and nanolaser based on GaN material

Prof. Dr. Hao-chung Kuo
Prof. Dr. Ke Xu
Prof. Dr. Zhaojun Liu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • LED
  • microdisplay
  • UV
  • Green
  • Laser
  • Light source
  • LiFi
  • Free standing substarte

Published Papers (17 papers)

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Research

12 pages, 3829 KiB  
Article
The Study of High Breakdown Voltage Vertical GaN-on-GaN p-i-n Diode with Modified Mesa Structure
by Wen-Chieh Ho, Yao-Hsing Liu, Wen-Hsuan Wu, Sung-Wen Huang Chen, Jerry Tzou, Hao-Chung Kuo and Chia-Wei Sun
Crystals 2020, 10(8), 712; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10080712 - 18 Aug 2020
Cited by 4 | Viewed by 4530
Abstract
In this paper, we fabricated Gallium Nitride (GaN) vertical p-i-n diodes grown on free-standing GaN (FS-GaN) substrates. This homogeneous epitaxy led to thicker GaN epi-layers grown on the FS-GaN substrate, but a high crystalline quality was maintained. The vertical [...] Read more.
In this paper, we fabricated Gallium Nitride (GaN) vertical p-i-n diodes grown on free-standing GaN (FS-GaN) substrates. This homogeneous epitaxy led to thicker GaN epi-layers grown on the FS-GaN substrate, but a high crystalline quality was maintained. The vertical GaN p-i-n diode showed a low specific on-resistance of 0.85 mΩ-cm2 and high breakdown voltage (BV) of 2.98 kV. The high breakdown voltage can be attributed to the thick GaN epi-layer and corresponds to the mesa structure. Improvement of the device characteristics by the mesa structure was investigated using device simulations. We proved that a deeper mesa depth is able to decrease the electric field at the bottom of the mesa structure. Furthermore, a smaller mesa bevel angle will assist the BV up to 2.98 kV at a 60° bevel angle. Our approach demonstrates structural optimization of GaN vertical p-i-n diodes is useful to improve the device performance. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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12 pages, 1890 KiB  
Article
Optical Characterization of GaN-Based Vertical Blue Light-Emitting Diodes on P-Type Silicon Substrate
by Yu Lei, Hui Wan, Bin Tang, Shuyu Lan, Jiahao Miao, Zehong Wan, Yingce Liu and Shengjun Zhou
Crystals 2020, 10(7), 621; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10070621 - 16 Jul 2020
Cited by 4 | Viewed by 4501
Abstract
Fabricating GaN-based light-emitting diodes (LEDs) on a silicon (Si) substrate, which is compatible with the widely employed complementary metal–oxide–semiconductor (CMOS) circuits, is extremely important for next-generation high-performance electroluminescence devices. We conducted a systematic investigation of the optical properties of vertical LEDs, to reveal [...] Read more.
Fabricating GaN-based light-emitting diodes (LEDs) on a silicon (Si) substrate, which is compatible with the widely employed complementary metal–oxide–semiconductor (CMOS) circuits, is extremely important for next-generation high-performance electroluminescence devices. We conducted a systematic investigation of the optical properties of vertical LEDs, to reveal the impacts of the manufacturing process on their optical characteristics. Here, we fabricated and characterized high-efficiency GaN-based LEDs with integrated surface textures including micro-scale periodic hemispherical dimples and nano-scale random hexagonal pyramids on a 4 inch p-type Si substrate. The highly reflective Ag/TiW metallization scheme was performed to decrease downward-absorbing light. We demonstrated the influence of transferring LED epilayers from a sapphire substrate onto the Si substrate on the emission characteristics of the vertical LEDs. The removal of the sapphire substrate reduced the adverse impacts of the quantum-confined Stark effect (QCSE). The influence of integrated surface textures on the light extraction efficiency (LEE) of the vertical LEDs was studied. With the injection current of 350 mA, vertical LEDs with integrated surface textures demonstrated an excellent light output power of 468.9 mW with an emission peak wavelength of 456 nm. This work contributes to the integration of GaN-based vertical LEDs into Si-based integrated circuits. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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15 pages, 9571 KiB  
Article
Improving the Power Efficiency of Micro-LED Displays with Optimized LED Chip Sizes
by En-Lin Hsiang, Ziqian He, Yuge Huang, Fangwang Gou, Yi-Fen Lan and Shin-Tson Wu
Crystals 2020, 10(6), 494; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10060494 - 08 Jun 2020
Cited by 40 | Viewed by 8530
Abstract
Micro-LED (light-emitting diode) is a potentially disruptive display technology, while power consumption is a critical issue for all display devices. In this paper, we develop a physical model to evaluate the power consumption of micro-LED displays under different ambient lighting conditions. Both power [...] Read more.
