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HVPE 법을 통한 GaN 성장 시 기판 종류 및 V/III 비에 따른 잔류 stress 특성 연구
이주형,이승훈,이희애,강효상,오누리,이성철,이성국,박재화,Lee, Joo Hyung,Lee, Seung Hoon,Lee, Hee Ae,Kang, Hyo Sang,Oh, Nuri,Yi, Sung Chul,Lee, Seong Kuk,Park, Jae Hwa 한국결정성장학회 2020 한국결정성장학회지 Vol.30 No.2
본 연구에서는 HVPE 성장법으로 GaN 성장 시 GaN 내에 잔류하는 stress로 인한 crack 현상을 감소시키고자 기판 종류 및 V/III 비를 조절하여 잔류 stress 특성을 알아보고자 하였다. Sapphire, GaN template 위에 각각 V/III 비 5, 10, 15의 조건으로 GaN을 성장시켜 형성된 hexagonal pit의 분포 및 깊이를 분석하였다. 이를 통해 GaN on GaN template 성장에서 V/III 비가 높을수록 hexagonal pit의 분포 영역 및 깊이가 증가하는 것을 확인하였다. Raman 측정을 통해 hexagonal pit 영역 및 깊이가 컸던 GaN on GaN template 성장에서 V/III 비가 높을수록 stress가 감소하는 것을 확인하였다. 이를 통해 hexagonal pit의 분포 및 깊이가 증가할수록 잔류 stress가 낮아짐을 확인할 수 있었으며, 향후 후막 GaN 성장 시 stress 감소 가능성에 대해 확인하였다. The characteristics of the residual stress on the types of the substrate was investigated with adjusting the V/III ratio during GaN growth via the HVPE method. GaN single crystal layers were grown on a sapphire substrate and a GaN template under the conditions of V/III ratio 5, 10, and 15, respectively. During GaN growth, multiple hexagonal pits in GaN single crystal were differently revealed in accordance with growth condition and substrate type, and their distribution and depth were measured via optical microscopy(OM) and white light interferometry(WLI). As a result, it was confirmed that the distribution area and depth of hexagonal pit tended to increase as the V/III ratio increased. Moreover, it was found that the residual stress in GaN single crystal decreased as the distribution area and depth of the pit increased through measuring micro Raman spectrophotometer. In the case of GaN growth according to substrate type, the GaN on GaN template showed lower residual stress than the GaN grown on sapphire substrate.
Reduction of Leakage Current in InGaN-based LEDs with V-pit Embedded Structures
박진섭,하준석 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
We investigated the effects of V-pit structures embedded in the active region of n-GaN on leakage current and emission efficiency in InGaN/GaN light-emitting diodes (LEDs). Size-controlled V-pits were used for dislocation filtering. The V-shaped pit size was controlled by manipulating the growth temperature and pressure. The highest reverse voltage values were achieved with 150-nm-sized V-pit-embedded LEDs, which can be attributed to the effective blocking of the threading dislocations acting as a leakage current source.
Correlation between pit formation and phase separation in thick InGaN film on a Si substrate
Woo, Hyeonseok,Jo, Yongcheol,Kim, Jongmin,Cho, Sangeun,Roh, Cheong Hyun,Lee, Jun Ho,Kim, Hyungsang,Hahn, Cheol-Koo,Im, Hyunsik ELSEVIER 2018 CURRENT APPLIED PHYSICS Vol.18 No.12
<P><B>Abstract</B></P> <P>We demonstrate improved surface pit and phase separation in thick InGaN grown on a GaN/Si (111) substrate, using plasma-assisted molecular beam epitaxy with an indium modulation technique. The formation of surface pit and compositional inhomogeneity in the InGaN epilayer are investigated using atomic force microscopy, scanning electron microscopy and temperature-dependent photoluminescence. Indium elemental mapping directly reveals that poor compositional homogeneity occurs near the pits. The indium-modulation epitaxy of InGaN minimizes the surface indium segregation, leading to the reduction in pit density and size. The phase separation in InGaN with a higher pit density is significantly suppressed, suggesting that the pit formation and the phase separation are correlated. We propose an indium migration model for the correlation between surface pit and phase separation in InGaN.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High-quality thick epi-InGaN is grown on a GaN/Si (111) substrate. </LI> <LI> The phase separation near the threading dislocation is associated with surface indium migration. </LI> <LI> The IME technique with a pulse-patterned indium supply provides an optimal surface condition. </LI> </UL> </P>
Correlation between pit formation and phase separation in thick InGaN film on a Si substrate
우현석,조용철,김종민,조상은,노정현,이준호,김형상,한철구,임현식 한국물리학회 2018 Current Applied Physics Vol.18 No.12
We demonstrate improved surface pit and phase separation in thick InGaN grown on a GaN/Si (111) substrate, using plasma-assisted molecular beam epitaxy with an indium modulation technique. The formation of surface pit and compositional inhomogeneity in the InGaN epilayer are investigated using atomic force microscopy, scanning electron microscopy and temperature-dependent photoluminescence. Indium elemental mapping directly reveals that poor compositional homogeneity occurs near the pits. The indium-modulation epitaxy of InGaN minimizes the surface indium segregation, leading to the reduction in pit density and size. The phase separation in InGaN with a higher pit density is significantly suppressed, suggesting that the pit formation and the phase separation are correlated. We propose an indium migration model for the correlation between surface pit and phase separation in InGaN.
