• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.485-485
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• 2013

Plasma-assisted molecular beam epitaxy법으로 자가 형성되는 InN 박막을 활용하여 GaN 박막의 결함밀도를 감소시키는 성장 구조 조건에 대하여 연구하였다. Sapphire 기판 위에 저온에서 GaN 핵층을 3 nm 두께로 성장하고, 그 위에 InN 박막을 성장 한 후, 고온에서 GaN을 성장하였다. InN박막의 성장 온도는 $450^{\circ}C$이고, 성장 시간을 30초에서 1분 30초까지 각각 달리 하였다. 실험결과 InN 층이 삽입된 GaN 박막이 상대적으로 고른 표면이 형성되는 과정을 reflection high energy electron diffraction로 관측하였고, atomic force microscope를 측정하여 표면 거칠기의 개선을 확인하였다. InN 성장시간 변화에 따른 결정학적, 광학적 특성 변화를 x-ray diffraction, photoluminescence 이용하여 조사하였고, 본 연구를 통해 InN박막을 활용한 양질의 GaN 박막 성장 가능성을 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.161-162
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• 2007

(1-102) R-면 사파이어 기판 위에 플라즈마 분자선 에피탁시 법으로 성장시킨 비극성 ZnO 박막의 표면 형상을 원자력간현미경(AFM) 및 투과전자현미경으로 분석하였다. AFM 관찰 결과 ZnO<0001> 방향으로 길쭉한 제방 모양의 표면 형상이 나타남을 알 수 있었고, 고분해능 투과전자현미경 관찰을 통해 박막 성장 중에 관찰되는 V(chevron 모양) 형상의 in-situ RHEED 패턴을 야기시키는 박막 표면의 facet 면을 원자 level에서 확인하였다.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.3
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• pp.124-131
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• 2016

GaN and InN epilayers with nucleation layer (LT-buffer) were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). As-grown and annealed GaN and InN nucleation layers grown at various growth condition were observed by reflection high-energy electron diffraction (RHEED). When temperature of effusion cell for III source was very low, diffraction pattern with cubic symmetry was observed and zincblende nucleation layer was flattened easily by annealing. As cell temperature increased, LT-GaN and LT-InN showed typical diffraction pattern from wurtzite structure, and FWHM of (10-12) plane decreased remarkably which means much improved crystalline quality. Diffraction pattern was changed to be from streaky to spotty when plasma power was raised from 160 to 220 W because higher plasma power makes more nitrogen adatoms on the surface and suppressed surface mobility of III species. Therefore, though wurtzite nucleation layer was a little hard to be flattened compared to zincblende, higher cell temperature led to easier movement of III surface adatoms and resulted in better crystalline quality of GaN and InN epilayers.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.298-304
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• 2007

We have studied the effect of $N_2$ flow rate on the structural and optical properties of GaN nanorods grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy. The hexagonal shape nanorods with lateral diameters from 80 to 190 nm with increasing $N_2$ flow rate from 1.1 to 2.0 sccm are obtained. However, the ratio of length (thickness) and compact region increases with increasing $N_2$ flow rate up to 1.7 sccm and then saturate. From the photoluminescence, free exciton transition is clearly observed for GaN nanorods with low $N_2$ flow rate. And the PL peak energies are blue-shifted with decreasing diameter of the GaN nanorods due to size effect. Temperature-dependent photoluminescence spectra for the nanorods with $N_2$ flow rate of 1.7 sccm show an abnormal behavior like "S-shape" with increasing temperature.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.5
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• pp.237-243
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• 2018

In-rich InGaN epilayers were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). InGaN epilayers grown at various growth condition were observed by SEM, XRD, and RHEED. When plasma power of nitrogen increased from 290 to 350 W, surface morphology and crystal quality became worse according to more active nitrogen on the surface of InGaN at N-rich growth condition. As In composition was reduced from 89 to 71% by changing the incoming flux of In and Ga, surface morphology and crystal quality became worse. In addition, weak peaks of cubic InGaN phase was observed from InGaN layer with 71% In composition by XRD ${\Phi}$ scan measurement. When growth temperature decreased from 500 to $400^{\circ}C$, RHEED diffraction pattern was changed to be from streaky to spotty which means atomically rough surface, and spotty pattern showed cubic symmetry of InGaN clearly. XRD ${\Phi}$ scan measurement gave clear evidence that more cubic InGaN phase was formed at low growth temperature. All these results indicates that extremely low surface mobility of Ga adatom caused inferior crystal quality and cubic InGaN phase.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.161-164
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• 2001