Micro-LED (light-emitting diode) is a potentially disruptive display technology, while power consumption is a critical issue for all display devices. In this paper, we develop a physical model to evaluate the power consumption of micro-LED displays under different ambient lighting conditions. Both power efficiency and ambient reflectance are investigated in two types of full color display structures: red/green/blue (RGB) micro-LEDs, and blue-LED pumped quantum dots color-conversion. For each type of display with uniform RGB chip size, our simulation results indicate that there exists an optimal LED chip size, which leads to 30–40% power saving. We then extend our model to analyze different RGB chip sizes, and find that with optimized chip sizes an additional 12% average power saving can be achieved over that with uniform chip size. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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10 pages, 3067 KiB  
Article
Design and Simulation of Low Circadian Action Micro-LED Displays with Four Primary Colors
by Ziqian He, Guanjun Tan, Yi-Fen Lan and Shin-Tson Wu
Crystals 2020, 10(5), 383; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10050383 - 08 May 2020
Cited by 3 | Viewed by 4306
Abstract
Nowadays, displays are ubiquitous in our daily lives. Long-time exposure to a display’s unnatural light could influence the user’s circadian rhythm, especially at night. Here, we propose a four-color micro-light-emitting diode (LED) display to achieve low circadian action for nighttime uses. Specifically, we [...] Read more.
Nowadays, displays are ubiquitous in our daily lives. Long-time exposure to a display’s unnatural light could influence the user’s circadian rhythm, especially at night. Here, we propose a four-color micro-light-emitting diode (LED) display to achieve low circadian action for nighttime uses. Specifically, we evaluate the RGBW-type (red, green, blue, and white) and RYGB-type (red, yellow, green, and blue) micro-LED displays in terms of circadian effect and color gamut coverage. With the addition of an extra white subpixel, it was found that the circadian effect at night can be reduced dramatically, but the color gamut remains unchanged. However, with an additional yellow subpixel, both the circadian effect and color gamut were found to improve. Finally, we simulated the circadian illuminance of real image contents for different displays. In comparison with existing liquid crystal displays, organic LED displays, and RGB (red, green, blue) micro-LED displays, the proposed four-primary-color micro-LED displays can significantly reduce the circadian effect at night. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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10 pages, 3371 KiB  
Article
Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes
by Shuo-Wei Chen, Chia-Jui Chang and Tien-Chang Lu
Crystals 2020, 10(4), 311; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10040311 - 17 Apr 2020
Cited by 6 | Viewed by 4330
Abstract
Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different [...] Read more.
Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different thickness of n-type GaN layers by using cathodoluminescence (CL), microphotoluminescence (PL), and depth-resolved confocal Raman spectroscopy. The results indicated that V-pits formation situation can be analyzed using CL. From the emission peak intensity ratio of prestrained layers and multiple quantum wells (MQWs) in the CL spectrum, information regarding strain relaxation between prestrained layers and MQWs was determined. Furthermore, micro-PL and depth-resolved confocal Raman spectroscopy were employed to validate the results obtained from CL measurements. The growth conditions of prestrained layers played a dominant role in the determination of LED performance. The benefit of the thick layer of n-GaN was the strain reduction, which was counteracted by an increase in light absorption in thick n-type doped layers. Consequently, the most satisfactory LED performance was observed in a structure with relatively lower growth temperature of prestrained layers that exhibited larger V-pits, leading to higher strain relaxation and thinner n-type GaN layers, which prevent light absorption caused by n-type GaN layers. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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12 pages, 4064 KiB  
Article
The Photothermal Stability Study of Quantum Dots Embedded in Sodium Chlorides
by Yu-Ming Huang, Shun-Chieh Hsu, Ning Li, Chung-Ping Yu, Li-Ann Ke, Chung-Ping Huang, Shu-Hsiu Chang, Yu-Lun Chueh, Hao-Chung Kuo and Chien-Chung Lin
Crystals 2020, 10(1), 2; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10010002 - 18 Dec 2019
Cited by 1 | Viewed by 2955
Abstract
An efficient and useful method for the incorporation of colloidal quantum dots (QDs) into ionic matrices is demonstrated. We prepared three different synthesis methods, which are traditional saturated-salt water, methanol-assisted, and ethanol-assisted methods. The continuous thermal and photonic stress tests indicate that the [...] Read more.
