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Quantum Dots and Micro-LED Display 2.0

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A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Nanophotonics Materials and Devices".

Deadline for manuscript submissions: closed (20 August 2023) | Viewed by 42218

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Prof. Dr. Hao-Chung Kuo

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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
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Prof. Dr. Zhaojun Liu

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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
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Dear Colleagues,

Quantum Dots (QDs) have many unique physical and optical properties, such as high photoluminescence quantum yield, tunable emission over the entire visible spectral region, narrow emission spectrum, and high color purity. QDs have become a suitable candidate material in the display field, which has great potential to replace the traditional phosphor powder and increase the LCD color gamut range.

Micro-LED is an emerging flat panel display technology. As the name implies, micro-LED displays consist of arrays of microscopic LEDs forming the individual pixel elements. The applications include near-eye display, wearable devices, head mount devices, visible light communications, computer monitors, biomedical devices and projectors, which benefit from the obvious advantages of micro-LED display in brightness and saturation, as well as high display quality, even in high-intensity ambient light.

In this Special Issue, we would like to invite all papers related to the science and technology of Quantum Dots (QDs) ranging from materials research, device structure and properties, device applications for micro-LED display, manufacturing and high color gamut of display using QD. Research in the following fields is particularly welcomed:

QD or micro-LED display;
Energy applications;
Bio-applications;
Mechanical resonators;
Perovskite QD;
Cd-free QD;
Optoelectronics, such as lasing, lighting, micro-display, AR/VR, etc.

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

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Keywords

Perovskite quantum dots
Cd-free quantum dots
IR quantum dots
micro-LED display

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Published Papers (10 papers)

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Research

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10 pages, 3845 KiB

Open AccessArticle

Comparative Analysis of Optoelectrical Performance in Laser Lift-Off Process for GaN-Based Green Micro-LED Arrays

by Chuanbiao Liu, Feng Feng and Zhaojun Liu

Nanomaterials 2023, 13(15), 2213; https://doi.org/10.3390/nano13152213 - 30 Jul 2023

Cited by 5 | Viewed by 2308

Abstract

This work explores the pivotal role of laser lift-off (LLO) as a vital production process in facilitating the integration of Micro-LEDs into display modules. We specifically investigate the LLO process applied to high-performance gallium nitride (GaN)-based green Micro-LED arrays, featuring a pixel size of 20 × 38 μm on a patterned sapphire substrate (PSS). Scanning electron microscopy (SEM) observations demonstrate the preservation of the GaN film and sapphire substrate, with no discernible damage. We conduct a comprehensive analysis of the optoelectrical properties of the Micro-LEDs both before and after the LLO process, revealing significant enhancements in light output power (LOP) and external quantum efficiency (EQE). These improvements are attributed to more effective light extraction from the remaining patterns on the GaN backside surface. Furthermore, we examine the electroluminescence spectra of the Micro-LEDs under varying current conditions, revealing a slight change in peak wavelength and an approximate 10% decrease in the full width at half maximum (FWHM), indicating improved color purity. The current–voltage (I–V) curves obtained demonstrate the unchanged forward voltage at 2.17 V after the LLO process. Our findings emphasize the efficacy of LLO in optimizing the performance and color quality of Micro-LEDs, showcasing their potential for seamless integration into advanced display technologies. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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12 pages, 4004 KiB

Open AccessArticle

Ameliorating Uniformity and Color Conversion Efficiency in Quantum Dot-Based Micro-LED Displays through Blue–UV Hybrid Structures

by Tzu-Yi Lee, Wen-Chien Miao, Yu-Ying Hung, Yi-Hong Bai, Pei-Tien Chen, Wei-Ta Huang, Kuan-An Chen, Chien-Chung Lin, Fang-Chung Chen, Yu-Heng Hong and Hao-Chung Kuo

Nanomaterials 2023, 13(14), 2099; https://doi.org/10.3390/nano13142099 - 19 Jul 2023

