• Applied Science and Convergence Technology
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• v.23 no.5
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• pp.211-220
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• 2014

In this paper, we present a review of optical and structural studies of $GaBi_xAs_{1-x}$ epilayers grown by Molecular Beam Epitaxy (MBE) on (311)B and (001) GaAs substrates with different As fluxes. The results indicate that under near-stoichiometric conditions the bismuth incorporation is higher for samples grown on (311)B GaAs substrates than for those grown on (001) GaAs. In addition, carrier localization effects in GaBiAs layers are clearly revealed for both samples by optical measurements. The (311)B samples showed evidence of higher density of defects. It has also been found that the nonradiative centers play a significant role in the recombination process in this material system. The influence of post-growth annealing on the microstructural, optical, and magneto-optical properties was also investigated. An important improvement of optical and spin properties after thermal annealing due to the reduction of defects in the GaBiAs layers was observed.

• 전기의세계
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• v.28 no.4
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• pp.53-63
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• 1979

Interface recombination velocity in $Al_{x}$G $a_{1-x}$ As-GaAs and $Al_{0.85}$, G $a_{0.15}$ As-GaA $s_{1-y}$S $b_{y}$ heterojunction systems is studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n $Al_{x}$G $a_{1-x}$ As-GaA $s_{1-y}$S $b_{y}$-A $l_{x}$G $a_{1-x}$ As double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAs Sb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates. In the AlGaAs system, elastic lattice deformation with effective Poisson ratios .mu.$_{eff}$ (100=0.312 and .mu.$_{eff}$ (111B) =0.190 was observed. The lattice constant $a_{0}$ (A $l_{x}$G $a_{1-x}$ As)=5.6532+0.0084x.angs. was obtained at 300K which is in good Agreement with Vegard's law. In the GaAsSb system, although elastic lattice deformation was observed in (111) B-oriented crystals, misfit dislocations reduced the Poisson ratio to zero in (100)-oriented samples. When $a_{0}$ (GaSb)=6.0959 .angs. was assumed at 300K, both (100) and (111)B oriented GaAsSb layers deviated only slightly from Vegard's law. Both (100) and (111)B zero-mismatch $Al_{0.85}$ G $a_{0.15}$As-GaA $s_{1-y}$S $b_{y}$ layers were grown from melts with a weight ratio of $W_{sb}$ / $W_{Ga}$ =0.13 and a growth temperature of 840 to 820 .deg.C. The corresponding Sb compositions were y=0.015 and 0.024 on (100) and (111)B orientations, respectively. This occurs because of a fortuitous in the Sb distribution coefficient with orientation. Interface recombination velocity was estimated from the dependence of the effective minority carrier lifetime on double-heterojunction spacing, using either optical phase-shift or electroluminescence timedecay techniques. The recombination velocity at a (100) interface was reduced from (2 to 3)*10$^{4}$ for y=0 to (6 to 7)*10$^{3}$ cm/sec for lattice-matched $Al_{0.85}$G $a_{0.15}$As-GaA $s_{0.985}$S $b_{0.015}$ Although this reduction is slightly less than that expected from the exponential relationship between interface recombination velocity and lattice mismatch as found in the AlGaAs-GaAs system, solar cells constructed from such a combination of materials should have an excellent spectral response to photons with energies over the full range from 1.4 to 2.6 eV. Similar measurements on a (111) B oriented lattice-matched heterojunction produced some-what larger interface recombination velocities.ities.ities.s.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.626-631
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• 2005

GaN-related compound semiconductors were grown on the corrugated interface substrate using a metalorganic chemical vapor deposition system to increase the optical power of white LEDs. The patterning of substrate for enhancing the extraction efficiency was processed using an inductively coupled plasma reactive ion etching system and the surface morphology of the etched sapphire wafer and that of the non-etched surface were investigated using an atomic force microscope. The structural and optical properties of GaN grown on the corrugated interface substrate were characterized by a high-resolution x-ray diffraction, transmission electron microscopy, atomic force microscope and photoluminescence. The roughness of the etched sapphire wafer was higher than that of the non-etched one. The surface of III-nitride films grown on the hemispherically patterned wafer showed the nano-sized pin-holes that were not grown partially. In this case, the leakage current of the LED chip at the reverse bias was abruptly increased. The reason is that the hemispherically patterned region doesn't have (0001) plane that is favor for GaN growth. The lateral growth of the GaN layer grown on (0001) plane located in between the patterns was enhanced by raising the growth temperature ana lowering the reactor pressure resulting in the smooth surface over the patterned region. The crystal quality of GaN on the patterned substrate was also similar with that of GaN on the conventional substrate and no defect was detected in the interface. The optical power of the LED on the patterned substrate was $14\%$ higher than that on the conventional substrate due to the increased extraction efficiency.

