• 한국결정성장학회지
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• 제19권3호
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• pp.152-158
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• 2009

산업용 뿐만 아니라 보석용으로 가치가 있는 사파이어는 매우 다양한 방법으로 합성 사파이어를 만들어 왔다. 그 중 천연 사파이어와 매우 유사하며 보석용으로 가치가 높은 Chatham사의 플럭스 사파이어를 사용하여 천연 사파이어와 비교하였다. 먼저 WD-XRF(Wavelength dispersive x-ray fluorescence spectrometer)를 사용하여 천연과 합성의 화학 조성을 비교하였다. 천연 사파이어는 화학 조성이 매우 다양하였으나 플럭스 사파이어는 천연과 유사한 화학 성분과 특히 Mo, Pt, Pb 미량원소가 검출되었다. Pt는 플럭스 사파이어라는 결정적인 증거가 된다. 다음으로 $1300^{\circ}C$와 $1500^{\circ}C$의 고온에서 열처리를 한 후 자외선-가시광선 분광광도계(UV-VIS Spectrophotometer)를 사용하여 분광학적 특성을 조사함으로써 천연 사파이어는 $Cr^{3+}$와 관련된 약 690nm의 형광과 관련된 흡수 피크의 변화를 관찰할 수 있었고 플럭스 사파이어는 $Cr^{3+}$와 관련된 약 690nm의 피크와 376nm, 388nm의 $Fe^{3+}$의 흡수 피크가 변화함을 볼 수 있었다. 고온 열처리에 의해 플럭스 사파이어의 흡수 피크의 변화가 천연 사파이어의 흡수 피크의 변화보다 더 큰 것을 알 수 있었다 화학조성 및 분광분석 실험을 통하여 천연 사파이어와 flux 합성 사파이어의 특성을 비교 분석하였다.

• 한국세라믹학회지
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• 제25권2호
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• pp.95-100
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• 1988

Single crystals of sapphire were grown from solution by slow cooling method using B2O3 and PbO as flux agents. The morphology of grown crystals was tube, rhombohedral, or hexagonal-plate. It was found that the morphology and the size of grown crystal were highly dependent on the amount of fluxes in the solution, the ratio of B2O3 vs. PbO, and cooling rate.

• 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.

• 한국결정성장학회지
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• 제8권1호
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• pp.1-9
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• 1998

본 연구에서는 냉각매체로서 물을 이용하는 수정된 열교환법을 이용하여 45$\times$45$\times$20(mm) 크기의 사각단면 형상의 sapphire 단결정의 제조가능 조건에 대하여 조사하였다. 온도에 따른 성장로 내의 압력 변화로부터 사파이어의 용융 및 응고 과정을 추적할 수 있었으며, 이로부터 sapphire 단결정은 1970~$1960^{\circ}C$에서 응고가 완료됨을 알 수 있었다. 도가니 성형시 이루어지는 '귀'의 형태는 도가니 벽면과 접촉되지 않는 '나선형태'이어야 한다. 열유출부는 융액 내의 온도구배를 지배하며 융액내의 열유속과 씨앗 결정의 흔적은 Mo 봉의 체적 변화로서 조절할 수 있었다. 기공 형성을 억제하기 위해서는 $0.2^{\circ}C$/min 이하의 발열체의 냉각속도가 요구되었다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권3호
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• pp.199-205
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• 2006

Patterned sapphire substrates (PSS) were fabricated by a simple wet etching process with $SiO_2$ stripe masks and a mixed solution of $H_2SO_4$ and $H_3PO_4$. GaN layers were epitaxially grown on the PSS under the optimized 2-step growth condition of metalorganic vapor deposition. During the 1st growth step, GaN layers with triangular cross sections were grown on the selected area of the surface of the PSS, and in the 2nd growth step, the GaN layers were laterally grown and coalesced with neighboring GaN layers. The density of threading dislocations on the surface of the coalesced GaN layer was $2{\sim}4\;{\times}\;10^7\;cm^{-2}$ over the entire region. The epitaxial structure of near-UV light emitting diode (LED) was grown over the GaN layers on the PSS. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the PSS were remarkably increased when compared to the conventional LED structure grown on the flat sapphire substrate. The reduction in TD density and the decrease in the number of times of total internal reflections of the light flux are mainly attributed due to high level of scattering on the PSS.

• Progress in Superconductivity
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• 제5권2호
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• pp.94-97
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• 2004

Step-edge Josephson junctions (SEJ) have been fabricated on sapphire substrates with in situ deposited films of CeO$_2$ buffer layer and YBa$_2$Cu$_3$O$_{7}$ films on the low angle steps. Direct coupled SQUID magnetometers with the SEJ were formed on 1 cm X 1 cm R-plane sapphire substrates. Typical 5-${\mu}{\textrm}{m}$-wide Josephson junctions have R$_{N}$ of 3 Ω and I$_{c}$ of 50 $mutextrm{A}$ at 77 K. The direct coupled SQUID magnetometers were designed to have pickup coils of 50-${\mu}{\textrm}{m}$-wide 16 parallel loops on the 1 cm X 1 cm substrates with outer dimension of 8.8 mm X 8.8 mm. The SEJ SQUID magnetometers exhibit relatively low 1/f noise even with dc bias control, and could be stably controlled by flux-locked loops in the magnetically disturbed environment. Field noise of the do SQUID was measured to be 200∼300 fT/Hz$^{1}$2/in the white noise region and about 2 pT/Hz$^{1}$2/ at 1 Hz when measured with dc bias method.hod.d.

• 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.

• 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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.252-256
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• 2000

We investigated resistance development in Au/YBCO thin film meander lines during quench. The meander lines were fabricated by coating YBCO films insitu with a gold layer and patterning them by photolithography. The center stripe quenched fastest even though the flux flow resistance that appeared upon the current passing the critical current was uniform. Quench started at an area of the center stripe and propagate both through the gold layer and the sapphire substrate. Quench propagation speed was uniform and 60 cm/s at 30 V$_{rms}$.

• 열처리공학회지
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• 제31권5호
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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.