• 한국전기전자재료학회논문지
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• 제24권1호
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• pp.7-11
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• 2011

Sapphire substrate was patterned by a selective chemical wet etching technique, and GaN/InGaN structures were grown on this substrate by MOVPE (Metal Organic Vapor Phase Epitaxy). The surface of grown GaN on patterned sapphire substrate (PSS) has good morphology and uniformity. The patterned sapphire substrate LED showed better light output than conventional LED that improvement 50%. We think these results come from enhancement of internal quantum efficiency by decrease of threading dislocation and increase of light extraction efficiency. Also these LED showed more uniform emission distribution in angle than conventional LED.

• 대한전자공학회논문지SD
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• 제44권4호
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• pp.91-96
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• 2007

사파이어 기반의 GaN LED의 광추출 효율을 시뮬레이션을 이용하여 정량적으로 평가하였다. 각각의 LED는 ray-tracing 시뮬레이션을 이용하여 광추출 효율을 계산하였다. 본 연구에는 PSS(patterned sapphire substrate) LED와 flat LED의 비교 분석을 통하여, LED에서의 사파이어 기판의 패턴이 광추출에 미치는 영향을 설명하였다. 또한, 각각의 칩에서 반사막의 반사도가 광추출에 미치는 영향을 분석하고, 그 원인을 시뮬레이션을 이용하여 설명하였다. 한편, 사파이어 패턴에 의한 광추출효율의 변화 효과를 공기(air)와 실리콘(silicone) 분위기에서 시뮬레이션을 수행하였다. 이러한 시뮬레이션 기술을 통해 광추출 효율의 개선 정도를 정량적으로 평가할 수 있었으며, 이러한 연구가 향후 고효율 LED 개발에 도움을 줄 것으로 판단된다.

• Current Optics and Photonics
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• 제1권4호
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• pp.358-363
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• 2017

In this study, we present a detailed investigation of luminescence properties of a blue light-emitting diode using InGaN/GaN (indium component is 17.43%) multiple quantum wells as the active region grown on patterned sapphire substrate by low-pressure metal-organic chemical vapor deposition (MOCVD). High-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman scattering (RS) and photoluminescence (PL) measurements are employed to study the crystal quality, the threading dislocation density, surface morphology, residual strain existing in the active region and optical properties. We conclude that the crystalline quality and surface morphology can be greatly improved, the red-shift of peak wavelength is eliminated and the superior blue light LED can be obtained because the residual strain that existed in the active region can be relaxed when the LED is grown on patterned sapphire substrate (PSS). We discuss the mechanisms of growing on PSS to enhance the superior luminescence properties of blue light LED from the viewpoint of residual strain in the active region.

• 한국재료학회지
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• 제15권10호
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• pp.626-631
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• 2005

GaN-related compound semiconductors were grown on the corrugated interface substrate using a metalorganic chemical vapor deposition system to increase the optical power of white LEDs. The patterning of substrate for enhancing the extraction efficiency was processed using an inductively coupled plasma reactive ion etching system and the surface morphology of the etched sapphire wafer and that of the non-etched surface were investigated using an atomic force microscope. The structural and optical properties of GaN grown on the corrugated interface substrate were characterized by a high-resolution x-ray diffraction, transmission electron microscopy, atomic force microscope and photoluminescence. The roughness of the etched sapphire wafer was higher than that of the non-etched one. The surface of III-nitride films grown on the hemispherically patterned wafer showed the nano-sized pin-holes that were not grown partially. In this case, the leakage current of the LED chip at the reverse bias was abruptly increased. The reason is that the hemispherically patterned region doesn't have (0001) plane that is favor for GaN growth. The lateral growth of the GaN layer grown on (0001) plane located in between the patterns was enhanced by raising the growth temperature ana lowering the reactor pressure resulting in the smooth surface over the patterned region. The crystal quality of GaN on the patterned substrate was also similar with that of GaN on the conventional substrate and no defect was detected in the interface. The optical power of the LED on the patterned substrate was $14\%$ higher than that on the conventional substrate due to the increased extraction efficiency.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권3호
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• pp.199-205
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• 2006

Patterned sapphire substrates (PSS) were fabricated by a simple wet etching process with $SiO_2$ stripe masks and a mixed solution of $H_2SO_4$ and $H_3PO_4$. GaN layers were epitaxially grown on the PSS under the optimized 2-step growth condition of metalorganic vapor deposition. During the 1st growth step, GaN layers with triangular cross sections were grown on the selected area of the surface of the PSS, and in the 2nd growth step, the GaN layers were laterally grown and coalesced with neighboring GaN layers. The density of threading dislocations on the surface of the coalesced GaN layer was $2{\sim}4\;{\times}\;10^7\;cm^{-2}$ over the entire region. The epitaxial structure of near-UV light emitting diode (LED) was grown over the GaN layers on the PSS. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the PSS were remarkably increased when compared to the conventional LED structure grown on the flat sapphire substrate. The reduction in TD density and the decrease in the number of times of total internal reflections of the light flux are mainly attributed due to high level of scattering on the PSS.

