• 한국진공학회지
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• 제10권1호
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• pp.22-26
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• 2001

Plasma assisted molecular beam epitaxy(PAMBE)를 사용하여 Si 기판위에 성장시킨 AlN 박막에 대하여 성장온도 및 기판의 방향성에 따른 박막의 결정성 변화를 분석하였다. Reflection high energy electron diffraction(RHEED) 패턴을 이용하여 성장 중의 결정성을 관찰하였고, 성장 후에는 X-ray diffraction(XRD), double crystal X-ray diffraction(DCXD), transmission electron microscopy/diffraction(TEM/TED)분석을 하였다. $850^{\circ}C$이상의 온도에서 Si(100)위에 성장된 AlN박막은 육방정계의 c축 방향으로 우선 배향되어 있음을 확인하였으며 Si(111)위에 성장된 AlN박막의 경우 AlN(0001)/Si(111), AlN(1100)/Si(110), AlN(1120)/Si(112)의 결정방위를 가지고 성장하였음을 확인하였다. 또한 Si(111) 기판 위에서는 전위와 적층결함 등 많은 결정결함에 의해 DCD패턴의 반치폭이 2$\theta$=$36.2^{\circ}$에서 약 3000arcsec에 이르는 등 결정성은 좋지 않았으나 AlN박막이 단결정으로 성장된 것으로 나타났다.

• 한국재료학회지
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• 제19권5호
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• pp.281-287
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• 2009

ZnO thin film was grown on a sapphire single crystal substrate by plasma assisted molecular beam epitaxy. In addition to near band edge (NBE) emissions, both blue and green luminescences are also observed together. The PL intensity of the blue luminescence (BL) range from 2.7 to 2.9 eV increased as the amount of activated oxygen increased, but green luminescence (GL) was weakly observed at about 2.4 eV without much change in intensity. This result is quite unlike previous studies in which BL and GL were regarded as the transition between shallow donor levels such as oxygen vacancy and interstitial zinc. Based on the transition level and formation energy of the ZnO intrinsic defects predicted through the first principle calculation, which employs density functional approximation (DFA) revised by local density approximation (LDA) and the LDA+U approach, the green and blue luminescence are nearly coincident with the transition from the conduction band to zinc vacancies of $V^{2-}_{Zn}$ and $V^-_{Zn}$, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2004년도 제27회 학술발표회 초록집
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• pp.246-246
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• 2004

• 한국진공학회:학술대회논문집
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• 한국진공학회 2008년도 제35회 하계학술대회 초록집
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• pp.101-101
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• 2008

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.114-114
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• 2009

ZnO has received considerable attention due to its potential applicability to optoelectronic devices such as ultraviolet-light emitting diodes (UVLEDs) and laser diodes (LDs). As well known, however, polar ZnO with the growth direction along the c-axis has spontaneous and piezoelectric polarizations that will result in decreased quantum efficiency. Recently, nonpolar ZnO has been studied to avoid such a polarization effect. In order to realize applications of nonpoar ZnO-based films to LEDs, growth of high quality alloys for quantum well structures is one of the important tasks that should be solved. $Mg_xZn_{1-x}O$ and $Cd_xZn_{1-x}O$ is ones of most promising alloys for this application because the alloys of ZnO with MgO and CdO provide a wide range of band-gap engineering spanning from 2.4 to 7.8 eV. In this study, we investigated on $Mg_xZn_{1-x}O$ films grown with various Mg/Zn flux ratios The films were grown on R-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). we investigated on $Mg_xZn_{1-x}O$ films grown with various Mg/Zn flux ratios. The films were grown on R-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). With the relatively low Mg/Zn flux ratios, a typical striated anisotropic surface morphology which was generally observed from the nonpolar (11-20) ZnO film on r-plane sapphire substrates. By increasing the Mg/Zn flux ratio, however, additional islands were appeared on the surface and finally the surface morphology was entirely changed, which was generally observed for the (0001) polar ZnO films by losing the striated morphology. Investigations by X-ray $\Theta-2{\Theta}$ diffraction revealed that (0002) and (10-11) ZnO planes are appeared in $Mg_xZn_{1-x}O$ films by increasing the Mg/Zn flux ratio. Further detailed investigation by transmission electron microscopy (TEM) and photoluminescence (PL) will be discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.247-247
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• 2011

