Three‐Dimensional Branched Nanowire Heterostructures as Efficient Light‐Extraction Layer in Light‐Emitting Diodes

Ye, Byeong Uk; Kim, Buem Joon; Park, Joonmo; Jeong, Hu Young; Park, Jae Yong; Kim, Jong Kyu; Hur, Jin Hoe; Kim, Myung Hwa; Lee, Jong Lam; Baik, Jeong Min

doi:10.1002/adfm.201303914

Cited by 14 publications

(14 citation statements)

References 38 publications

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“…This is due to the fact that most of the generated photons from the active layer are captured by LEDs because of total internal reection (TIR) at the interface of semiconductor with air. 6,7 To solve this problem, a number of solutions based on geometrical optics have been proposed including integration of two-dimensional (2D) photonic crystal (PC) patterns, [8][9][10][11][12] growth of nano-wires such as zinc oxide (ZnO), [13][14][15][16][17][18][19] and nano-patterns using electron beam lithography. 20,21 However, these methods are intrinsically expensive, exhibit low-throughput and are limited to small-area processing.…”

Section: Introductionmentioning

confidence: 99%

Nano-imprinting of refractive-index-matched indium tin oxide sol–gel in light-emitting diodes for eliminating total internal reflection

et al. 2018

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Section: Introductionmentioning

confidence: 99%

Nano-imprinting of refractive-index-matched indium tin oxide sol–gel in light-emitting diodes for eliminating total internal reflection

et al. 2018

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“…Various morphologies of ZnO nanostructures such as, nanorods (NR), nanowires, and hierarchical 3D nanostructures, typically grown by a hydrothermal technique, were suggested for enhancing the LEE of GaN LEDs . Although the effective refractive index ( n air = 1 < n < n ZnO_bulk = 2.0) of the ZnO‐NR layer, determined by its porosity, is appropriate in mitigating the abrupt change in the refractive indices between GaN and air, the Fresnel reflection or TIR still occurs at the interfaces between GaN and the ZnO‐NR layer or air, thereby limiting the enhancement . On the other hand, Ye et al fabricated 3D branched ZnO/MgO nanowire heterostructures, in which ZnO nanowires were grown by the hydrothermal method and MgO branches by electron‐beam evaporation.…”

Section: Introductionmentioning

confidence: 99%

“…Although the effective refractive index ( n air = 1 < n < n ZnO_bulk = 2.0) of the ZnO‐NR layer, determined by its porosity, is appropriate in mitigating the abrupt change in the refractive indices between GaN and air, the Fresnel reflection or TIR still occurs at the interfaces between GaN and the ZnO‐NR layer or air, thereby limiting the enhancement . On the other hand, Ye et al fabricated 3D branched ZnO/MgO nanowire heterostructures, in which ZnO nanowires were grown by the hydrothermal method and MgO branches by electron‐beam evaporation. They observed enhancement of 21% in the LOP, which is attributed not only to the ZnO backbone nanorods but also the MgO branches; the additional effect of light extraction is provided by the branches by breaking the wave‐guiding mode.…”

