• 한국진공학회지
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• 제19권5호
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• pp.365-370
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• 2010

분자선 에피택시 방법을 이용하여 GaAs 기판 위에 GaAs 및 AlGaAs 에피층을 성장하면서 성장 멈춤 효과를 연구하였다. 성장 멈춤 시간에 따른 에피층 성장 과정은 반사 고에너지 전자회절로 측정하였다. 성장 멈춤 시간은 0, 15, 30, 60초로 하였다. 그리고 성장 멈춤 시간을 달리하여 GaAs/$Al_{0.3}Ga_{0.7}As$ 다양자우물을 성장한 후 양자우물의 특성을 조사하였다. 반사 고에너지 전자회절의 강도 진동은 성장 멈춤 시간에 영향을 받고 있었다. 그리고 양자우물의 광특성도 성장 멈춤 시간에 의존하고 있었다. 성장 멈춤 시간이 30초일 때 우물과 장벽층 사이에 급준한 계면을 가지는 에피층을 얻을 수 있었다.

• 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.

• 한국재료학회지
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• 제24권5호
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• pp.266-270
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• 2014

Aluminum nitride(AlN) films were grown on the C-face and on the Si-face of (0001) silicon carbide(SiC) substrates using plasma-assisted molecular-beam epitaxy(PA-MBE). This study was focused on first-stage growth manipulation prior to the start of AlN growth. Al pre-exposure, N-plasma pre-exposure, and simultaneous exposure(Al and N-plasma) procedures were used in the investigation. In addition, substrate polarity and, first-stage growth manipulation strongly affected the growth and properties of the AlN films. Al pre-exposure on the C-face and on the Si-face of SiC substrates prior to initiation of the AlN growth resulted in the formation of hexagonal hillocks on the surface. However, crack formation was observed on the C-face of SiC substrates without Al pre-exposure. X-ray rocking-curve measurements revealed that the AlN epilayers grown on the Si-face of the SiC showed relatively lower tilt and twist mosaic than did the epilayers grown on the C-face of the SiC. The results from the investigations reported in this paper indicate that the growth conditions on the Si-face of the SiC without Al pre-exposure was highly preferred to obtain the overall high-quality AlN epilayers formed using PA-MBE.

• 한국재료학회지
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• 제29권9호
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• pp.542-546
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• 2019

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : $n^+-i(QD)-n^+$ QDIP with undoped quantum dot(QD) active region and $n^+-n^-(QD)-n^+$ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the $n^+-n^-(QD)-n^+$ structure, Si dopant is directly doped in InAs QD at $2{\times}10^{17}/cm^3$. Undoped and doped QDIPs show a photoresponse peak at about $8.3{\mu}m$, ranging from $6{\sim}10{\mu}m$ at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

• 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.

• 한국자기학회지
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• 제21권3호
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• pp.93-98
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• 2011

Laser Molecular-Beam Epitaxy 방법을 사용하여 $La_{0.35}Pr_{0.35}Ca_{0.3}MnO_3$(LPCMO)/$LaAlO_3$(LAO) 초격자를 성공적으로 증착하였으며 이의 열처리 전후 결정학적, 자기적 특성을 LPCMO 단층박막, 그리고 LPCMO/$SrTiO_3$(STO) 초격자와 비교 분석하였다. LPCMO 단층박막, 그리고 LPCMO/STO 초격자 단층박막의 경우, 표면이 열처리 전후 모두 거친 양상을 보인 것과는 달리 LPCMO/LAO 초격자 박막은 열처리 전후 모두 상대적으로 매우 매끈하였다. 열처리 후 단층박막, 초격자 박막 시료 모두 강자성 특성이 향상되었으며 특히 초격자의 경우에는 이러한 현상이 두드러졌다. 열처리 후에 보자력과 포화자기장이 감소하는 LPCMO 단층박막과는 달리 LPCMO/LAO 초격자의 경우, 열처리 후에도 보자력은 열처리 전과 같은 값을 보였으며 단층박막과는 반대로 포화자기장은 오히려 증가하였다. 이러한 자기적 특성은 절연체 사이에 강자성체가 끼여 있는 초격자라는 결정구조에서 기인하는 것으로 이해된다.

