• 전자공학회논문지
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• 제53권9호
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• pp.129-134
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• 2016

본 논문은 허상 디스플레이의 광원으로 적용되는 고휘도 레이저의 접합온도에 따른 파장 변이(an optical quenching) 제어와 광 출력 효율 증대를 위한 제어 방법에 대해 연구하였다. 차량용 헤드업 디스플레이(Head-up Display)와 같은 허상 디스플레이(Virtual Display)는 외부 조도 환경의 영향을 받는 디스플레이 특성으로 인하여 디스플레이 휘도와 광효율 측면의 기술요소에 대한 해결 방법이 요구된다. 태양광의 영향으로 인하여 헤드업 디스플레이는 고휘도 광원에 대한 필요가 증대되고 있으며, 이러한 문제점을 해결하기 위하여 고휘도 청색 레이저 광원이 검토되고 있다. 그러나 낮은 레이저 접합 온도 특성의 단점을 갖고 있어 수명 감소와 광효율 감소라는 문제점을 지니고 있으며 특히 청색 파장 변이를 일으키는 원인이 된다. 이러한 문제점을 해결하기 위하여 고주파 펄스폭 변조 방식의 전류인가 방법과 황색 형광 물질을 사용한 칼라 휠 방식의 DMD(digital micro mirror device) 초소형 패널을 적용하였다. 적응형 펄스폭 변조 방식의 주파수와 듀티비 분석과 최적화를 통하여 청색 레이저의 파장 변이를 방지하고 37%의 광효율을 증대 효과를 얻었다.

• 반도체디스플레이기술학회지
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• 제16권4호
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• pp.86-90
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• 2017

$Tb^{3+}$ or $Eu^{3+}$ or $Ce^{3+}$-doped $CaYAlO_4$ phosphor were synthesized by solid-state method. $CaYAlO_4:Tb^{3+}$ is shown that the $Tb^{3+}$-doping concentration has a significant effect on the $^5D_4/^5D_3{\rightarrow}7F_J$ (J=6,...,0) emission intensity of $Tb^{3+}$. The $CaYAlO_4:Tb^{3+}$ phosphors show tunable photoluminescence from blue to yellow with the change of doping concentration of $Tb^{3+}$ ions. The $CaYAlO_4:Eu^{3+}$ phosphors exhibit a red-orange emission of $Eu^{3+}$ corresponding to $^5D_0$, $_{1,2}{\rightarrow}^7F_J$ (J=4,...,0) transitions. The $CaYAlO_4:Ce^{3+}$ phosphors show a blue emission due to $Ce^{3+}$ ions transitions from the 5d excited state to the $^2F_{5/2}$ and $^2F_{7/2}$ ground states. The decay time of $CaYAlO_4:Tb^{3+}$ phosphors decrease from 1.33 ms to 0.97 ms as $Tb^{3+}$ concentration increases from 0.1 mol% to 7 mol%. The decay time of $CaYAlO_4:Eu^{3+}$ phosphors increase from 0.94 ms to 1.17 ms as $Eu^{3+}$ concentration increases from 1 mol% to 9 mol%.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.