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Woo, Hyeonseok,Kim, Jongmin,Cho, Sangeun,Jo, Yongcheol,Roh, Cheong Hyun,Lee, Jun Ho,Seo, Yong Gon,Kim, Hyungsang,Im, Hyunsik,Hahn, Cheol-Koo Elsevier 2018 Superlattices and microstructures Vol.120 No.-
<P><B>Abstract</B></P> <P>An effective method for high-quality molecular beam epitaxy growth of InGaN/GaN multiple quantum wells is demonstrated by inserting an ultrathin low temperature GaN (LT-GaN) interlayer between InGaN well and conventional high temperature GaN (HT-GaN) barrier layers. The LT-GaN interlayer is fabricated using metal migration enhanced epitaxy at the same growth temperature for InGaN. A smooth LT-GaN surface with a low defect density is obtained and indium decomposition is not observed. Large emission blueshift is significantly suppressed and narrow linewidth photoluminescence emission is achieved. The improved optical properties of the InGaN/GaN MQWs with LT-GaN interlayers are due to reduced compositional fluctuation and improved interface roughness.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High quality epi-GaN is grown at a low temperature (590 °C) using metal migration enhanced MBE epitaxy. </LI> <LI> Surface roughness and defect density of low-temperature GaN are considerably improved. </LI> <LI> InGaN/GaN QWs with low-temperature epi-GaN insertion show significantly suppressed indium decomposition and single PL peak. </LI> </UL> </P>
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>
Effect of heating on electrical transport in AlGaN/GaN Schottky barrier diodes on Si substrate
Woo, Hyeonseok,Jo, Yongcheol,Kim, Jongmin,Roh, Cheonghyun,Lee, Junho,Kim, H.,Im, H.,Hahn, Cheol-koo,Park, Jungho Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.1
Thermal properties of the AlGaN/GaN Schottky barrier diodes were investigated, using a pulsed-IV measurement technique. The thermally degraded mobility in the DC-bias configuration was restored, when the pulse-bias voltages were applied. It was observed that heat generation was minimized, using a pulse width of 500 ns and pulse period of 10 ms. For the SBDs consisting of 5 mu m of anode-cathode distance, on-resistance measured by the pulse-IV and DC-IV were 1.6 and 6.2 Omega-mm, respectively. We also demonstrated the device-width dependence of the thermal properties of the SBDs. We found that the performance of the power devices can be greatly influenced by the heat generation. (C) 2013 Elsevier B.V. All rights reserved.
Woo, Hyeonseok,Kim, Jongmin,Cho, Sangeun,Jo, Yongcheol,Roh, Cheong Hyun,Kim, Hyungsang,Hahn, Cheol-Koo,Im, Hyunsik The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3
An InGaN/GaN multiple quantum well (MQW) structure is grown on a GaN/sapphire template using a plasma-assisted molecular beam epitaxy (PA-MBE). The fluctuation of the quantum well thickness formed from roughly-grown InGaN layer results in a disordered photoluminescence (PL) spectrum. The surface morphologies of the InGaN layers with various In compositions are investigated by reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). A blurred InGaN/GaN hetero-interface and the non-uniform QW size is confirmed by high resolution transmission electron microscopy (HR-TEM). Inhomogeneity of the quantum confinement results in a degradation of the quantum efficiency even though the InGaN layer has a uniform In composition.
Comparison of adverse drug reaction profiles of two tacrolimus formulations in rats
Hwang, HyeonSeok,Ghee, Jung Yeon,Song, Ji Hyun,Piao, ShangGuo,Yang, Chul Woo Informa Healthcare 2012 IMMUNOPHARMACOLOGY AND IMMUNOTOXICOLOGY Vol.34 No.3
<P>Tacrobell<SUP>®</SUP> (TB) is a generic tacrolimus which showed the comparable efficacy to original product, Prograf<SUP>®</SUP> (PG) in renal transplantation, but toxicity between two drugs is unclear. The aim of this study was to compare the toxicity between these two formulations. TB and PG (0.5, 1 and 2 mg/kg/day) was administered to rats for 4 weeks. The rat survival rate, kidney, liver and pancreas injury was investigated. The survival rate was similar between TB- and PG-treated rats. TB and PG induced renal dysfunction in a dose-dependent manner. Compared to PG treatment in equal dose, TB treatment reduced urinary creatinine clearance in a less degree and renal interstitial fibrosis was comparable between two regimens. The r-glutamyl transpeptidase was aggravated by tacrolimus treatment, and this was not different between TB and PG treatment. In the intraperitoneal glucose tolerance test, a significant diabetogenic effect was observed in all tacrolimus treated-rats. The glucose tolerance of TB-treated rats was similar to those of PG-treated rats in each dose. The decrement in pancreatic β-cell mass by tacrolimus showed the dose-dependent response and it was comparable between TB and PG treatment. In conclusion, TB is similar to PG in terms of nephrotoxicity, hepatoxicity and diabetogenic effect.</P>
A Systematic Review of Herbal Medicine for Chemotherapy Induced Peripheral Neuropathy
Noh, Hyeonseok,Yoon, Seong Woo,Park, Bongki Hindawi 2018 Evidence-based Complementary and Alternative Medic Vol.2018 No.-
<P><B>Background</B></P><P> Chemotherapy-induced peripheral neuropathy (CIPN) is a common adverse effect in cancer patients. The aim of this review was to assess the effectiveness of herbal medicine in preventing and treating CIPN.</P><P><B> Methods</B></P><P> Randomised controlled trials were included in this review. Extracting and assessing the data independently, two authors searched 13 databases.</P><P><B> Results</B></P><P> Twenty-eight trials involving 2174 patients met the inclusion criteria. Although there were some exceptions, the methodological quality was typically low. Seventeen trials reported the incidence rate of CIPN assessed by various tools and 14 showed a significant difference regarding the decrease of the incidence rate between the two groups. For clinical improvement, 12 trials reported it using various tools and 10 showed a significant difference between two groups. Two cases of adverse events occurred in one trial; the other nine trials reported no adverse events.</P><P><B> Conclusions</B></P><P> We found that herbal medicines in combination with and/or without other therapies potentially have preventive or therapeutic effects on CIPN. However, conclusions cannot be drawn because of the generally low quality of the methodology, the clinical heterogeneity, and the small sample size for each single herbal medicine. Trials that are more rigorous and report sufficient methodological data are needed.</P>