• Korean Journal of Pharmacognosy
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• v.17 no.2
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• pp.178-183
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• 1986

It was our working hypothesis that introduction of 11-keto groups to 12-oleanene/ursene series of triterpenoids should endow them with corticoid-like activities, since pharmacological actions of glycyrrhetinic acid (GA) are known to be caused by inhibition on $corticoid-{\delta}^4-reductase$. 11-Keto-triterpenoids derived artificially in these studies, such as 11, 19-diketo-18, 19-secoursolic acid methyl ester(I), $11-keto-{\beta}-boswellic$ acid derivatives (IIa-IIc), 11-Keto-presenegenin dimethyl ester (III), II-keto-oleanolic acid derivatives (IVa-IVd) and 11-keto-hederagenin (V) possess the fundamental functions of ${\alpha},\;{\beta}-unsaturated$ ketone on C-11 and hydroxyl group on C-3, as like GA (VI). Additionally, they involve the carboxyl groups on rings A (II, III), D (I, III, IV, V) and E (VI), and the hydroxyl groups on rings A (III, V) and C (III). All the compounds competitively inhibited $corticoid-5{\beta}-reductase$, and the highest inhibitory potency appeared in I. All of them except $3,\;11-diketo-{\beta}-boswellic$ acid methyl ester (IIc) were more effective about five times to twice than GA. On carrageenin-induced edema test, compounds I and IVa-IVd showed anti-inflammatory activities, but III enhanced rather edema. Structure-activity relations were found in the aspects of hydrophilicity of ring A and hydrophobicity of rings C/D. The more they were hydrophilic in ring A and hydrophobic in rings C/D, the more they inhibited the enzyme. And the more they were hydrophobic in rings C/D, the more they exhibited antiiflammatory activities. However, the increased hydrophilicity in ring A resulted in increasing edema, probably due to a nonspecific inhibition on $aldosterone-5{\beta}-reductase$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.4
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• pp.157-161
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• 2006

InGaN layers on GaN templated sapphire (0001) substrates were grown by mixed-source hydride vapor phase epitaxy (HVPE) method. In order to get InGaN layers, Ga-mixed In metal and $NH_3$ gas were used as group III and group V source materials, respectively. The InGaN material was compounded from chemical reaction between $NH_3$ and indium-gallium chloride farmed by HCl flowed over metallic In mixed with Ga. The grown layers were confirmed to be InGaN ternary crystal alloys by X-ray photoelectron spectroscopy (XPS). In concentration of the InGaN layers grown by selective area growth (SAG) method was investigated by the photoluminescence (PL) and cathodoluminescence (CL) measurements. Indium concentration was estimated to be in the range 3 %. Moreover, as a new attempt in obtaining InAlGaN layers, the growth of the thick InAlGaN layers was performed by putting small amount of Ga and Al into the In source. We found the new results that the metallic In mixed with Ga (and Al) as a group III source material could be used in the growth process of the In(Al)GaN layers by the mixed-source HVPE method.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.133-133
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• 2010

