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Wide band-gap반도체의 물성 및 고주파용 전력소자의 응용
신무환 한국전기전자재료학회 1996 電氣電子材料學會誌 Vol.9 No.9
본고에서는 여러가지 Wide Band-gap중에서 특히 최근에 많은 관심을 끌고 있는 GaN와 4H-SiC, 6H0SiC의 전자기적 물성을 소개하고 현재 이들로부터 제작된 prototype소자들의 성능을 비교함으로써 그 발전현황을 알아보기로 한다. 본고에서 관심을 두는 소자분야는 광전소자(optoelectronic devices)라기보다는 고주파 고출력용 전력소자임을 밝힌다. 아울러 GaN로부터 제작된 MESFET(MEtal Semiconductor Field-Effect Transistor)소자의 고주파 대역에서의 Large-Signal특성을 Device/Circuit Model을 통하여 실험치와 비교하여보고 이로부터 최적화된 channel 구조를 갖는 소자구조에서의 RF특성을 조사한다.
PLD 방법에 의해서 증착된 ZnO 박막의 전기적 특성 및 접합 특성에 관한 연구
강수창,신무환 한국전기전자재료학회 2002 전기전자재료학회논문지 Vol.15 No.1
In this study, metal/ZnO contacts were thermally annealed at different temperatures (as-dep., 400$^{\circ}C$, 600$^{\circ}C$, 800$^{\circ}C$, 1000$^{\circ}C$) for the investigation of electrical properties, and surface and interface characteristics. The analysis of the element composition and the chemical bonding state of the surface was made by the XPS(X-ray photoelectron spectroscopy). An attempt was made to establish the electrical property-microstructure relationship for the (Ti, Au)/ZnO. The Ti/ZnO contact exhibits an ohmic characteristics with a relatively high contact resistance of 4.74${\times}$10$\^$-1/ $\Omega$$\textrm{cm}^2$ after an annealing at 400$^{\circ}C$. The contact showed a schottky characteristics when the samples were annealed at higher temperature than 400$^{\circ}C$. The transition from the ohmic to schottky characteristics was contributed from the formation of the oxide layers as was confirmed by the peaks for O-O and Ti-O bondings in XPS analysis. For the Au/ZnO contact the lowest contact resistance was obtained from the as-deposited sample. The resistance was slowly increased with annealing temperature up to 600$^{\circ}C$. The ohmic characteristics were maintained eden fort 600$^{\circ}C$ annealing. The XPS analysis showed that the Au-O intensity was dramatically decreased with temperature above 600$^{\circ}C$.
CVPE(Chloride Vapor Phase Epitaxy)법에 의한 GaN 후막 증착과 열역학적 해석
박범진,신무환 명지대학교 대학원 1998 대학원논문집 Vol.2 No.-
This paper reports on a thermodynamic analysis for the GaN thick film growth by vapor phase epitaxy method. The thermodynamic calculation was performed using a chemical stoichiometric algorism. The simulation variables include the growth temperature in a range 400 - 1500 K, the gas ratios (GaCl_3)/(GaCl_3+NH_3) and (N_2)/(GaCl_3 + NH_3 ). The theoretical calculation predicts that the growth temperature of GaN be in the lower range of 450 - 750 K than the experimental results. The difference in the growth temperature between the simulation and the experiments indicates that the vapor phase epitaxy of GaN is kinetically limited, presumably, due to the high activation of the thin film growth.
이성분계 탄성 및 점탄성 재료의 내부응력이 확산에 미치는 영향
정삼원,신무환 명지대학교 산업기술연구소 2001 産業技術硏究所論文集 Vol.20 No.-
Free strain produced by diffusion occur from the difference in either i)the partial molar volumes or ii)the self-difusion coefficients between the components. In this paper the free strain from the difference in partial molar volumes were treated. It was assumed that stress was produced by diffusion withot making a new phase. All mechnical properties like Young's modulus, Poisson's ration and viscosity were assumed constant and isotropic. The mixture was assumed to follow elastic and viscoelastic behavior. With this assumptions, the differntial equations for concentration in elastic and Maxwell mixtures were obtained. The concentration change by diffusion as a function of time and position was obtained. The stress was also calculate from the concentration change as a function of time and position. The initial concnetration discontinuity at the interface was decreased with the relaxation of the induced stress in viscoelastic mixture but did not disappeared in elastic mixture.
박범진,박진호,신무환 한국결정성장학회 1998 한국결정성장학회지 Vol.8 No.3
본 연구에서는 기상화학 증착법으로 성장되는 GaN 후막에 대한 열역학적 전사모사를 수행하고 이를 실험결과와 비교, 검토하였다. 열역학적계산은 화학양론적 연산방식을 이용하여 수치 해석하였으며, 모사의 변수로써 온도범위는 400~1500K, 기상비율은 $(GaCl_3)/[GaCl_3+NH_3],(N_2)/(GaCl_3+NH_3)$를 취하였다. GaN의 성장온도 범위는 이론적인 계산이 실험결과보다 훨씬 낮은 450~750K으로 예측되었다. 성장온도에서 모사결과와 실험결과와의 차이는 GaN의 기상 에픽텍시 성장이 박막성장의 높은 활성화 에너지 때문에 반응속도론적으로 국한된 영역 내에서 발생한다는 것을 나타낸다. This paper reports on a thermodynamic analysis for the GaN thick film growth by vapor phase epitaxy method. The thermodynamic calculation was performed using a chemical stoichiometric algorism. The simulation variables include the growth temperature in a range 400~1500 K, the gas ratios $(GaCl_3)/(GaCl_3+NH_3)$ and $(N_2)/(GaCl_3+NH_3)$. The theoretical calculation predicts that the growth temperature of GaN be in the lower range of 450~750 K than the experimental results. The difference in the growth temperature between the simulation and the experiments indicates that the vapor phase epitaxy of GaN is kinetically limited, presumably, due to the high activation energy of thin film growth.
Raman 분광법에 의한 GaN OMVPE 전구체들의 열분해에 관한 연구
이순애,김유택,신무환,신건철,박진호 한국결정성장학회 2000 한국결정성장학회지 Vol.10 No.2
도립형 OMVPE 반응기 내부의 기상 온도분포와 OMVPE 전구체들의 농도분포를 in-situ Raman 분광법으로 조사하였다. 운반기체의 회전 Raman 스펙트럼 분석을 통해 반응기 내부의 온도 분포를 측정하였고, 기판 근처에 수직적 온도 구배가 형성됨을 확인할 수 있었다. 또한 진동 Raman 스펙트럼 해석으로부터 전구체의 열분해도를 관찰살 수 있었다. $NH_3$의 경우 800 K 근처에서, TMGa의 경우 650 K 근처에서 열분해가 시작됨을 알 수 있었고, 기판에 매우 근접한 지역에서도 상당량의 전구체가 분해되지 않은 상태로 잔류함을 알 수 있었다. The temperature profiles of gas phase and the concentration profiles of GaN precursors in an inverted OMVPE reactor have been carried out by in-situ Raman spectroscopy. Pure rotational Raman scattering from the carrier gas (rd) was used to determine the temperature profiles in the reactor, and a large temperature gradient perpendicular the susceptor surface was observed. The homogeneous gas phase decompositions of the OMVPE precursors were investigated by the vibrational Raman spectra, and it was found that the pyrolyses of $NH_3$ and TMGa begin above 800 K and 650 K, respectively, but a noticeable amount of precursors remain undecomposed even in the region very close to the susceptor.