Cited by 7 | Viewed by 3114

Abstract

Quantum dot (QD)-based RGB micro light-emitting diode (μ-LED) technology shows immense potential for achieving full-color displays. In this study, we propose a novel structural design that combines blue and quantum well (QW)-intermixing ultraviolet (UV)-hybrid μ-LEDs to achieve high color-conversion efficiency (CCE). For the first time, the impact of various combinations of QD and TiO₂ concentrations, as well as thickness variations on photoluminescence efficiency (PLQY), has been systematically examined through simulation. High-efficiency color-conversion layer (CCL) have been successfully fabricated as a result of these simulations, leading to significant savings in time and material costs. By incorporating scattering particles of TiO₂ in the CCL, we successfully scatter light and disperse QDs, effectively reducing self-aggregation and greatly improving illumination uniformity. Additionally, this design significantly enhances light absorption within the QD films. To enhance device reliability, we introduce a passivation protection layer using low-temperature atomic layer deposition (ALD) technology on the CCL surface. Moreover, we achieve impressive CCE values of 96.25% and 92.91% for the red and green CCLs, respectively, by integrating a modified distributed Bragg reflector (DBR) to suppress light leakage. Our hybrid structure design, in combination with an optical simulation system, not only facilitates rapid acquisition of optimal parameters for highly uniform and efficient color conversion in μ-LED displays but also expands the color gamut to achieve 128.2% in the National Television Standards Committee (NTSC) space and 95.8% in the Rec. 2020 standard. In essence, this research outlines a promising avenue towards the development of bespoke, high-performance μ-LED displays. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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11 pages, 2834 KiB

Open AccessArticle

Modified Distributed Bragg Reflectors for Color Stability in InGaN Red Micro-LEDs

by Wen-Chien Miao, Yu-Heng Hong, Fu-He Hsiao, Jun-Da Chen, Hsin Chiang, Chun-Liang Lin, Chien-Chung Lin, Shih-Chen Chen and Hao-Chung Kuo

Nanomaterials 2023, 13(4), 661; https://doi.org/10.3390/nano13040661 - 8 Feb 2023

Cited by 15 | Viewed by 4252

Abstract

The monolithic integration of InGaN-based micro-LEDs is being of interest toward developing full-color micro-displays. However, the color stability in InGaN red micro-LED is an issue that needs to be addressed. In this study, the modified distributed Bragg reflectors (DBRs) were designed to reduce the transmission of undesired spectra. The calculated optical properties of the InGaN red micro-LEDs with conventional and modified DBRs have been analyzed, respectively. The CIE 1931 color space and the encoded 8-bit RGB values are exhibited for the quantitative assessment of color stability. The results suggest the modified DBRs can effectively reduce the color shift, paving the way for developing full-color InGaN-based micro-LED displays. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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11 pages, 2068 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Reliability Perovskite Quantum Dots Using Atomic Layer Deposition Passivation for Novel Photonic Applications

by Tzu-Yi Lee, Tsau-Hua Hsieh, Wen-Chien Miao, Konthoujam James Singh, Yiming Li, Chang-Ching Tu, Fang-Chung Chen, Wen-Chung Lu and Hao-Chung Kuo

Nanomaterials 2022, 12(23), 4140; https://doi.org/10.3390/nano12234140 - 23 Nov 2022

Cited by 6 | Viewed by 2443

Abstract

In this study, we propose highly stable perovskite quantum dots (PQDs) coated with Al₂O₃ using atomic layer deposition (ALD) passivation technology. This passivation layer effectively protects the QDs from moisture infiltration and oxidation as well as from high temperatures and any changes in the material characteristics. They exhibit excellent wavelength stability and reliability in terms of current variation tests, long-term light aging tests, and temperature/humidity tests (60°/90%). A white-light system has been fabricated by integrating a micro-LED and red phosphor exhibiting a high data transmission rate of 1 Gbit/s. These results suggest that PeQDs treated with ALD passivation protection offer promising prospects in full-color micro-displays and high-speed visible-light communication (VLC) applications. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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17 pages, 16111 KiB