An efficient and useful method for the incorporation of colloidal quantum dots (QDs) into ionic matrices is demonstrated. We prepared three different synthesis methods, which are traditional saturated-salt water, methanol-assisted, and ethanol-assisted methods. The continuous thermal and photonic stress tests indicate that the high temperature, instead of photonic excitation stress, is more detrimental to the illumination capability of the quantum dots. While the traditional saturated-salt water synthesis and methanol-assisted method are quite effective in low temperature and low photon excitation intensity, the quantum dots sealed by the ethanol-assisted method cannot hold under all conditions. An over-1000-h aging test can provide crucial information for the longevity of these quantum dots, and more than 10,000 h of lifetime can be expected. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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9 pages, 2106 KiB  
Article
A Novel Liquid Packaging Structure of Deep-Ultraviolet Light-Emitting Diodes to Enhance the Light-Extraction Efficiency
by Chieh-Yu Kang, Chih-Hao Lin, Tingzhu Wu, Po-Tsung Lee, Zhong Chen and Hao-Chung Kuo
Crystals 2019, 9(4), 203; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9040203 - 12 Apr 2019
Cited by 19 | Viewed by 4315
Abstract
To realize high-efficiency, AlGaN-based, deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency and reducing thermal resistance is very crucial. We proposed a liquid packaging structure that could enhance optical power by 27.2% and 70.7% for flat type and lens type 281-nm DUV-LEDs, respectively. [...] Read more.
To realize high-efficiency, AlGaN-based, deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency and reducing thermal resistance is very crucial. We proposed a liquid packaging structure that could enhance optical power by 27.2% and 70.7% for flat type and lens type 281-nm DUV-LEDs, respectively. A significant improvement effect at different wavelengths, such as 268 nm and 310 nm, was also observed. Furthermore, using the liquid packaging structure, the thermal resistance was reduced by 30.3% compared to the conventional structure. Finally, the reliability of liquid packaging DUV-LEDs was tested. The light output maintenance of liquid packaging DUV-LEDs was compared to the conventional structure. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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9 pages, 8552 KiB  
Article
Ultra-High Light Extraction Efficiency and Ultra-Thin Mini-LED Solution by Freeform Surface Chip Scale Package Array
by Che-Hsuan Huang, Chieh-Yu Kang, Shu-Hsiu Chang, Chih-Hao Lin, Chun-Yu Lin, Tingzhu Wu, Chin-Wei Sher, Chien-Chung Lin, Po-Tsung Lee and Hao-Chung Kuo
Crystals 2019, 9(4), 202; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9040202 - 11 Apr 2019
Cited by 21 | Viewed by 5269
Abstract
In this study, we present a novel type of package, freeform-designed chip scale package (FDCSP), which has ultra-high light extraction efficiency and bat-wing light field. For the backlight application, mainstream solutions are chip-scale package (CSP) and surface-mount device package (SMD). Comparing with these [...] Read more.
In this study, we present a novel type of package, freeform-designed chip scale package (FDCSP), which has ultra-high light extraction efficiency and bat-wing light field. For the backlight application, mainstream solutions are chip-scale package (CSP) and surface-mount device package (SMD). Comparing with these two mainstream types of package, the light extraction efficiency of CSP, SMD, and FDCSP are 88%, 60%, and 96%, respectively. In addition to ultra-high light extraction efficiency, because of the 160-degree bat-wing light field, FDCSP could provide a thinner and low power consumption mini-LED solution with a smaller number of LEDs than CSP and SMD light source array. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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7 pages, 3021 KiB  
Article
Design and Fabrication of the Reliable GaN Based Vertical-Cavity Surface-Emitting Laser via Tunnel Junction
by Chih-Chiang Shen, Yun-Ting Lu, Yen-Wei Yeh, Cheng-Yuan Chen, Yu-Tzu Chen, Chin-Wei Sher, Po-Tsung Lee, Ya-Hsuan Shih, Tien-Chang Lu, Tingzhu Wu, Ching-Hsueh Chiu and Hao-Chung Kuo
Crystals 2019, 9(4), 187; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9040187 - 01 Apr 2019
Cited by 15 | Viewed by 4234
Abstract
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of [...] Read more.