• Transactions on Electrical and Electronic Materials
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• 제1권3호
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• pp.18-22
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• 2000

In this work, we reported the sulfur compositional variation of ZnS$\_$x/Se$\_$1-x/ epitaxial layers with growth temperature and BEP ration of ZnX/Se/)P$\_$ZnS//P$\_$Se/) grown on GaAs substrates by molecular beam epitaxy. The sulfur composition of ZnSSe epitaxial layers was varied sensitively on the growth temperature and show different linear relationship with growth temperature and BEP ration of ZnS/Se(P$\_$ZnS//P$\_$Se/), which revealed -0.107 %$\^{C}$ at (P$\_$ZnS//P$\_$Se/)=0.30 and -0.052 %$\^{C}$ at (P$\_$ZnS//P$\_$Se/)=0.158 rspectively. A reference data for the accurate control of the sulfur composition and the growth of high quality ZnSSe/GaAs epitaxial layers was provided.

• 한국진공학회지
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• 제19권5호
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• pp.371-376
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• 2010

분자선 에피택시 장비를 이용하여 두 단계 방법(two-step method)으로 Si (100) 기판 위에 GaAs 에피층을 성장하였다. Si 기판은 초고진공을 유지하고 있는 MBE 성장 챔버 속에서 세척 방법을 달리하여 Si 기판표면에 존재하는 불순물(산소, 탄소 등)을 제거하였다. 첫 번째는 Si 기판을 몰리브덴 히터를 사용하여 $800^{\circ}C$로 직접 가열하였다. 두 번째는 Si 기판 표면에 As 빔을 조사시켜 주면서 $800^{\circ}C$로 Si 기판을 가열하였다. 세 번째는 Si 기판 표면에 Ga을 증착한 후 Si 기판을 $800^{\circ}C$로 가열하였다. 이와 같은 세 가지 다른 조건으로 세척한 Si(100) 기판 위에 성장한 GaAs 에피층의 특성은 reflection high-energy electron diffraction (RHEED), atomic force microscope (AFM), double crystal x-ray diffraction (DXRD), photoluminescence (PL), photoreflectance(PR) 등으로 조사하였다. Ga 빔을 증착하여 세척한 Si 기판 위에 성장된 GaAs 에피층의 RHEED 패턴은 ($2{\times}4$) 구조를 가지고 있었다. Ga 빔을 증착하여 세척한 Si 기판 위에 성장된 GaAs 에피층이 가장 좋은 결정성을 가지고 있었다.

• 한국재료학회지
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• 제21권11호
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• pp.634-638
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• 2011

We report growth of epitaxial AlN thin films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. To achieve two-dimensional growth the substrates were nitrided by nitrogen plasma prior to the AlN growth, which resulted in the formation of a two-dimensional single crystalline AlN layer. The formation of the two-dimensional AlN layer by the nitridation process was confirmed by the observation of streaky reflection high energy electron diffraction (RHEED) patterns. The growth of AlN thin films was performed on the nitrided AlN layer by changing the Al beam flux with the fixed nitrogen flux at 860$^{\circ}C$. The growth mode of AlN films was also affected by the beam flux. By increasing the Al beam flux, two-dimensional growth of AlN films was favored, and a very flat surface with a root mean square roughness of 0.196 nm (for the 2 ${\mu}m$ ${\times}$ 2 ${\mu}m$ area) was obtained. Interestingly, additional diffraction lines were observed for the two-dimensionally grown AlN films, which were probably caused by the Al adlayer, which was similar to a report of Ga adlayer in the two-dimensional growth of GaN. Al droplets were observed in the sample grown with a higher Al beam flux after cooling to room temperature, which resulted from the excessive Al flux.

• Applied Microscopy
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• 제36권spc1호
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• pp.35-40
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• 2006

Self-assembled InAs/GaAs quantum dots (QDs) were grown by the atomic layer epitaxy (ALE) and molecular beam epitaxy (MBE) techniques, The structure and the thermal stability of QDs have been studied by high resolution electron microscopy with in-situ heating experiment capability, The ALE and MBE QDs were found to form a hemispherical structure with side facets in the early stage of growth, Upon capping by GaAs layer, however, the apex of QDs changed to a flat one. The ALE QDs have larger size and more regular shape than those of MBE QDs. The QDs collapse due to elevated temperature was observed directly in atomic scale, In situ heating experiment within TEM revealed that the uncapped QDs remained stable up to $580^{\circ}C$, However, at temperature above $600^{\circ}C$, the QDs collapsed due to the diffusion and evaporation of In and As from the QDs, The density of the QDs decreased abruptly by this collapse and most of them disappeared at above $600^{\circ}C$.