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남기웅,김병구,임재영,Dong Yul Lee,김종수,김진수 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.9
The effect of an electron blocking layer (EBL) on the V − I curves for GaN/InGaN multiplequantum wells is investigated. For the first time, we found that the curves intersected at 3.012 V,and we investigated the reason for the intersection. The forward voltage in LEDs with a p-AlGaNEBL is larger than it is without the p-AlGaN EBL at low injection currents because the Mg-dopingefficiency for the p-GaN layer is higher than that for the p-AlGaN layer. However, the forwardvoltage in LEDs with a p-AlGaN EBL is smaller than it is without the p-AlGaN EBL at highinjection currents because the carriers overflow from the active layer when the injection currentincreases in LEDs without a p-AlGaN EBL, in case of LEDs with a p-AlGaN EBL, the carriers areblocked by the EBL.
남기웅,김성수,조의제,김경제,임재영,손정식,김성오 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.1
In this study, we fabricated high-quality ZnO films using hydrothermally grown ZnO nanorods and a spin-coated Al-doped ZnO film by using regrowth method. The phtoluminescence (PL) intensity ratios of the near-band-edge (NBE) to deep-level (DL) emission peaks (INBE/IDL) for ZnO nanorods (samples 1) and ZnO film (sample 2) were 2.13 and 24.3, respectively. The redshift from 3.288 (sample 2) to 3.278 eV (sample 1) and low INBE/IDL ratio in PL spectra were attributed to large mismatch between ZnO and Si substrate, resulting in a residual stress and the low optical properties. In case of sample 2, the photocurrent was sharply increased without the exponential rise because of enhanced optical properties of ZnO film by regrowth. The regrowth method is expected to represent a possible route for fast-response ultraviolet sensors.
Growth of ZnO Soccer Ball Structures by Using Vapor Phase Transport
남기웅,임재영,김소아람,김민수,임광국,Do Yeob Kim,Sung-O Kim 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.1
Zinc oxide (ZnO) was grown on a Au-catalyzed Si(100) substrate by using a simple vapor phase transport (VPT) with a mixture of zinc oxide and graphite powders. The ZnO grown at 800 ℃ had a soccer ball structure with diameters of <500 nm. The ZnO soccer ball structure was, for the first time, observed in this work. The structural and the optical properties of the ZnO soccer balls were investigated by using field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence. The preferred orientation of the ZnO soccer balls was along the c-axis with a hexagonal wurtzite structure. The ZnO soccer balls exhibited an overall tensile residual stress, and the bond length of Zn-O was 1.951 Å. In the room-temperature PL of the ZnO soccer balls, a near-band-edge emission (NBE) and a deep-level emission were observed at 3.25 and 2.47 eV, respectively. The full width at half maximum of the NBE peak was 110 meV.
남기웅,편정민,권형민 대한신경과학회 2016 대한신경과학회지 Vol.34 No.4
The prognosis of lateral medullary infarction is mostly benign, but unexpected sudden death can occur even when the initial symptoms are benign. An 81-year-old man visited the emergency room with whirling-type dizziness and right-veering tendency. Brain magnatic resonance imaging (MRI) revealed a right lateral medullary infarction accompanied by a right cerebellar infarction. He died suddenly at 1 day after admission with only slight lesion progression on MRI. This case suggests that patients with a lateral medullary infarction should be carefully monitored during the acute period.