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of the VCSEL with TJ structure was much smaller than that of the VCSEL with an Indium-Tin-Oxide (ITO) layer. We have been demonstrated that laser output performance is improved by using the TJ structure when compared to the typical VCSEL structure of the ITO layer. The output power obtained at 2.1 mW was enhanced by a factor of 3.5 by the successful reduction of threshold current density (Jth) from 12 to 8.5 kA/cm2, and the enlarged slope efficiency was due to less absorption in VCSEL with a TJ structure. Finally, the samples passed the high temperature (70 °C) and high operation current (1.5 × Jth) test for over 500 h. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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8 pages, 4700 KiB  
Article
Deep Etched Gallium Nitride Waveguide for Raman Spectroscopic Applications
by Yu-Li Hsieh, Wen-Shao Chen, Liann-Be Chang, Lee Chow, Samuel Borges, Jr., Alfons Schulte, Shiang-Fu Huang, Ming-Jer Jeng and Chih-Jen Yu
Crystals 2019, 9(3), 176; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9030176 - 26 Mar 2019
Cited by 2 | Viewed by 3611
Abstract
Gallium nitride (GaN) materials with a high chemical stability and biocompatibility are well suited for bio-sensing applications and evanescent wave spectroscopy. However, GaN poses challenges for processing, especially for deep etching using conventional etching techniques. Here, we present a dry-etching technique using tetraethyl [...] Read more.
Gallium nitride (GaN) materials with a high chemical stability and biocompatibility are well suited for bio-sensing applications and evanescent wave spectroscopy. However, GaN poses challenges for processing, especially for deep etching using conventional etching techniques. Here, we present a dry-etching technique using tetraethyl orthosilicate (TEOS) oxide as an etching barrier. We demonstrate that a sharp, vertically-etched waveguide pattern can be obtained with low surface roughness. The fabricated GaN waveguide structure is further characterized using field-emission scanning electron microscopy, Raman spectroscopy, and a stylus profilometer. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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10 pages, 6108 KiB  
Article
A Light Guide Plate That Uses Asymmetric Intensity Distribution of Mini-LEDs for the Planar Illuminator
by Zhi-Ting Ye, Yung-Min Pai, Cheng-Huan Chen, Hao-Chung Kuo and Lung-Chien Chen
Crystals 2019, 9(3), 141; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9030141 - 08 Mar 2019
Cited by 11 | Viewed by 4033
Abstract
Traditional backlights are designed with new dot patterns, and then injection molding, laser beam fabrication, or UV (Ultraviolet) roll-to-plate imprinting is used to apply dot patterns to a light guide plate—the process consumes considerable time and resources. Therefore, we propose a novel light [...] Read more.
Traditional backlights are designed with new dot patterns, and then injection molding, laser beam fabrication, or UV (Ultraviolet) roll-to-plate imprinting is used to apply dot patterns to a light guide plate—the process consumes considerable time and resources. Therefore, we propose a novel light guide design that does not use a dot pattern. We designed an asymmetric intensity distribution of mini-LEDs (Light Emitting Diode) and a light guide plate with a fully printed diffusion reflection on the bottom surface for a planar illuminator. The design rules for the proposed architecture are described in this paper. The archetype design with a 152.4 mm circular down-light has a diameter of 143 mm for the planar light source module. The experiment achieved a total efficiency of 85% and uniformity of 92.6%. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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11 pages, 9747 KiB  
Article
Bird-Wing Optical-Reflector Design with Photocatalyst for Low-Glare Mosquito Trapping System with Light-Emitting Diodes
by Wei-Hsiung Tseng, Diana Juan, Wei-Cheng Hsiao, Yi Chian Chen, Cheng-Han Chan, Hsin-Yi Ma and Hsiao-Yi Lee
Crystals 2019, 9(3), 139; https://doi.org/10.3390/cryst9030139 - 07 Mar 2019
Cited by 1 | Viewed by 2625
Abstract
Dengue fever is the most serious vector-borne disease in Asia. There are still no dengue vaccines or therapeutic drugs, and vector-mosquito control is the main prevention and treatment method. The prevention and control of dengue-fever vector mosquitoes in Taiwan is still dominated by [...] Read more.