Transmuted impurity atoms formed in neutron-irradiated ZnO thin films were theoretically identified first and then experimentally confirmed by Photoluminescence (PL). ZnO thin films grown by plasma-assisted molecular beam epitaxy were irradiated by neutron beam at room temperature. Among eight isotropes naturely exiting in ZnO films, only $^{64}Zn$, $^{68}Zn$, $^{70}Zn$ and $^{18}O$ were expected to transmute into $^{65}Cu$, $^{69}Ga$, $^{71}Ga$ and $^{19}F$, respectively. The concentrations of these transmuted atoms were estimated by considering natural abundance, neutron fluence, and neutron cross section. The neutron-irradiated ZnO thin films were characterized by PL. In the PL spectra of these ZnO thin film, the Cu-related PL peaks were seen, but the Ga- or F-associated PL peaks were absent. This observation demonstrates the existence of $^{65}Cu$ in the ZnO. In this paper, emission mechanism of Cu impurities wil1 be described and the reason for the absence of the Ga- or F-associated PL peaks will be discussed.

• Applied Science and Convergence Technology
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• v.26 no.3
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• pp.52-54
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• 2017

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.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.7
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• pp.298-304
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• 2002

Transmuted impurity atoms formed in neutron-irradiated ZnO thin films were theoretically identified first and then experimentally confirmed by photoluminescence (PL). ZnO thin films grown by plasma-assisted molecular beam epitaxy were irradiated by neutron beam at room temperature. The ZnO films consist of eight constituent (Zn and O) isotropes, of which four are transmutable by neutron-irradiation; $^{64}$ , $^{68}$ Zn, $^{70}$ Zn and $^{18}$ O were expected to transmute into $^{65}$ Cu, $^{69}$ Ga, $^{71}$ Ga, and $^{19}$ F, respectively. The concentrations of these transmuted atoms were estimated in this study by considering natural abundance, neutron fluence and neutron cross section. The neutron-irradiated ZnO thin films were characterized by PL. In the PL spectra of the ZnO thin films, the Cu-related PL peaks were seen, but the Ga- or F-associated PL peaks were absent. This observation confirmed the existence of $^{65}$ Cu in the ZnO, but it could not do the formation of the other two. In this paper, the emission mechanism of Cu impurities is described and the reason for the absence of the Ga- or F-associated PL peaks is discussed as well.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.752-758
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• 2004

This paper reports on the DC and RF characteristics of AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beau epitaxy(MBE) on sapphire substrates. The devices with a 0.5 ${\mu}$m gate-length exhibited relatively flat transconductance(g$\_$m/), which results from the enhanced carrier confinement of the InGaN channel. The maximum drain current was 880 mA/mm with a peak g$\_$m/ of 156 mS/mm, an f$\_$T/ of 17.3 GHz, and an f$\_$MAX/ or 28.7 GHz. In addition to promising DC and RF results, pulsed I-V and current-switching measurements showed little dispersion in the unpassivated AlGaN/InGaN HEMTs. These results suggest that the addition of In to the GaN channel improves the electron transport characteristics as well as suppressing current collapse that is related to the surface trap states.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.240-248
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• 2002

$Fe_xTi_{l-x}O_2$ films (x=0.07 and 0.16) were grown by oxygen-plasma-assisted molecular beam epitaxy on rutile $TiO_2$(110). The same growth conditions were applied for both films in order to determine surface characteristics of grown films as a function of Fe composition. The films were characterized by several surface analysis techniques. The oxidation states of Ti and Fe in $Fe_xTi_{l-x}O_2$ films were found to be +4 and a mixture of +2 and +3, respectively. More $Fe^{3+}$ species exist in higher Fe doped film of $Fe_{0.16}Ti_{0.84}O_2$. The morphology of $Fe_{0.07}Ti_{0.93}O_2$ film shows tall rectangular and cylinderical islands growth on flat substrate-like surface. On the other hand, $Fe_{0.16}Ti_{0.84}O_2$ film consists of round shaped small islands showing somewhat rougher surface compared to the surface of $Fe_{0.16}Ti_{0.84}O_2$ film.