Open AccessArticle

Application of Mini-LEDs with Microlens Arrays and Quantum Dot Film as Extra-Thin, Large-Area, and High-Luminance Backlight

by Yen Lung Chen, Zhi Ting Ye, Wei Lai, Chang Che Chiu, Kuo Wei Lin and Pin Han

Nanomaterials 2022, 12(6), 1032; https://doi.org/10.3390/nano12061032 - 21 Mar 2022

Cited by 6 | Viewed by 3909

Abstract

The demand for extra-thin, large-area, and high-luminance flat-panel displays continues to grow, especially for portable displays such as gaming laptops and automotive displays. In this paper, we propose a design that includes a light guide layer with a microstructure above the mini-light-emitting diode light board. The light control microstructure of concave parabel-surface microlens arrays on a light-emitting surface increases the likelihood of total internal reflection occurring and improved the uniformity merit function. We used a 17 in prototype with quantum-dot and optical films to conduct our experiments, which revealed that the thickness of the module was only 1.98 mm. When the input power was 28.34 watts, the uniformity, average luminance, and CIE 1931 color space NTSC of the prototype reached 85%, 17,574 cd/m², and 105.37%, respectively. This module provided a flat light source that was extra thin and had high luminance and uniformity. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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13 pages, 1861 KiB

Open AccessArticle

Calculating the Effect of AlGaN Dielectric Layers in a Polarization Tunnel Junction on the Performance of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

by Yong Wang, Zihui Zhang, Long Guo, Yuxuan Chen, Yahui Li, Zhanbin Qi, Jianwei Ben, Xiaojuan Sun and Dabing Li

Nanomaterials 2021, 11(12), 3328; https://doi.org/10.3390/nano11123328 - 7 Dec 2021

Cited by 9 | Viewed by 2922

Abstract

In this work, AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with AlGaN as the dielectric layers in p⁺-Al_0.55Ga_0.45N/AlGaN/n⁺-Al_0.55Ga_0.45N polarization tunnel junctions (PTJs) were modeled to promote carrier tunneling, suppress current crowding, avoid optical absorption, and further enhance the performance of LEDs. AlGaN with different Al contents in PTJs were optimized by APSYS software to investigate the effect of a polarization-induced electric field (E_p) on hole tunneling in the PTJ. The results indicated that Al_0.7Ga_0.3N as a dielectric layer can realize a higher hole concentration and a higher radiative recombination rate in Multiple Quantum Wells (MQWs) than Al_0.4Ga_0.6N as the dielectric layer. In addition, Al_0.7Ga_0.3N as the dielectric layer has relatively high resistance, which can increase lateral current spreading and enhance the uniformity of the top emitting light of LEDs. However, the relatively high resistance of Al_0.7Ga_0.3N as the dielectric layer resulted in an increase in the forward voltage, so much higher biased voltage was required to enhance the hole tunneling efficiency of PTJ. Through the adoption of PTJs with Al_0.7Ga_0.3N as the dielectric layers, enhanced internal quantum efficiency (IQE) and optical output power will be possible. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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10 pages, 2078 KiB

Open AccessArticle

Investigation of Enhanced Ambient Contrast Ratio in Novel Micro/Mini-LED Displays

by Ke Zhang, Tingting Han, Wai-Keung Cho, Hoi-Sing Kwok and Zhaojun Liu

Nanomaterials 2021, 11(12), 3304; https://doi.org/10.3390/nano11123304 - 6 Dec 2021

Cited by 11 | Viewed by 4325

Abstract

In recent years, ambient contrast ratio (ACR) has become very critical for advanced outdoor displays, including transparent displays, portable displays, and so on. In this work, the ACR of typical flat panel displays was introduced, while LED-based displays showed distinctive advantages. Micro-LED displays with a different pitch of 10 μm, 15 μm, 30 μm, and 60 μm were fabricated and characterized. Various mini-LED and micro-LED panels were systematically investigated in the aspect of brightness, reflection phenomenon, and ACR to reveal their enormous potential for outdoor applications. Through a series of experiments and comparisons, three methods were proposed to further improve the ACR of LED-based panels, including optical method, antireflection coating, and structure optimization. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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10 pages, 2100 KiB