Dengue fever is the most serious vector-borne disease in Asia. There are still no dengue vaccines or therapeutic drugs, and vector-mosquito control is the main prevention and treatment method. The prevention and control of dengue-fever vector mosquitoes in Taiwan is still dominated by larval control. However, the removal of the source of mosquito-borne diseases has not been fully implemented, and the removal process of vector-borne mosquitoes cannot keep up with their breeding rate. In addition, chemical agents used in the elimination of pathogenic mosquitoes may cause mosquito resistance and environmental pollution. Therefore, it is important to develop new prevention and control technologies. This study is dedicated to the development of a mosquito trapping optical system with high efficiency and low glare that is safe for humans. The system is mainly equipped with ultraviolet light-emitting diodes (UV-LED), a freeform-surfaced optical reflector, and a photocatalyst. The reflector can lead light downward for the protection of user eyes, and expand the range of trapping mosquitoes to 225 π m2. Based on practical experiments, captured mosquitoes increased by about 450% through the proposed system compared to conventional traps using UV LED. In addition, the proposed system is shown to be 45% more enhanced in trapping capability after a photocatalyst (titanium dioxide) coating is applied to its reflector. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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9 pages, 3977 KiB  
Article
Square Column Structure of High Efficiency, Reliable, Uniformly Flexible LED Devices
by Chih-Hao Lin, Yung-Min Pai, Chieh-Yu Kang, Huang-Yu Lin, Chun-Fu Lee, Xin-Yin Chen, Hsien-Hao Tu, Jin-Jia Yang, Cheng-Huan Chen, Chien-Chung Lin, Po-Tsung Lee, Chin-Wei Sher and Hao-Chung Kuo
Crystals 2018, 8(12), 472; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst8120472 - 16 Dec 2018
Cited by 3 | Viewed by 3855
Abstract
This study demonstrates that flexible white LEDs, doped with diffusion particles and with a square column structure, have excellent luminosity, uniformity, and bending reliability. This large area (5 cm × 5 cm) square column flexible device had a smaller thickness (2 mm), and [...] Read more.
This study demonstrates that flexible white LEDs, doped with diffusion particles and with a square column structure, have excellent luminosity, uniformity, and bending reliability. This large area (5 cm × 5 cm) square column flexible device had a smaller thickness (2 mm), and enhancements in both luminous efficiency (29.5%) and uniformity (44.6%) compared to the characteristics of the 6 mm reference sample. Optimization of the reflective layer coating for the square column, flexible white LED was achieved with a higher luminous efficiency (171 lm/w) and uniformity (92%). We designed a novel lightning bolt electrode to improve reliability and bendability. After the bending test, the blue flexible LED had a lower bending diameter (10 mm) but more bending circles (increased to 2000 times. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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9 pages, 1800 KiB  
Article
Novel Method for Estimating Phosphor Conversion Efficiency of Light-Emitting Diodes
by Chih-Hao Lin, Che-Hsuan Huang, Yung-Min Pai, Chung-Fu Lee, Chien-Chung Lin, Chia-Wei Sun, Cheng-Huan Chen, Chin-Wei Sher and Hao-Chung Kuo
Crystals 2018, 8(12), 442; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst8120442 - 27 Nov 2018
Cited by 7 | Viewed by 3865
Abstract
This study presents a novel method for estimating the phosphor conversion efficiency of white light-emitting diodes (WLEDs) with different ratios of phosphors. Numerous attempts have been made for predicting the phosphor conversion efficiency of WLEDs using Monte Carlo ray tracing and the Mie [...] Read more.
