• 한국진공학회지
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• 제9권3호
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• pp.227-232
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• 2000

광소자와 마이크로파 유전체 소자 및 절연 산화막으로의 응용을 위한 $MgTiO_3$ 박막을 펄스레이저 증착법을 이용하여 다양한 기판 위에서 증착하였다. 사파이어 기판에(c-plane Sapphire) 성장된 $MgTiO_3$ 박막은 에피텍셜 성장(epitaxial growth)이 되었으며, $SiO_2$/Si 및 Pt/Ti/$SiO_2$/Si(plantinzed silicon)기판 위에 성장된 $MgTiO_3$ 박막의 경우, 기판과 관계없이 c축 방향으로 배향(oriented)되었다. 사파이어 기판 위에 증착된 $MgTiO_3$ 박막은 가시영역에서 투명하였으며, 약 290 nm 파장을 갖는 영역에서 급격한 흡수단을 보였다. 사파이어 기판 위에 성장된 박막의 AM(Atomic Force Microscopy)분석결과 약 0.87 nm rms roughness 값을 갖는 매우 평탄한 표면상태를 갖고 있음을 확인하였다. MIM(Pt/$MgTiO_3$/Pt) 구조의 캐패시터를 형성시켜 $MgTiO_3$박막의 유전특성 (dielectric properties)을 관찰하였는데, 펄스레이저 증착법으로 성장된 $MgTiO_3$ 박막의 유전율(relative dielectric constant)은 약 24.5였으며, 1 MHz에서 약 1.5%의 유전손실(dielectric loss) 값을 보였다. 또한 이때 $MgTiO_3$박막은 낮은 유전분산을 보였다.

• 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.

• 대한원격탐사학회지
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• 제37권6_1호
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• pp.1631-1645
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• 2021

세계 최초 능동형 라이더 센서 Atmospheric Laser Doppler Instrument (ALADIN)의 바람 자료와 한국형 수치예보모델에 바람 자료로 활용되고 있는 Geostationary Korea Multi Purpose Satellite 2A (GK2A)의 대기운동벡터의 자료를 비교함으로써 두 위성의 바람 자료의 특징을 분석하였다. 2019년 9월부터 20220년 8월 1년의 자료를 ALADIN의 미(Mie)채널과 GK2A 적외채널에 대하여 비교한 결과 수집된 자료는 177,681개이며 평균 제곱근 오차(Root Mean Square Error; RMSE)는 3.73 m/s, 상관계수는 0.98이다. 상세한 분석을 위해 위도와 고도를 고려하여 비교한 결과, 대부분의 위도에서 표준화된 평균 제곱근 오차(Normalized Root Mean Squared Error; NRMSE)가 0.2~0.3으로 두 바람 자료가 일치하지만 상층, 중층의 경우 저위도지역에서, 하층의 경우 남반구 특정 위도(30°S-15°S)에서 0.4 이상으로 큰 값을 가진다. 이러한 결과는 계절에 상관없이 수증기채널, 가시채널에서도 동일하게 나타나며 채널 별 특징과 계절별 특징은 두드러지게 나타나지 않는다. 두 바람 자료 간에 차이가 큰 위도 영역에 대하여 구름의 분포를 확인해본 결과, 대기운동벡터의 고도 할당 정확도를 낮출 수 있는 권운 이나 적운이 다른 위도에 비해 더 많이 분포하고 있다. 이러한 특성에 따라, 정확한 고도 할당이 어려워 대기운동벡터의 오차가 크게 나타나는 남반구와 저위도 영역에서 ALADIN 바람 자료는 기존 대기운동벡터의 바람 정보를 보완함으로써 수치예보모델에 긍정적인 영향을 미칠 수 있음을 제시한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.31-31
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• 2010

The growth of the high-quality GaN epilayers is of significant technological importance because of their commercializedoptoelectronic applications as high-brightness light-emitting diodes (LEDs) and laser diodes (LDs) in the visible and ultraviolet spectral range. The GaN-based heterostructural epilayers have the polar c-axis of the hexagonal structure perpendicular to the interfaces of the active layers. The Ga and N atoms in the c-GaN are alternatively stacked along the polar [0001] crystallographic direction, which leads to spontaneous polarization. In addition, in the InGaN/GaN MQWs, the stress applied along the same axis contributes topiezoelectric polarization, and thus the total polarization is determined as the sum of spontaneous and piezoelectric polarizations. The total polarization in the c-GaN heterolayers, which can generate internal fields and spatial separation of the electron and hole wave functions and consequently a decrease of efficiency and peak shift. One of the possible solutions to eliminate these undesirable effects is to grow GaN-based epilayers in nonpolar orientations. The polarization effects in the GaN are eliminated by growing the films along the nonpolar [$11\bar{2}0$] ($\alpha$-GaN) or [$1\bar{1}00$] (m-GaN) orientation. Although the use of the nonpolar epilayers in wurtzite structure clearly removes the polarization matters, however, it induces another problem related to the formation of a high density of planar defects. The large lattice mismatch between sapphiresubstrates and GaN layers leads to a high density of defects (dislocations and stacking faults). The dominant defects observed in the GaN epilayers with wurtzite structure are one-dimensional (1D) dislocations and two-dimensional (2D) stacking faults. In particular, the 1D threading dislocations in the c-GaN are generated from the film/substrate interface due to their large lattice and thermal coefficient mismatch. However, because the c-GaN epilayers were grown along the normal direction to the basal slip planes, the generation of basal stacking faults (BSFs) is localized on the c-plane and the generated BSFs did not propagate into the surface during the growth. Thus, the primary defects in the c-GaN epilayers are 1D threading dislocations. Occasionally, the particular planar defects such as prismatic stacking faults (PSFs) and inversion domain boundaries are observed. However, since the basal slip planes in the $\alpha$-GaN are parallel to the growth direction unlike c-GaN, the BSFs with lower formation energy can be easily formed along the growth direction, where the BSFs propagate straightly into the surface. Consequently, the lattice mismatch between film and substrate in $\alpha$-GaN epilayers is mainly relaxed through the formation of BSFs. These 2D planar defects are placed along only one direction in the cross-sectional view. Thus, the nonpolar $\alpha$-GaN films have different atomic arrangements along the two orthogonal directions ($[0001]_{GaN}$ and $[\bar{1}100]_{GaN}$ axes) on the $\alpha$-plane, which are expected to induce anisotropic biaxial strain. In this study, the anisotropic strain relaxation behaviors in the nonpolar $\alpha$-GaN epilayers grown on ($1\bar{1}02$) r-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVO) were investigated, and the formation mechanism of the abnormal zigzag shape PSFs was discussed using high-resolution transmission electron microscope (HRTEM).