Open AccessArticle

High-Uniform and High-Efficient Color Conversion Nanoporous GaN-Based Micro-LED Display with Embedded Quantum Dots

by Yu-Ming Huang, Jo-Hsiang Chen, Yu-Hau Liou, Konthoujam James Singh, Wei-Cheng Tsai, Jung Han, Chun-Jung Lin, Tsung-Sheng Kao, Chien-Chung Lin, Shih-Chen Chen and Hao-Chung Kuo

Nanomaterials 2021, 11(10), 2696; https://doi.org/10.3390/nano11102696 - 13 Oct 2021

Cited by 30 | Viewed by 6788 | Correction

Abstract

Quantum dot (QD)-based RGB micro-LED technology is seen as one of the most promising approaches towards full color micro-LED displays. In this work, we present a novel nanoporous GaN (NP-GaN) structure that can scatter light and host QDs, as well as a new type of micro-LED array based on an NP-GaN embedded with QDs. Compared to typical QD films, this structure can significantly enhance the light absorption and stability of QDs. As a result, the green and red QDs exhibited light conversion efficiencies of 90.3% and 96.1% respectively, leading to improvements to the luminous uniformity of the green and red subpixels by 90.7% and 91.2% respectively. This study provides a viable pathway to develop high-uniform and high-efficient color conversion micro-LED displays. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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12 pages, 6842 KiB

Open AccessArticle

Mini-LEDs with Diffuse Reflection Cavity Arrays and Quantum Dot Film for Thin, Large-Area, High-Luminance Flat Light Source

by Zhi Ting Ye, Yuan Heng Cheng, Ku Huan Liu and Kai Shiang Yang

Nanomaterials 2021, 11(9), 2395; https://doi.org/10.3390/nano11092395 - 14 Sep 2021

Cited by 12 | Viewed by 3980

Abstract

Mini-light-emitting diodes (mini-LEDs) were combined with multiple three-dimensional (3D) diffuse reflection cavity arrays (DRCAs) to produce thin, large-area, high-brightness, flat light source modules. The curvature of the 3D free-form DRCA was optimized to control its light path; this increased the distance between light sources and reduced the number of light sources used. Experiments with a 12.3-inch prototype indicated that 216 mini-LEDs were required for a 6 mm optical mixing distance to achieve a thin, large-area surface with high brightness, uniformity, and color saturation of 23,044 cd/m², 90.13%, and 119.2, respectively. This module can serve as the local dimming backlight in next generation automotive displays. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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Review

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16 pages, 9899 KiB

Open AccessReview

Investigation of Autostereoscopic Displays Based on Various Display Technologies

by Fuhao Chen, Chengfeng Qiu and Zhaojun Liu

Nanomaterials 2022, 12(3), 429; https://doi.org/10.3390/nano12030429 - 27 Jan 2022

Cited by 15 | Viewed by 5610

Abstract

The autostereoscopic display is a promising way towards three-dimensional-display technology since it allows humans to perceive stereoscopic images with naked eyes. However, it faces great challenges from low resolution, narrow viewing angle, ghost images, eye strain, and fatigue. Nowadays, the prevalent liquid crystal display (LCD), the organic light-emitting diode (OLED), and the emerging micro light-emitting diode (Micro-LED) offer more powerful tools to tackle these challenges. First, we comprehensively review various implementations of autostereoscopic displays. Second, based on LCD, OLED, and Micro-LED, their pros and cons for the implementation of autostereoscopic displays are compared. Lastly, several novel implementations of autostereoscopic displays with Micro-LED are proposed: a Micro-LED light-stripe backlight with an LCD, a high-resolution Micro-LED display with a micro-lens array or a high-speed scanning barrier/deflector, and a transparent floating display. This work could be a guidance for Micro-LED applications on autostereoscopic displays. Full article

(This article belongs to the Special Issue Quantum Dots and Micro-LED Display 2.0)

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