Improving light-emitting diode performance through sapphire substrate double-side patterning

Kang, Ho Ju; Cho, Sang Uk; Kim, Eung Soo; Kim, Chang-Seok; Jeong, Myung Yung

doi:10.1117/1.oe.52.2.023002

Cited by 11 publications

(7 citation statements)

References 11 publications

(14 reference statements)

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“…We highlight that the impact of designed outcoupling structures becomes more significant in absorptive LED devices (e.g., InGaN/GaN LEDs with a high fraction of the In composition) . Previous reports have shown that for PSS LED devices cone patterns provide more efficient light extraction and improved GaN crystallinity as compared to hemisphere patterns. − Therefore, we postulate that even larger wall-plug efficiency could be obtained in CES LEDs that incorporate cone patterns. Additionally, the inner air cavities in the CES pattern help release the stress accumulated during the heteroepitaxial growth of GaN layers on the sapphire substrate, which leads to reduced wafer bow (Supporting Information Figure S7) .…”

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confidence: 75%

Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes

Moon

Jang

et al. 2016

Nano Lett.

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Two-dimensional high-index-contrast dielectric gratings exhibit unconventional transmission and reflection due to their morphologies. For light-emitting devices, these characteristics help guided modes defeat total internal reflections, thereby enhancing the outcoupling efficiency into an ambient medium. However, the outcoupling ability is typically impeded by the limited index contrast given by pattern media. Here, we report strong-diffraction, high-index-contrast cavity engineered substrates (CESs) in which hexagonally arranged hemispherical air cavities are covered with a 80 nm thick crystallized alumina shell. Wavelength-resolved diffraction measurements and Fourier analysis on GaN-grown CESs reveal that the high-index-contrast air/alumina core/shell patterns lead to dramatic excitation of the low-order diffraction modes. Large-area (1075 × 750 μm(2)) blue-emitting InGaN/GaN light-emitting diodes (LEDs) fabricated on a 3 μm pitch CES exhibit ∼39% enhancement in the optical power compared to state-of-the-art, patterned-sapphire-substrate LEDs, while preserving all of the electrical metrics that are relevant to LED devices. Full-vectorial simulations quantitatively demonstrate the enhanced optical power of CES LEDs and show a progressive increase in the extraction efficiency as the air cavity volume is expanded. This trend in light extraction is observed for both lateral- and flip-chip-geometry LEDs. Measurements of far-field profiles indicate a substantial beaming effect for CES LEDs, despite their few-micron-pitch pattern. Near-to-far-field transformation simulations and polarization analysis demonstrate that the improved extraction efficiency of CES LEDs is ascribed to the increase in emissions via the top escape route and to the extraction of transverse-magnetic polarized light.

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confidence: 75%

Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes

Moon

Jang

et al. 2016

Nano Lett.

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“…Parabolic nanostructures were manufactured on the PMMA surface by depositing silicon dioxide (SiO 2 ) via a thermal oxidation process. In a subsequent process, the nanostructured surface was further modified via high-density plasma chemical vapor deposition using SiO 2 (Novellus Co., Canada), and thermal nanoimprint lithography was conducted on the PMMA film (Obducat, Sweden) . All stamps were coated with an antisticking layer (Optool DSX, Daikin Chemicals) for the subsequent demolding process …”

Section: Methodsmentioning

confidence: 99%

“…In a subsequent process, the nanostructured surface was further modified via high-density plasma chemical vapor deposition using SiO 2 (Novellus Co., Canada), and thermal nanoimprint lithography was conducted on the PMMA film (Obducat, Sweden). 14 All stamps were coated with an antisticking layer (Optool DSX, Daikin Chemicals) for the subsequent demolding process. 15 Characterization of the Imprinted Surface.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Nanostructured Multifunctional Surface with Antireflective and Antimicrobial Characteristics

Kim

Jung²,

Kim³

et al. 2015

ACS Appl. Mater. Interfaces

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129

108

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Functional polymeric films with antireflective and hydrophobic properties have been widely used for electronic device displays. However, the design of such functional films with an antimicrobial characteristic has been a challenge. We designed a nanostructured surface using a rigorous coupled-wave analysis to obtain a period of 300 nm and an aspect ratio of 3.0 on a flat poly(methyl methacrylate) film. The fabricated nanostructure was hydrophobic and exhibited the desired optical characteristics with a reflectance of less than 0.5% over the visible wavelength range. Furthermore, the nanoimprinted polymer film exhibited antimicrobial characteristics and low adhesion when compared with the corresponding flat surface. The results suggest that the nanostructured surface designed in this study is multifunctional and should be suitable for the production of protective optical and hygienic polymer films for the displays of portable electronic devices.

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“…7(a) and (b). This is because the concave cones are beneficial for the escape of light with middle emission angles, which results from the inclined surface that reduces the incident angles for this light [22], [46], [47]. However, the rougher surface can more significantly decrease the transmittance of light with small incident angles because of the stronger backward scattering, as shown in Fig.…”

Section: Light-extraction Mechanisms Of Msparmmentioning

confidence: 99%

Investigation of Light-Extraction Mechanisms of Multiscale Patterned Arrays With Rough Morphology for GaN-Based Thin-Film LEDs

Cao

et al. 2019

IEEE Access

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Micro-scale patterned arrays and nano-scale rough morphology are promising for improving the light-extraction performance of GaN-based thin film light-emitting diodes (TFLEDs), while the lightextraction mechanisms of the multiscale architectures combining these two structures have not been investigated yet. In this report, we have adopted a pattern transfer and wet etching combined method to fabricate multiscale patterned arrays with rough morphology (msPARM) on n-GaN layers for TFLEDs and investigated their light-extraction mechanisms by the finite-difference time domain and ray-tracing combined method. The results show that the TFLEDs achieve the maximum radiant efficacy using the msPARM with an etching time of 8 min, which is increased by 16.3% and 1.7% compared with that achieved using only the patterned arrays or only the rough morphology, respectively. Most importantly, optical simulation reveals that the msPARM can provide a high transmittance for light with large emission angles from the active region using the inclined surface of micro-scale concave cones, while effectively suppressing the reflection loss for light with small emission angles using the scattering effect of nano-scale rough morphology, resulting in enhancing the light-extraction of the TFLEDs. Consequently, this study can provide a better understanding to design the multiscale structures for achieving high efficiency LEDs.INDEX TERMS GaN-based thin-film light-emitting diodes, light extraction, finite-difference time domain, ray-tracing, multiscale structure. I. INTRODUCTIONLight-emitting diodes (LEDs) led to a revolution in lighting and have gradually replaced conventional solid-state lighting sources because of their high brightness and long lifetime [1]. GaN-based thin-film LEDs (TFLEDs) hold promise as a high-power and high-quality lighting source because of their high light extraction, good heat dissipation, and flexible chip size [1]-[3]. The radiant efficacy is one of the most essential performance indicators for TFLEDs applications [4], defined as the ratio of radiant power to the injected electrical power. This performance is contributed by the internal quantum efficiency (IQE) and light-extraction efficiency (LEE).The associate editor coordinating the review of this manuscript and approving it for publication was Jiang Wu.

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Improving light-emitting diode performance through sapphire substrate double-side patterning

Cited by 11 publications

References 11 publications

Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes

Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes

Nanostructured Multifunctional Surface with Antireflective and Antimicrobial Characteristics

Investigation of Light-Extraction Mechanisms of Multiscale Patterned Arrays With Rough Morphology for GaN-Based Thin-Film LEDs

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