• Korean Journal of Crystallography
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• v.1 no.2
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• pp.99-104
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• 1990

The hetero-epitaxial growth of AmB v type onto-electronic material is attempted by means of the laser-induced chemical vapour deposition technique. The bimolecular gas phase reaction of trimethylgallium with ammonia on (001) alumina substrate for the epitaxy of gallium nitride is chosen as a model system. In this study, ArF exciter laser (193nm) is employed as a photon source. Marked difference is found in nucleation and in subsequent crystal incorporation between the doposits formed with and without the laser-irradiation. The surface coverage with isomorphically grown drystallites is pronounced upon "volume-excited" irradiation in comparison with the conventional thermal process. As to the crystal structure of the grown layers, the laser-induced deposits of GaN may be represented by either of the following two models: (001) plane of sapphire //y (001) plane of wurtzite-type GaN, OR (001) plane of sapphire//(001) plane of wurtzite-type-GaN (111) plane of twinned zinc blende-type GaN.

• Journal of Microbiology and Biotechnology
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• v.29 no.6
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• pp.973-983
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• 2019

It is well known that iron is critical for bacterial growth and pathogenic virulence. Due to chemical similarity, $Ga^{3+}$ competes with $Fe^{3+}$ for binding to compounds that usually bind $Fe^{3+}$, thereby interfering with various essential biological reactions. In our present study, gallium(III) nitrate [$Ga(NO_3)_3$] could repress the growth of V. splendidus Vs without complete inhibition. In the presence of $Ga(NO_3)_3$, the secretion of homogentisic acid-melanin (HGA-melanin) in V. splendidus Vs cells could be increased by 4.8-fold, compared to that in the absence of $Ga(NO_3)_3$. HGA-melanin possessed the ability to reduce $Fe^{3+}$ to $Fe^{2+}$. In addition, HGA-melanin increased the mRNA levels of feoA and feoB, genes coding Fe2+ transport system proteins to 1.86- and 6.1-fold, respectively, and promoted bacterial growth to 139.2%. Similarly, the mRNA expression of feoA and feoB was upregulated 4.11-fold and 2.71-fold in the presence of $640{\mu}M$ $Ga(NO_3)_3$, respectively. In conclusion, our study suggested that although $Ga(NO_3)_3$ could interfere with the growth of V. splendidus Vs, it could also stimulate both the production of $Fe^{3+}$-reducing HGA-melanin and the expression of feoA and feoB, which facilitate $Fe^{2+}$ transport in V. splendidus Vs.

• Korean Journal of Materials Research
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• v.22 no.4
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.51-51
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• 2010

Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.226-226
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• 2013

GaN는 III-V족 물질로 밴드갭이 3.4 eV으로 가시광선 영역에서 투명하며 우수한 전기적 특성으로 인해 여러 반도체 분야에서 응용되고 있는 물질이다. GaN 박막의 성장 방법으로는 molecular beam epitaxial 방법과 metal organic chemical vapor deposition 방법이 있지만 고비용인 단점이 있다. 이에 비해 sputtering 방법으로 성장시킨 GaN 박막은 비용이 적게 들고 저온에서 성장이 가능하다는 장점이 있다. 이 연구에서는 radio frequency sputter를 사용하여 GaN 박막을 성장하여 구조적, 광학적 특성을 분석하였다. GaN 박막은 각각 단일층의 그래핀과 c-축 사파이어 기판에 증착 하였으며, 이때 기판온도는 $25^{\circ}C$, $100^{\circ}C$, $200^{\circ}C$로 변화를 주었고, N2 분압은 2 sccm, 5 sccm, 10 sccm으로 변화를 주었다. 그래핀과 사파이어 기판에 성장된 각각의 GaN 박막의 결정성을 투과전자현미경 이미지로 측정하여 비교하였다. $4{\times}10^{-3}$ Torr 진공도와 50 W의 방전 전력과 Ar 10 sccm 분위기에서 20 min 동안 증착된 GaN 박막 두께는 70 nm정도를 가지는 것으로 확인하였다. X-ray Diffraction 측정으로 사파이어 기판 및 (002) 방향으로 성장된 GaN의 피크를 확인하였다. 추가적으로 Photoluminescence 스펙트럼은 N2 분압의 변화와 yellow luminescence 영향을 받는 것을 확인하였다. 본 연구를 통하여, 증착된 기판온도와 N2 분압의 변화에 따른 그래핀 및 사파이어 기판에 증착된 GaN 박막의 특성을 비교하였으며, sputtering 방법으로 고품질의 GaN 박막을 성장시킬 수 있는 가능성을 확인하였다.

• Journal of the Mineralogical Society of Korea
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• v.23 no.3
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• pp.267-272
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• 2010

High pressure x-ray diffraction patterns of ${\alpha}$-cristobalite gallium phosphate ($GaPO_4$) were acquired up to 8.9 GPa at room temperature using Mao-Bell type diamond anvil cell with high flux synchrotron radiation. Starting orthorhombic phase (phase-I) shows the splitting of peak which is possibly resulted from the pressure induced orientation disorder of the framework structure of tetrahedra. This is designated as phase-I'. This phase transforms to the orthorhombic high pressure phase-III between 2 and 3 GPa. Present phase transition sequence is not in accord with the recent high pressure X-ray diffraction results performed on the same starting sample (Ming et al., 2007). X-ray pattern of the unloaded sample to ambient pressure shows that the structure retains that of the high pressure phase prior to decompression.

• Health and Mission
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• s.23
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• pp.14-17
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• 2011