플라즈마 분자선 에피택시(plasma-assisted molecular beam epitaxy)법을 이용하여 다공질 실리콘(porous silicon)에 ZnO 박막을 성장하였다. 성장 후, 아르곤 분위기에서 10분 간 다양한 온도(500~700$^{\circ}C$)로 열처리하였다. 다공질 실리콘 및 열처리 온도가 ZnO 박막의 특성에 미치는 영향을 scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL)을 이용하여 분석하였다. 실리콘 기판에 성장된 ZnO 박막은 일반적은 섬구조(island structure)로 성장된 반면, 다공질 실리콘에 성장된 ZnO 박막은 산맥과 같은 구조(mountain range-like structure)로 성장되었다. 열처리 온도가 증가함에 따라 ZnO 박막의 grain size는 증가하였다. 실리콘 기판 위에 성장된 ZnO 박막은 wurtzite 구조를 나타내는 여러 개의 회절 피크가 관찰된 반면, 다공질 실리콘에 성장된 ZnO 박막은 c-축 배향성(c-axis preferred orientation)을 나타내는 ZnO (002) 회절 피크만이 나타났다. 다공질 실리콘에 성장된 ZnO 박막의 구조적 및 광학적 특성이 실리콘 기판에 성장된 ZnO 박막의 특성보다 우수하게 나타났다. 뿐만 아니라, 열처리 온도가 증가함에 따라 다공질 실리콘에 성장된 ZnO 박막의 PL 강도비(intensity ratio)가 실리콘 기판에 성장된 ZnO 박막의 강도비보다 월등하게 증가하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.155-156
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• 2006

Single crystalline ZnO fims were successfully grown on r-plane sapphire substrate by plasma-assisted molecular beam epitaxy. Epitaxial relationship between the ZnO film and the-r-plane sapphire was determined to be [-1101]$Al_2O_3\;{\parallel}$ [0001]ZnO, [11-20]$Al_2O_3\;{\parallel}$ [-1100]ZnO based on the in-situ RHEED analysis and confirmed again by HRXRD measurements. Grown (11-20) ZnO films showed faceted structure along the <0001> direction and the RMS roughness was about 4 nm.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.119-119
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• 2010

We report strong exciton transition and exciton-phonon couplings in photoluminescence (PL) of ZnO thin films grown on MgO/sapphire (buffer/substrate) by plasma-assisted molecular beam epitaxy. The PL spectra at 10 K showed the intensity of the dominant emission, donor-bound exciton transition of front surface (top surface, the latter part in growth) is found to be about 100 times higher than that of back surface (in-depth bottom area, the initial part), while the room temperature PL spectra showed dominant contributions from the free exciton emissions and phonon-replicas of free excitons for front surface and back surface, respectively, It could be attributed to the strong contributions of exciton-phonon coupling. Time resolved PL spectra reveal that the life time of exciton recombination from the front surface are longer than those from back surface. This is most probably due to the fact that reduction of non-radiative recombination in the front surface. This investigation indicates that the existence of native defects or trap centers which can be reduced by the proper initial condition in growth and the exciton-phonon interaction couplings play an important role in optical properties and crystal quality of ZnO thin films.

• 한국재료학회지
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• 제22권4호
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• pp.185-189
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• 2012

We report plasma-assisted molecular beam epitaxy of $In_XGa_{1-X}N$ films on c-plane sapphire substrates. Prior to the growth of $In_XGa_{1-X}N$ films, GaN film was grown on the nitride c-plane sapphire substrate by two-dimensional (2D) growth mode. For the growth of GaN, Ga flux of $3.7{\times}10^{-8}$ torr as a beam equivalent pressure (BEP) and a plasma power of 150 W with a nitrogen flow rate of 0.76 sccm were fixed. The growth of 2D GaN growth was confirmed by $in-situ$ reflection high-energy electron diffraction (RHEED) by observing a streaky RHEED pattern with a strong specular spot. InN films showed lower growth rates even with the same growth conditions (same growth temperature, same plasma condition, and same BEP value of III element) than those of GaN films. It was observed that the growth rate of GaN is 1.7 times higher than that of InN, which is probably caused by the higher vapor pressure of In. For the growth of $In_xGa_{1-x}N$ films with different In compositions, total III-element flux (Ga plus In BEPs) was set to $3.7{\times}10^{-8}$ torr, which was the BEP value for the 2D growth of GaN. The In compositions of the $In_xGa_{1-x}N$ films were determined to be 28, 41, 45, and 53% based on the peak position of (0002) reflection in x-ray ${\theta}-2{\theta}$ measurements. The growth of $In_xGa_{1-x}N$ films did not show a streaky RHEED pattern but showed spotty patterns with weak streaky lines. This means that the net sticking coefficients of In and Ga, considered based on the growth rates of GaN and InN, are not the only factor governing the growth mode; another factor such as migration velocity should be considered. The sample with an In composition of 41% showed the lowest full width at half maximum value of 0.20 degree from the x-ray (0002) omega rocking curve measurements and the lowest root mean square roughness value of 0.71 nm.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.95-96
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• 2005

The general method and mechanism for the polarity control of heteroepitaxial wurtzite films, such as ZnO and GaN, by interface engineering via plasma-assisted molecular beam epitaxy are addressed. We proposed the principle and method controlling the crystal polarity of ZnO on GaN and GaN on ZnO. The crystal polarity of the lower film was maintained by forming a heterointerfce without any interface layer between the upper and the lower layers. However the crystal polarity could be changed by forming the heterointerface with the interface layer having an inversion center. The principle and method suggested here give us a promising tool to fabricate polarity inverted heterostructures, which applicable to invent novel heterostructures and devices.