Section: Introductionmentioning

confidence: 99%

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

Park

Kim

Kang

et al. 2016

Advanced Optical Materials

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the GaN epitaxial layer quality, [8] the light trapping due to the total internal reflection (TIR) still limits the light extraction efficiency (LEE) of GaN. This is caused by the abrupt change in the refractive indices across the interface between GaN (n = 2.5) and the sapphire substrate (n = 1.8) or air (n = 1).Many approaches have been suggested for mitigating the TIR effect such as, surface texturing, [9][10][11][12][13] antireflection (AR) coatings, [14][15][16] and photonic crystal structures. [17,18] The top-down surface texturing techniques using dry or photoelectrochemical etching have demonstrated nearly twofold enhancement in the light output power (LOP). [19] However, these etching techniques have innate limitations for use in lateral LEDs because the top p-GaN layer is so thin (typically less than 200 nm) that the etching process for p-GaN must be exactly controlled to avoid degradation of the GaN LEDs. Therefore, bottom-up approaches such as AR coatings with graded refractive index [20] or photonic crystal structures [21] are typically utilized in the lateral LEDs.ZnO nanostructures are one of the most intensively investigated materials that are integrated on the surface of the LEDs for reducing the TIR without compromising the electrical properties. Various morphologies of ZnO nanostructures such as, nanorods (NR), nanowires, and hierarchical 3D nanostructures, typically grown by a hydrothermal technique, were suggested for enhancing the LEE of GaN LEDs. [22][23][24][25] Although the effective refractive index (n air = 1 < n < n ZnO_bulk = 2.0) of Recently, 3D nanostructures have attracted much interest because of their interesting electrical/optical properties such as wave guiding modes, light scattering, antireflection effects, etc. In this work, a facile yet efficient method for the fabrication of hierarchical 3D indium tin oxide (ITO) nanotrees (NTs) and their integration in GaN-based blue-light-emitting diodes (LEDs) for efficient light-extraction are reported. The ITO NTs are fabricated by the obliqueangle (≈85°) deposition method at 240 °C using electron-beam evaporation. The ITO NTs grow via a self-catalytic vapor-liquid-solid mechanism with the branches having an epitaxial relationship with the trunks. The ITO NTs successively deposited on an ITO thin film as a p-contact layer are annealed at 600 °C for 1 min under ambient air in order to form a transparent ohmic contact. The indium gallium nitrde/gallium nitride (InGaN/GaN) LED with ITO NTs presents a 29.5% enhancement in the light output power at an injection current of 20 mA, compared to the reference LED with an ITO thin film p-contact. This enhancement is ascribed to the effective light extraction of the ITO NTs due to to the gradually decreasing profile of the refractive index from 2.08 (ITO thin film), 1.15 (dense ITO NTs), 1.06 (porous ITO NTs) to 1.0 (air). These results are in good agreement with the optical simulation by the COMSOL wave optics module.Figure 7. Light beam profile images of a) the reference and b) ITO-NT-integrate...

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“…Zhou and SnO 2 individual components in lithium-ion battery application [25]. However, the methods reported for preparing these branched structures typically involve multi-steps and are inefficient [28][29][30][31][32][33]. For example, a general approach for branched materials synthesis is to use branched nanoporous templates such as anodic aluminum oxide (AAO) templates, but the synthesis of the branched AAO templates consists of consecutive anodization steps [32].…”

Section: Introductionmentioning

confidence: 99%

“…For example, a general approach for branched materials synthesis is to use branched nanoporous templates such as anodic aluminum oxide (AAO) templates, but the synthesis of the branched AAO templates consists of consecutive anodization steps [32]. Another general approach for the synthesis of branched materials is to assemble secondary branches on as-prepared nanowire backbones with the assistance of seeds, catalysts and high reaction temperature [24,25,29,33].…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional branched single-crystal β-Co(OH)2 nanowire array and its application for supercapacitor with excellent electrochemical property

Wang

Zhang

et al. 2014

Nano Energy

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We have for the first time fabricated a unique three-dimensional branched single-crystal β-Co(OH) 2 nanowire array supported on Ni foam. This structure is formed by the splitting crystal growth effect combined with the specific topological structure of β-Co(OH) 2. A branched Co 3 O 4 @MnO 2 core-shell nanowire array is prepared for use as supercapactor electrode. At a current density of 10 mA cm-2 , the branched Co 3 O 4 @MnO 2 core-shell nanowire array exhibits 0.99 F cm-2 of areal capacitance, which is 69.3% of the capacitance (1.43 F cm-2) measured at 1 mA cm-2. In addition, the branched core-shell hybrid can still retain 93.6% of the initial capacitance after 5000 cycles. Such excellent electrochmical performance of the branched Co 3 O 4 @MnO 2 core-shell nanowire array is attributed to the unique configuration and the strong synergistic effect from the porous Co 3 O 4 nanowire core and the ultrathin MnO 2 shell.

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Three‐Dimensional Branched Nanowire Heterostructures as Efficient Light‐Extraction Layer in Light‐Emitting Diodes

Cited by 14 publications

References 38 publications

Nano-imprinting of refractive-index-matched indium tin oxide sol–gel in light-emitting diodes for eliminating total internal reflection

Nano-imprinting of refractive-index-matched indium tin oxide sol–gel in light-emitting diodes for eliminating total internal reflection

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

Three-dimensional branched single-crystal β-Co(OH)2 nanowire array and its application for supercapacitor with excellent electrochemical property

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