3-5족 화합물 반도체를 이용한 집광형 삼중 접합 태양전지는 35% 이상의 광변환 효율로 주목을 받고 있다. 일반적으로 삼중 접합 태양전지는 넓은 영역대의 파장을 흡수하기 위해 밴드갭이 다른 InGaP, GaAs, Ge이 사용된다. 그 중 하부셀은 기계적 강도가 높고 장파장을 흡수할 수 있는 Ge이 사용되는데, p-type Ge 기판위에 III-V 결정막 성장 시 5족 원소가 확산되어 pn접합을 형성하게 된다. 이러한 구조를 가진 Ge 하부셀이 효율적으로 홀-전자 쌍을 형성하기 위해서는 두꺼운 베이스와 얇은 에미터 접합이 필요하다. InGaP의 phosphorus는 낮은 확산계수로 인해 GaAs의 arsenic에 비해 얇은 접합이 형성 가능하며, Ge표면 에칭효과가 더 적다는 장점이 있다. 이를 고려해 우리 연구그룹에서는 metalorganic chemical vapor depostion(MOCVD)을 이용하여 Ge기판위에 성장한 InGaP layer의 특성을 관찰해 보았다. <111>로 $6^{\circ}$ 기울어진 p-type Ge(100) 기판위에 MOCVD를 통해 InGaP layer를 형성하였고, 성장된 layer를 atomic force microscope(AFM)와 high-resolution x-ray diffraction(HRXRD)을 이용하여 표면형상, 조성, 응력상태 등을 각각 관찰하였다. 또한 phosphorus 확산에 의해 형성되는 도핑농도는 electrochemical capacitance-voltage(ECV)을 이용하여 관찰하였다. 성장된 Ge기판위의 InGaP layer의 경우 특징적으로 높이 50 nm, 밑변 길이 $1\;{\mu}m$의 경사진 표면을 관찰할 수 있었으며, 이러한 구조는 TMIn과 TMGa의 비율이 증가 할수록 감소하였다. 따라서 이러한 경사진 형태의 구조는 격자 불일치 때문인 것으로 판단된다. 추가적으로 V/III ratio의 최적화를 통해 1.3 nm의 표면 거칠기를 갖는 InGaP layer를 얻을 수 있었다. ECV를 통해 Ge 하부셀의 pn접합 형성을 관찰한 결과 약 160 nm에서 접합이 형성되는 것을 관찰할 수 있었다. 또한, 같은 성장 조건의 샘플을 1000 초 열처리 후에 접합깊이의 변화를 관찰한 결과 180 nm에서 접합이 관찰되었지만, GaAs의 arsenic에 의한 pn접합은 열처리 후에 그 깊이가 170 nm에서 300 nm로 증가 하였다. 따라서 삼중접합 태양전지의 제작 공정을 고려할 경우 phosphorus에 의한 접합 형성이 Ge 하부셀의 동작 특성에 유리할 것으로 판단된다.

• Solar Energy
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• v.18 no.3
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• pp.137-146
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• 1998

In this paper, the current status of manufacturing technologies for GaAs/Si solar cell were revived and provied new MOCVD. In the manufacturing process of GaAs/Si solar cells and an experiment to get the high efficiency GaAs solar cells, we must investigate the optimum growth conditions to get high quality GaAs films on Si substrates by MOCVD. The GaAs on Si substrates has been recognized as a lightweight alternative to pure substrate for space applicaton. Because its density is less the half of GaAs or Ge.So GaAs/Si has twofold weight advantage to GaAs monolithic cell. The theoretical conversion efficiecy limit of tandem GaAs/Si solar cell is 32% under AM 0 and $25^{\circ}C$ condition. It was concluded that the development of cost effective MOCVD technologies shoud be ahead GaAs solar cells for achived move high efficiency III-V solar cells involving tandem structure.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.387-395
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• 1999

The strain, surface and interfacial energies of III-V ternary systems were calculated for three kinds of structure modes: the Frank-van der Merwe(FM) mode, the Stanski-Krastanov(SK) mode and the Volmer-Weber(VW) mode. The free energy for each mode was estimated as functions of thickness and composition or lattice misfit. Through comparison of the free energy of each mode, it was found that the thickness-composition phase diagrams of III-V ternary systems can be determined only by considering the balance of the free energy and three kinds of structure modes appear in the phase diagrams. The SK mode appears only when the lattice misfit is large and/or the lattice layer is thick. The most stable structure of the SK mode is a cluster with four lattice layers or minimum thickness on a wetting layer of increasing lattice layers. The VW mode appears when the lattice misfit is large and the lattice layer is thin and only in the INPSb/InP and GaPSb/GaP system which have the largest lattice misfit of III-V ternary systems. The stable region of the SK mode in the GaPSb/GaP and InPSb/InP phase diagrams is largest of all because the composition dependence of the strain energy of these systems is stronger than that of the other systems. The critical number of lattice layers below which two-dimensional(2D) layers precede the three-dimensional(3D) nucleation in the SK mode at x=1.0 depends on the lattice misfit.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.354-358
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• 1997