Dong Hoon Shin,Sang-Yuck Shim,Myeung Ju Kim,Chang Seok Oh,Mi-Hyun Lee,Suk Bae Jung,Geon Il Lee,Jong-Yil Chai,Min Seo 대한기생충학열대의학회 2014 The Korean Journal of Parasitology Vol.52 No.5
In a paleo-parasitological analysis of soil samples obtained from V-shaped pits dating to the ancient Baekje period in Korean history, we discovered Ascaris lumbricoides, Trichuris trichiura, and Clonorchis sinensis eggs. In light of the samples’ seriously contaminated state, the V-shaped pits might have served as toilets, cesspits, or dung heaps. For a long period of time, researchers scouring archaeological sites in Korea have had difficulties locating such structures. In this context then, the present report is unique because similar kind of the ancient ruins must become an ideal resource for successful sampling in our forthcoming paleoparasitological studies.
고각 환형 암시야 주사투과전자현미경기법과 투과전자현미경기법을 이용한 상용 청색 발광다이오드의 종합적인 구조분석
김동엽,홍순구,정태훈,이상헌,백종협,Kim, Dong-Yeob,Hong, Soon-Ku,Chung, Tae-Hoon,Lee, Sang Hern,Baek, Jong Hyeob 한국재료학회 2015 한국재료학회지 Vol.25 No.1
This study suggested comprehensive structural characterization methods for the commercial blue light emitting diodes(LEDs). By using the Z-contrast intensity profile of Cs-corrected high-angle annular dark field scanning transmission electron microscope(HAADF-STEM) images from a commercial lateral GaN-based blue light emitting diode, we obtained important structural information on the epilayer structure of the LED, which would have been difficult to obtain by conventional analysis. This method was simple but very powerful to obtain structural and chemical information on epi-structures in a nanometer-scale resolution. One of the examples was that we could determine whether the barrier in the multi-quantum well(MQW) was GaN or InGaN. Plan-view TEM observations were performed from the commercial blue LED to characterize the threading dislocations(TDs) and the related V-pit defects. Each TD observed in the region with the total LED epilayer structure including the MQW showed V-pit defects for almost of TDs independent of the TD types: edge-, screw-, mixed TDs. The total TD density from the region with the total LED epilayer structure including the MQW was about $3.6{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion as 80%: 7%: 13%. However, in the mesa-etched region without the MQW total TD density was about $2.5{\times}10^8cm^{-2}$ with a relative ratio of Edge- : Screw- :Mixed-TD portion of 86%: 5%: 9 %. The higher TD density in the total LED epilayer structure implied new generation of TDs mostly from the MQW region.
HVPE 법에서의 공정변수 조절에 의한 bulk GaN 단결정의 두께 최적화
박재화,이희애,이주형,박철우,이정훈,강효상,강석현,방신영,이성국,심광보,Park, Jae Hwa,Lee, Hee Ae,Lee, Joo Hyung,Park, Cheol Woo,Lee, Jung Hun,Kang, Hyo Sang,Kang, Suk Hyun,Bang, Sin Young,Lee, Seong Kuk,Shim, Kwang Bo 한국결정성장학회 2017 韓國結晶成長學會誌 Vol.27 No.2
다양한 성장온도, V/III 비율, 성장속도과 같은 공정변수의 조절을 통하여 GaN 단결정을 성장시키고, 그에 따른 표면 및 재료 내부의 결함분석을 통하여 고휘도 고출력의 소자적용을 위한 bulk GaN 단결정의 두께를 최적화하였다. 2인치 직경의 sapphire 기판 위에 HVPE(hydride vapor phase epitaxy) 공정변수들을 조절하여, 0.3~7.0 mm 두께의 GaN 결정을 성장시켰다. 성장된 GaN 단결정의 구조분석을 위하여 XRD 분석을 사용하였고, 공정변수의 변화에 따른 표면 특성은 광학 현미경을 이용하여 관찰하였다. 성장된 두께에 따른 결함밀도 분석을 위하여 화학습식 에칭하였고, 에칭된 표면을 SEM으로 관찰하였다. GaN single crystals were grown by controlling of various processing parameters such as growing temperature, V/III ratio and growing rate. We optimized thickness of bulk GaN single crystal by analyzing defect of surface and inside of the GaN single crystal for application to high brightness and power device. 2-inch bulk GaN single crystals were grown by HVPE (hydride vapor phase epitaxy) on sapphire and their thickness was 0.3~7.0 mm. Crystal structure of the grown bulk GaN was analyzed by XRD (X-ray diffraction). The surface characteristics of the grown bulk GaN were observed by OM (optical microscope) and SEM (scanning electron microscopy) with measuring EPD (etch pits density) of the GaN crystals.
Numerical Simulation on Energy Concentration and Release Process of Strain Rockburst
Ang Lu,Peng Yan,Wenbo Lu,Ming Chen,Gaohui Wang,Sheng Luo,Xiao Liu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.10
Rockburst mechanism has been a hot topic in the stability analysis of underground carven excavation, and the accurate description of energy evolution process is very critical to rockburst prediction. To study the evolution process of rockburst, such as V-shaped rockburst pit, theoretical formula derivation and numerical simulation are adopted to research the dynamic response characteristics during the formation process of rockburst pits quantitatively. The results show that rockburst intensity distribution varies with failure depth. It can be divided into three zone: slow-increase, rapid-increase and slow-decrease. For a circular tunnel with radius R, the strain energy release rate and vibration response of surrounding rock increases gradually within (0 − 0.06) R; reaches the peak value around (0.06 − 0.1) R and drops to a balance beyond 0.1R. Due to the same law of them, the rockburst risk can be conveniently predicted by monitoring vibration of surrounding rock with a certain depth. This work is beneficial to provide a good reference for rockburst prediction.