This study presents a novel method for estimating the phosphor conversion efficiency of white light-emitting diodes (WLEDs) with different ratios of phosphors. Numerous attempts have been made for predicting the phosphor conversion efficiency of WLEDs using Monte Carlo ray tracing and the Mie scattering theory. However, because efficiency depends on the phosphor concentration, obtaining a tight match between this model and the experimental results remains a major challenge. An accurate prediction depends on various parameters, including particle size, morphology, and packaging process criteria. Therefore, we developed an efficient model that can successfully correlate the total absorption ratio to the phosphor concentration using a simple equation for estimating the spectra and lumen output. The novel and efficient method proposed here can accelerate WLED development by reducing costs and saving fabrication time. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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10 pages, 4913 KiB  
Article
Enhancing the Light-Extraction Efficiency of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes by Optimizing the Diameter and Tilt of the Aluminum Sidewall
by Yung-Min Pai, Chih-Hao Lin, Chun-Fu Lee, Chun-Peng Lin, Cheng-Huan Chen, Hao-Chung Kuo and Zhi-Ting Ye
Crystals 2018, 8(11), 420; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst8110420 - 08 Nov 2018
Cited by 18 | Viewed by 5085
Abstract
To realize high-efficiency AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency (LEE) is crucial. This paper proposes an aluminum-based sidewall reflector structure that could replace the conventional ceramic-based packaging method. We design optimization simulations and experimental results demonstrated the light power output [...] Read more.
To realize high-efficiency AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency (LEE) is crucial. This paper proposes an aluminum-based sidewall reflector structure that could replace the conventional ceramic-based packaging method. We design optimization simulations and experimental results demonstrated the light power output could be enhanced 18.38% of DUV-LEDs packaged with the aluminum-based sidewall. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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8 pages, 3934 KiB  
Article
Observation of Hybrid MAPbBr3 Perovskite Bulk Crystals Grown by Repeated Crystallizations
by Lung-Chien Chen, Kuan-Lin Lee and Shao-En Lin
Crystals 2018, 8(7), 260; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst8070260 - 25 Jun 2018
Cited by 11 | Viewed by 3663
Abstract
In this study, the inverse temperature crystallization method was used to produce bulk crystal CH3NH3PbBr3 (MAPbBr3) perovskite, and repeated crystallization processes were carried out to obtain a larger crystal size and develop a bulk material for [...] Read more.
In this study, the inverse temperature crystallization method was used to produce bulk crystal CH3NH3PbBr3 (MAPbBr3) perovskite, and repeated crystallization processes were carried out to obtain a larger crystal size and develop a bulk material for application in semiconductor devices. The material and optoelectronic properties of the MAPbBr3 perovskite crystals after the repeated processes were characterized. The X-ray diffraction (XRD) patterns of all samples demonstrated a pure perovskite phase. One strong diffraction peak located at 29.4°, which corresponds to the (200) perovskite plane, was observed after the first growth cycle. The mobilities for the samples after the first, second, and third growth cycles were calculated and resulted to be 0.9, 5.6, and 54.7 cm2/Vs, respectively, according to Mott–Gurney law. A higher mobility after the multiple crystallization processes indicated that the surface states caused by voids in the crystals favored electron transition in the perovskite material. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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Article
Manipulation of Si Doping Concentration for Modification of the Electric Field and Carrier Injection for AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes
by Mengqian Fang, Kangkai Tian, Chunshuang Chu, Yonghui Zhang, Zi-Hui Zhang and Wengang Bi
Crystals 2018, 8(6), 258; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst8060258 - 20 Jun 2018
Cited by 9 | Viewed by 3887
Abstract
Electron overflow is one of the key factors that limit the quantum efficiency for AlGaN-based deep-ultraviolet light-emitting diodes. In this work, we report a numerical study to improve the electron injection efficiency by manipulating the electric field profiles via doping the n-Al0.60 [...] Read more.
Electron overflow is one of the key factors that limit the quantum efficiency for AlGaN-based deep-ultraviolet light-emitting diodes. In this work, we report a numerical study to improve the electron injection efficiency by manipulating the electric field profiles via doping the n-Al0.60Ga0.40N electron source layer with different concentrations and reveal the physical mechanism of the Si doping effect on the electron and the hole injection. By utilizing the appropriate doping concentration, the electric field will reduce the electron drift velocity and, thus, the mean free path. Therefore, a higher electron capture efficiency by the multiple quantum wells (MQWs) and an increase of the hole concentration in the active region can be realized, resulting in an improved radiative recombination rate and an optical output power. Full article
(This article belongs to the Special Issue GaN-Based Optoelectronic Materials and Light Emitting Devices)
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