Crystal properties of wurtzite GaN films grown on $Al_2O_3$(0001) substrates under various nitrogen pressure and plasma power by electron cyclotron resonance molecular beam epitaxy were investigated by full width at half maximum of X-ray diffraction peak and scanning electron microscope. It was found that the nitrogen pressure has a large effect on the FWHM value of XRD, and the GaN film grown under the optimum nitrogen pressure contains high density of dislocations. These results suggest that the crystal quality is sensitive to the plasma source conditions and that the relaxation of stress depends of V/III ratio. However, substrate-surface nitridation has little effect on the relaxation of misfit stress.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1274-1276
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• 1993

The silicon-nitride films formed by laser CVD method are used for passivating GaAs surfaces. The electrical Properties of metal-insulator-GaAs structure are studied to determined the interfacial characteristics by C-V curves and deep level transient spectroscopy(DLTS). The SiN films are photolysisly deposited from $SiH_4\;and\;NH_3$ in the range of $100^{\circ}C-300^{\circ}C$ on P type, (100) GaAs. The hysteresis is reduced and interface trap density is lowered to $10^{12}-10^{13}$ at $100^{\circ}C-200^{\circ}C$. The surface leakage current is studied too. The passivated GaAs have a little leakage current compared to non passivated GaAs.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.109-112
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• 2005

Cu계$I-III-VI_2$화합물은 직접천이형 반도체로 광흡수계수가 매우 높아 박막형 태양전지 제조에 매우 유리하다 또한 화학적으로 안정하며 Ga, A1등을 첨가하면 에너지 금지대폭을 조절할 수 있어 Wide Bandgap 태양전지 및 탠덤구조 태양전지를 제조하기에도 용이하다. $CuInSe_2(CIS)$ 물질에서 In을 $20-30\%$ 정도 치환한 $Cu(In,\;Ga)Se_2(CIGS)$ 태양전지의 경우 $19.5\%$의 세계 최고 효율을 보고하고 있으며 이는 다결정 실리콘 태양전지의 효율과 비슷한 수준이다. 본 연구에서는 동시 진공증발법을 이용하여 증착한 CIGS 박막 및 $CuGaSe_2(CGS)$ 박막을 이용하여 태양전지를 제조하였다. 공정의 재현성 및 결정립계가 큰 광흡수층 제조를 위하여 실시간 기판 온도 모니터링 시스템을 도입하였으며 버퍼층으로는 용액성장한 CdS 박막을 사용하였다. SLG/MO/CIGS(CGS)/CdS/ZnO/Al구조의 태양전지를 제조하여 면적 $0.5cm^2$에서 각각 $15\%$(CIGS)와 $7\%(CGS)$의 효율을 얻었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.6
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• pp.446-450
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• 2013

Growth mechanism of GS-MBE(Gas source-Molecular Beam Epitaxy) has been investigated. We observed that the growth rate of GaN films is changing from 520 nm/h to 440 nm/h by the variation of V/III ratio under nitrogen-rich growth condition. It was explained that the amount of hydrogen on the growth front varies by the ammonia flow, and gallium hydrides are generated on the surface by a reaction of hydrogen and gallium, resultantly the amount of gallium supplying is changing along with the $NH_3$ flow. Reflection high energy electron diffraction (RHEED) observation was used to confirm the N-rich condition. The crystal quality of GaN was estimated by photoluminescence (PL) and X-ray diffraction (XRD).

• Applied Science and Convergence Technology
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• v.26 no.4
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• pp.86-90
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• 2017

We have reported structural and optical properties of self-assembled InAs/GaAs quantum dot (QD) grown by molecular beam epitaxy with different arsenic to indium flux ratios (V/III ratios). By increasing the V/III ratio from 9 to 160, average diameter and height of the InAs QDs decreased, but areal density of them increased. The InAs QDs grown under V/III ratio of 30 had a highest-aspect-ratio of 0.134 among them grown with other conditions. Optical property of the InAs QD was investigated by the temperature-dependent photoluminescence (PL) and integrated PL. From the temperature dependence PL measurements of InAs QDs, the activation energies of $E_{a1}$ and $E_{a2}$ for the InAs QDs were obtained $48{\pm}3meV$ and $229{\pm}23meV$, respectively. It was considered that the values of $E_{a1}$ and $E_{a2}$ are corresponded to the energy difference between ground-state and first excited state, and the energy difference between ground-state and wetting layer, respectively.