• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.215-215
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• 2014

Red color light emitting diodes (LEDs) were fabricated using CdSe/CdZnS quantum dots (QDs). During the device fabrication process, oxygen plasma treatment on the ITO surface was performed to improve the interfacial contact between ITO anode and the hole injection layer. CdSe/CdZnS quantum dots were cross-linked to remove their surrounded organic surfactants. The device shows red emission at 622 nm, which is consistent with the dimension of the QDs (band gap=1.99 eV). The luminance shows 6026% improvement compared with that of LEDs fabricated without oxygen plasma treatment and quantum dots cross-linking process. This approach would be useful for the fabrication of high-performance QLEDs with ITO electrode and PEDOT:PSS hole injection layers.

• 한국전기전자재료학회논문지
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• 제36권6호
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• pp.537-546
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• 2023

Intrinsically stretchable light-emitting diodes, composed of stretchable electrodes, charge transport layers, and luminescent materials, have garnered significant interest for enhancing human well-being and advancing the field of deformable electronics. Various luminescent materials, such as perovskites and organics, have been integrated with stretchable elastomers to function as the stretchable emissive layers in these intrinsically stretchable LEDs. Stretchable conductors including Ag nanowire based percolating structures and conducting polymers have been utilized as stretchable transparent electrode. Despite this progress, their performances in terms of efficiency and stability remain challenging compared to their structurally stretchable and rigid LED counterparts. This review offers a comprehensive overview of recent advancements in intrinsically stretchable LEDs, focusing on material innovations.

• 한국세라믹학회지
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• 제54권6호
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• pp.449-469
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• 2017

The development of quantum dots (QDs) has had a significant impact on various applications, such as solar cells, field-effect transistors, and light-emitting diodes (LEDs). Through successful engineering of the core/shell heterostructure of QDs, their photoluminescence (PL) quantum yield (QY) and stability have been dramatically enhanced. Such high-quality QDs have been regarded as key fluorescent materials in realizing next-generation display devices. Particularly, electrically driven (or electroluminescent, EL) QD light-emitting diodes (QLED) have been highlighted as an alternative to organic light-emitting diodes (OLED), mostly owing to their unbeatably high color purity. Structural optimizations in QD material as well as QLED architecture have led to substantial improvements of device performance, especially during the past decade. In this review article, we discuss QDs with various semiconductor compositions and describe the mechanisms behind the operation of QDs and QLEDs and the primary strategies for improving their PL and EL performances.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.346.2-346.2
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• 2014

To use the GaN based light-emitting diodes (LEDs) as solid state lighting sources, the improvement of light extraction and internal quantum efficiency is essential factors for high brightness LEDs. In this study, we suggested the new materials system of a zinc tin oxide (ZTO) layer formed on blue LED epi-structures to improve the light extraction. ZTO is a representative n-type oxide material consisted of ZnO and SnO system. Moreover, ZTO is one of the promising oxide semiconductor material. Even though ZTO has higher chemical stability than IGZO owing to its SnO2 content this has high mobility and high reliability. After formation of ZTO layer on p-GaN layer by using the spin coating method, structural and optical properties are investigated. The x-ray diffraction (XRD) measurement results show the successful formation of ZTO. The photoluminescence (PL) and absorption spectrum shows that it has 3.6-4.1eV band gap. Finally, the light extraction properties of ZTO/LED chip using electroluminescence (EL) measurement were investigated. The experimental and theoretical analyses were simultaneously conducted.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권4호
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• pp.454-461
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• 2015

Light enhancement of GaN based light emitting diodes (LEDs) have been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental results were further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), Surface nano-porous (porous LED) and Surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency.

• Current Optics and Photonics
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• 제3권2호
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• pp.164-171
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• 2019

Photoluminescence (PL) properties of GaN-based light-emitting diodes (LEDs) were analyzed to study the effects of carrier leakage on the luminescence properties at room temperature. The electrical leakage and PL properties were compared for LEDs showing leakages at forward bias and an LED with an intentional leakage path formed by connecting a parallel resistance of various values. The leakages at the forward bias, which could be observed from the current-voltage characteristics, resulted in an increase in the excitation laser power density for the maximum PL efficiency (ratio of PL intensity to excitation power) as well as a reduction in the PL intensity. The effect of carrier leakages on PL properties was similar to the change in PL properties owing to a reduction of the photovoltage by a reverse current since the direction of the carrier movement under photoexcitation is identical to that of the reverse current. Valid relations between PL properties and electrical properties were observed as the PL properties deteriorated with an increase in the carrier leakage. The results imply that the PL properties of LED chips can be an indicator of the electrical properties of LEDs.

