Characteristics and simulation analysis of GaN‐based vertical light emitting diodes via wafer‐level additional surface roughening process

Bae, Seong-Ju; Choi, Jeongmin; Kim, Dong-Hyun; Ju, Inchan; Shin, Chan-Soo; Ko, Chul-Gi; Yu, Jae Su

doi:10.1002/pssa.201127557

Cited by 3 publications

(3 citation statements)

References 17 publications

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“…Therefore, decreasing Fresnel reflection and expanding the critical angle at the GaN-air interface will be necessary. Several approaches have been developed to expand the critical angle at the GaN-air interface; for example, surface roughening through wet chemical etching, 3,4 dry etching, [5][6][7] or the fabrication of heterogeneous random structures comprising zinc oxide (ZnO) [8][9][10][11] or indium tin oxide (ITO) 12,13 on the surface of the LED to prevent total internal reflection. The application of periodic photonic crystal (PhC) structures is also a common method for expanding the critical angle at the GaN-air interface.…”

Section: Introductionmentioning

confidence: 99%

Using nanoimprint lithography to improve the light extraction efficiency and color rendering of dichromatic white light-emitting diodes

Lee

Chen

et al. 2015

Nanoscale

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Despite the efficiency of gallium nitride (GaN)-based blue light-emitting diodes (LEDs), the light extraction arising from the packaging of the phosphor remains an important issue when enhancing the performance of dichromatic white LEDs. In this study, we employed a simple, inexpensive nanoimprinting process to increase both the light extraction efficiency and color rendering of dichromatic white LEDs. We employed the rigorous coupled wave approach (RCWA) to optimize the light extraction efficiency of yellow and blue light. We found that the presence of the light extracting structures could also improve the color rendering of the dichromatic white LEDs, due to the different light extraction efficiencies of the textured structures at different wavelengths. After fabricating inverted pyramid structures on the surface of the encapsulation layer, the intensity of the blue light at 455 nm increased by 20%. When we further considered the color rendering and correlated color temperature (CCT), the enhancement of blue light was 15% and that of yellow light was 4%. Meanwhile, the light extraction of the intensity dip near 490 nm was enhanced significantly (by 25%), resulting in an increased dip-intensity of light at 490 nm relative to the intensities of the blue and yellow light. Accordingly, the color rendering index (CRI) of this dichromatic white LED increased from 69 to 73. Because it improved both the light extraction efficiency and color rendering of dichromatic white LEDs, this simple method should be very helpful for enhancing their applications in solid state illumination.

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Section: Introductionmentioning

confidence: 99%

Using nanoimprint lithography to improve the light extraction efficiency and color rendering of dichromatic white light-emitting diodes

Lee

Chen

et al. 2015

Nanoscale

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“…On the other hand, a major source of optical output power loss is due to light being trapped within the materials due to the optical properties,which affects the light extraction efficiency of the LED. Various methods, such as surface roughening [8], [9], [10], [11], patterned substrates [12], [13], [14], integration of DBRs and photonic crystals [15], [16], [17] are being utilized by research groups to improve LED extraction efficiency [18]. These methods add additional complexities to the fabrication process of the LEDs.…”

mentioning

confidence: 99%

Improvement in the Light Extraction of Blue InGaN/GaN-Based LEDs Using Patterned Metal Contacts

Kadiyala

Lee

Rodak

et al. 2014

IEEE J. Electron Devices Soc.

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We demonstrate a method to improve the light extraction from an LED using photonic crystal (PhC)-like structures in metal contacts. A patterned metal contact with an array of Silicon Oxide (SiO x ) pillars (440 nm in size) on an InGaN/GaNbased MQW LED has shown to increase output illumination uniformity through experimental characterization. Structural methods of improving light extraction using transparent contacts or dielectric photonic crystals typically require a tradeoff between improving light extraction and optimalelectrical characteristics.The method presented here provides an alternate solution to provide a 15% directional improvement (surface normal) in the radiation profile and ∼ 30% increase in the respective intensity profile without affecting the electrical characteristics of the device. Electron beam patterning of hydrogen silesquioxane (HSQ), a novel electron beam resist is used in patterning these metal contacts. After patterning, thermal curing of the patterned resist is done to form SiO x pillars. These SiO x pillars aid as a mask for transferring the pattern to the p-metal contact. Electrical and optical characterization results of LEDs fabricated with and without patterned contacts are presented. We present the radiation and intensity profiles of the planar and patterned devices extracted using Matlab-based image analysis technique from 200 μm (diameter) circular unpackaged LEDs.Index Terms-Electron beam lithography (EBL), light emitting diode (LED), patterning, photonic crystal (PC), hydrogen silesquioxane (HSQ).

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“…In the recent years, several extraction methods have been developed and improved to address this problem. Techniques like chip shaping [8], [9], encapsulation [10], surface roughening [11], [12], [13], [14], patterned substrates [15], [16], [17], [18], integration of DBRs and photonic crystals [19], [20], [21] and the combination of them are usually deployed to improve the extraction in the LEDs. Each of these techniques has a unique approach and addresses a particular segment of the issue.…”

Section: Statement Of Dissertationmentioning

confidence: 99%

Design, Fabrication and Characterization of Photonic Crystal Light-Emitting Diodes for Solid-State Lighting

Kadiyala¹

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Residential, commercial, and industrial lighting applications contribute to ~19% of total energy consumption worldwide. The application of more efficient sources of lighting, such as solid-state lighting (SSL) sources, could result in potential energy savings of about 65%. Current technologies employ semiconductor-based light-emitting diodes (LEDs) as the core elements of SSL devices to provide generalpurpose light in a wide range of color temperatures. However, there still exists several device level issues, such as poor material quality, low quantum efficiencies, large percentage of light being trapped, etc. These non-idealities are barriers for SSL sources replacing incandescent and compact fluorescent sources on an equivalent lumens-per-watt basis. WVU SSL research interests involve addressing device-level issues associated with III-V nitride materials, as well as optimizing the growth of materials and performance of fabricated devices. One major goal of research efforts is to provide solutions for improvement in light extraction in III-nitride-based devices Dawson for his guidance towards my thesis work. Dr. Dawson's wisdom, patience and constant encouragement are some of the reasons that have made the findings in this thesis possible.

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Characteristics and simulation analysis of GaN‐based vertical light emitting diodes via wafer‐level additional surface roughening process

Cited by 3 publications

References 17 publications

Using nanoimprint lithography to improve the light extraction efficiency and color rendering of dichromatic white light-emitting diodes

Using nanoimprint lithography to improve the light extraction efficiency and color rendering of dichromatic white light-emitting diodes

Improvement in the Light Extraction of Blue InGaN/GaN-Based LEDs Using Patterned Metal Contacts

Design, Fabrication and Characterization of Photonic Crystal Light-Emitting Diodes for Solid-State Lighting

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