• 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.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.51-51
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• 2010

Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

• 한국광학회지
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• 제19권5호
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• pp.381-385
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• 2008

InGaN/Sapphire LED에서 기판 제거와 패키지 방식이 광출력 특성에 미치는 영향을 분석하였다. Sapphire 기판의 제거는 반도체 접합에서 발생된 열의 방출에 도움이 되지만, 반대로 광추출효율이 손상되는 문제점이 수반된다. Sapphire 기판이 제거된 칩을 열전도율이 좋은 금속의 마운트 위에 부착하면, 최대 구동전류는 현저히 증가하고 광출력도 상당히 증가됨으로써, 광추출효율이 손상되는 문제점이 어느 정도 보상된다. 하지만, sapphire 기판이 제거된 칩을 상대적으로 열전도율이 낮은 유전체의 마운트 위에 부착하는 경우에는, 거의 모든 입력전류 범위에서 sapphire 기판이 남아 있는 일반형 칩보다 낮은 광출력을 나타낸다. 따라서, 작은 광출력이 요구되는 응용분야에서는 사용된 칩 마운트의 종류에 무관하게, 일반형 칩이 sapphire 기판이 제거된 칩 보다 유리한 것으로 분석된다.

• 전자공학회논문지D
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• 제35D권8호
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• pp.24-30
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• 1998

A blue LED of $In_{x}Ga_{1-x}N$ multiple quantum well structure which had the blue emission spectrum of donor-acceptor pair transition generated form Si-Zn co-doped $In_{x}Ga_{1-x}N$ active layer, was fabricated. The $In_{x}Ga_{1-x}N$ MQW heterojunction LED structure was grown by MOCVD on the sapphire substrate with (0001) surface orientation at 800.deg. C. The fabricated LED exhibited forward cut-in voltage of 4~4.5V and reverse breakdown voltage of -13V. Its optical chracteristics showed that the center wavelength of peak emission occurred at 460nm and the optical intensity was increased linearly with respect to the injected electrical current above 5mA.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.279.2-279.2
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• 2016

InGaN/GaN multiple quantum wells (MQWs) have been attracted much attention as light-emitting diodes (LEDs) in the visible and UV regions. Particularly, quantum efficiency of green LEDs is decreased dramatically as approaching to the green wavelength (~500 nm). This low efficiency has been explained by quantum confined Stark effect (QCSE) induced by piezoelectric field caused from a large lattice mismatch between InGaN and GaN. To improve the quantum efficiency of green LED, several ways including epitaxial lateral overgrowth that reduces differences of lattice constant between GaN and sapphire substrates, and non-polar method that uses non- or semi-polar substrates to reduce QCSE were proposed. In this study, graded short-period InGaN/GaN superlattice (GSL) was grown below the 5-period InGaN/GaN MQWs. InGaN/GaN MQWs were grown on the patterned sapphire substrates by vertical-metal-organic chemical-vapor deposition system. Five-period InGaN/GaN MQWs without GSL structure (C-LED) were also grown to compare with an InGaN/GaN GSL sample. The luminescence properties of green InGaN/GaN LEDs have been investigated by using photoluminescence (PL) and time-resolved PL (TRPL) measurements. The PL intensities of the GSL sample measured at 10 and 300 K increase about 1.2 and 2 times, respectively, compared to those of the C-LED sample. Furthermore, the PL decay of the GSL sample measured at 10 and 300 K becomes faster and slower than that of the C-LED sample, respectively. By inserting the GSL structures, the difference of lattice constant between GaN and sapphire substrates is reduced, resulting that the overlap between electron and hole wave functions is increased due to the reduced piezoelectric field and the reduction in dislocation density. As a results, the GSL sample exhibits the increased PL intensity and faster PL decay compared with those for the C-LED sample. These PL and TRPL results indicate that the green emission of InGaN/GaN LEDs can be improved by inserting the GSL structures.

• ETRI Journal
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• 제35권4호
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• pp.566-570
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• 2013

In this paper, we demonstrate the capabilities of 380-nm ultraviolet (UV) light-emitting diodes (LEDs) using metal organic chemical vapor deposition. The epi-structure of these LEDs consists of InGaN/AlGaN multiple quantum wells on a patterned sapphire substrate, and the devices are fabricated using a conventional LED process. The LEDs are packaged with a type of surface mount device with Al-metal. A UV LED can emit light at 383.3 nm, and its maximum output power is 118.4 mW at 350 mA.

• 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.

• Transactions on Electrical and Electronic Materials
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• 제10권2호
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• pp.40-43
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• 2009

The authors fabricated a nanopatterned surface on a GaN thin film deposited on a sapphire substrate and used that as an epitaxial wafer on which to grow an InGaN/GaN multi-quantum well structure with metal-organic chemical vapor deposition. The deposited GaN epitaxial surface has a two-dimensional photonic crystal structure with a hexagonal lattice of 230 nm. The grown structure on the nano-surface shows a Raman shift of the transverse optical phonon mode to $569.5\;cm^{-1}$, which implies a compressive stress of 0.5 GPa. However, the regrown thin film without the nano-surface shows a free standing mode of $567.6\;cm^{-1}$, implying no stress. The nanohole surface better preserves the strain energy for pseudo-morphic crystal growth than does a flat plane.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.314.2-314.2
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• 2014

To improve the optical and electrical properties of commercialized GaN-based light-emitting diodes (LEDs), many methods are suggested. In recent years, great efforts have been made to improve the internal quantum efficiency and light extraction efficiency (LEE) and promising approaches are suggested using a patterned sapphire substrate (PSS), V-pit embedded LED structures, and silica nanostructures. In this study, we report on the enhancement of photoluminescence (PL) intensity in GaN-based LED structures by using the combination of SiO2 (silica) nanospheres and polystyrene/SiO2 core-shell nanospheres. The SiO2 nanospheres-coated LED structure shows the slightly increased PL intensity. Moreover the polystyrene/SiO2 core-shell nanospheres-coated structure shows the more increase of PL intensity comparing to that of only SiO2 spheres-coated structure and the conventional structure without coating of nanospheres. The Finite-difference time-domain (FDTD) simulation results show corresponding result with experimentally observed results. The mechanism of enhancement of PL intensity using the coating of polystyrene/SiO2 core-shell nanospheres on LED surface can be explained by the improvement in extraction efficiency by both increasing the probability of light escape by reducing Fresnel reflection and by multiple scattering within the core-shell nanospheres.

• 한국광학회지
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• 제22권3호
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• pp.141-150
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• 2011

현재까지 더 좋은 성능의 LED 램프 패키지 구조의 개발을 위해 많은 연구가 진행되어 왔음에도 불구하고 아직 LED 램프 패키지 설계에 관한 표준화된 이론이나 지침 같은 것들이 마련되지 못한 것으로 판단된다. 이에 본 논문에서는 먼저 Monte Carlo photon simulation 기법을 이용하여 InGaN/Sapphire LED의 칩 구조 및 Epi-up 혹은 Epi-down 칩 부착 방식을 광추출효율 관점에서 분석하였다. 그리고 분석결과를 바탕으로 LED 램프 패키지 설계에 관한 기본 지침을 마련하였다. 이와 같이 마련된 설계지침은 관련 기업이나 연구기관에서, LED 램프의 구체적 응용분야에 따라 최적화된 패키지 구조를 설계하는 데에 중요하게 활용될 수 있을 것으로 기대된다.