• 센서학회지
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• 제31권4호
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• pp.238-243
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• 2022

In this study, a pyrene-core single molecule with amino (-NH₂) functional group material was hybridized using ZnO quantum dots (QDs). The suppressed performance of the 1-aminopyrene (1-PyNH₂) single molecule as an emissive layer (EML) in light-emitting diodes (LEDs) was exploited by adopting the ZnO@1-PyNH₂ core-shell structure. Unlike pristine 1-PyNH₂ molecules, the ZnO@1-PyNH₂ hybrid QDs formed energy proximity levels that enabled charge transfer. This result can be interpreted as an improvement in surface roughness. The uniform and homogeneous EML alleviates dark-spot degradation. Moreover, LEDs with the ITO/PEDOT:PSS/TFB/EML/TPBi/LiF/Al configuration were fabricated to evaluate the performance of two emissive materials, where pristine-1-PyNH₂ molecules and ZnO@1-PyNH₂ QDs were used as the EML materials to verify the improvement in electrical characteristics. The ZnO@1-PyNH₂ LEDs exhibited blue luminescence at 443 nm (FWHM = 49 nm), with a turn-on voltage of 4 V, maximum luminance of 1500 cd/m², maximum luminous efficiency of 0.66 cd/A, and power efficiency of 0.41 lm/W.

• Journal of Ceramic Processing Research
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• 제13권spc1호
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• pp.75-77
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• 2012

The AlGaN-based vertical light-emitting diodes (LEDs) on thick GaN epilayer were fabricated by a hydride vapor phase epitaxy with multi sliding boat system. The optical and electrical characteristics of AlGaN-based vertical LEDs were evaluated using a scanning electron microscopy, electroluminescence and I-V measurements. The AlGaN-based vertical LEDs structure has hexagonal symmetry, 500 ㎛ in diameter and above 67 ㎛ in growth thickness. At the room-temperature, the broaded strong peak and relatively high intensity peak were gradually measured at 405 nm with increasing injection current. And a forward operator voltage was measured to be about 7.5 V.

• 대한환경공학회지
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• 제33권8호
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• pp.591-597
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• 2011

본 연구는 담수미세조류의 일종인 클로렐라를 발광다이오드를 이용하여 효율적으로 배양하기 위한 조건을 찾기 위해 수행되었다. 클로렐라 배양에 최적인 파장을 찾기 위해 청색, 적색, 백색, 그리고 혼합광을 클로렐라가 포함된 반응기에 각각 조사하여 성장속도 및 셀농도를 측정하였다. 적색파장이 클로렐라의 성장에 가장 효율적이었으며, 광량이 증가할수록 성장속도 및 셀농도도 광량에 비례하여 가장 많이 증가하였다. 클로렐라의 초기 농도에 따른 성장속도는 초기 농도가 증가함에 따라 그림자 효과에 의해 감소하였다. 공기 공급에 따른 성장특성을 살펴보기 위해 반응기에 미세공기를 연속적으로 주입하였는데, 반응속도 및 셀농도는 공기를 주입하지 않은 경우에 비해 2배와 10배 증가함을 알 수 있었다. 본 연구를 통해 클로렐라를 효과적으로 배양하기 위해서는 적색파장의 발광다이오드를 광원으로 사용하고 반응기에 공기를 연속적으로 주입하는 것이 효과적임을 알 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.92-92
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• 2010

Replacing the existing illumination with solid-state lighting devices, such as light-emitting diodes (LEDs) are expected to reduce energy consumption and environmental pollution as they provide better efficiency and longer lifetimes. Currently, white light emitting diodes are composed of UV or blue LED with down-converting materials such as highly luminescent phosphors White light-emitting diodes (LED) were fabricated with multi-shell nanocrystal quantum dots for enhanced luminance and improved stability over time. Multi-shell quantum dots (QDs) were synthesized through one pot process by using the Successive Ionic Layer Adsorption and Reaction (SILAR) method. As prepared, the multi-shell QD has cubic lattice of zinc-blend structure with semi-spherical shape with quantum yield of higher than 60 % in solution. Further, highly fluorescent multi-shell QD was deposited on the blue LED, which resulted in QD-based white LED with high luminance with excellent color rendering properties.