• 마이크로전자및패키징학회지
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• 제18권4호
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• pp.91-95
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• 2011

GaN 기반의 LED에서 광 추출 효율을 정량적으로 분석하였다. Ray-Tracing기반의 시뮬레이션을 이용하여 사파이어 기판에 형성된 패턴의 형태, 크기, 깊이, 간격들을 분석하여 최적의 패턴 요소들을 도출하였다. 시뮬레이션의 결과로 최적의 패턴 형태는 반구 형태에서 높은 광 추출 효율을 보였다. 일반적인 패턴이 없는 사파이어 기판을 사용한 LED의 광 추출 효율보다 반구 형태의 패턴을 가진 사파이어 기판에서 약 40% 향상된 광 추출 효율을 보였다.

• 한국전기전자재료학회논문지
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• 제28권10호
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• pp.676-681
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• 2015

Recently many studies being carried out to increase the light efficiency of LED. The external quantum efficiency of LED, generally the light efficiency, is determined by the internal quantum efficiency and the light extraction efficiency. The internal quantum efficiency of LED was already reached to more than 90%, but the light extraction efficiency is still insufficient compared with the internal quantum efficiency because the total internal reflection is generated in the interface between the LED chip and air. Thus, we studied about flip chip LED with PSS and performed the optical simulation which find more optimized PSS for flip chip LED to increase the light extraction efficiency. Decreasing of the total internal reflection and effect of diffused reflection according to PSS improved the light extraction efficiency. To get more higher the efficiency, we simulated flip chip with PSS that the parameters are arrangement, edge spacing, radius, height and shape of PSS.

• Journal of the Optical Society of Korea
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• 제18권6호
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• pp.772-776
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• 2014

We report a numerical analysis of the light-extraction efficiency (LEE) of light-emitting diodes (LEDs) on patterned sapphire substrates (PSSs). We considered various n-sided, regular convex pyramids, where n is an integer and $n{\geq}3$. We then considered four cross sections: extruded, subtracted, truncated-extruded, and truncated-subtracted. Ray-tracing simulations were carried out with these polygonal pyramid patterns, and the dimensions of the patterns were systematically varied. Optimized pattern shapes were determined for large LEE. An extruded circular pyramid with a slant angle of $45^{\circ}$ was found to be the optimal patterned shape.

• 한국결정성장학회지
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• 제29권4호
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• pp.173-178
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• 2019

본 연구에서는 halide vapor phase epitaxy 성장법을 이용하여 원뿔 형태의 패턴이 주기적으로 형성된 patterned sapphire substrate(PSS) 위에 ${\alpha}-Ga_2O_3$를 성장하고 그 특성에 변화에 대해 분석하였다. PSS의 패턴의 유무에 따른 영향을 알아보기 위해 c-plane 사파이어 기판과 원뿔의 크기가 다른 두 개의 PSS 위에 ${\alpha}-Ga_2O_3$를 성장하여 비교 분석하였다. 또한 PSS 위에 성장된 ${\alpha}-Ga_2O_3$의 성장과정을 알아보기 위해 점차 성장 시간을 증가해가며 관찰하였고 성장 온도를 $470-550^{\circ}C$까지 변화해가며 성장하였다. 이를 통해 원뿔 형태의 패턴이 형성된 PSS 위에서의 최적 성장 조건과 그 성장 mechanism에 대해 분석이 가능하였고 그 결과로 성장과정에서 발생하는 수평 성장에 의해 ${\alpha}-Ga_2O_3$의 비대칭면인 (10-14) 반치폭 값을 크게 감소시킬 수 있었다.

• 한국결정성장학회지
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• 제30권1호
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• pp.1-6
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• 2020

본 연구에서는 패턴화된 사파이어 기판 위에 HVPE(Hydride Vapor Phase Epitaxy System) 법에 의해 50 nm 두께의 AlN thin film을 증착한 뒤, 에피층 구조가 MO CVD에서 성장되었다. AlN 버퍼층 박막의 표면형상이 SEM, AFM에 의해서, 에피층 구조의 GaN 박막의 결정성은 X-선 rocking curve에 의해 분석되었다. 패턴화된 사파이어 기판 위에 증착된 GaN 박막은, 사파이어 기판 위에 증착된 GaN 박막의 경우보다 XRD 피크 세기가 다소 높은 결과를 나타냈다. AFM 표면 형상에서 사파이어 기판 위에 AlN 박막이 증착된 경우, GaN 에피층 박막의 p-side 쪽의 v-pit 밀도가 상대적으로 낮았으며, 결함밀도가 낮게 관찰되었다. 또한, AlN 버퍼층이 증착된 에피층 구조는 AlN 박막이 없는 에피층의 광출력에 비해 높은 값을 나타냈다.