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Structural Investigations of MBE-Grown InAs Layers on GaAs
Sung-ManKim,Sang-heonLee,HowoonKim,Jang-KyooShin,Jae-YoungLeem,Jong-SuKim,Jin-SooKim 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.40 No.1
High-quality InAs films were grown by varying GaAs the buffer layer thickness and using different substrates, both 2-tilted toward the [0 11] and non-tilted GaAs(100) substrate, by molecular beam epitaxy (MBE). Their electrical and structure properties were investigated by Hall measurements, transmission electron microscopy (TEM) and high-resolution X-ray diraction (HRXRD). The 0.5- m InAs film grown on a 2-tilted GaAs substrate and the 1-m InAs lm on non-tilted GaAs substrate had electron mobilities of 10,952 cm2/Vs and 11,944 cm2/Vs, respectively, with same Si doping concentration at room temperature. TEM images showed that high-quality InAs epitaxial layers were obtained with reduced dislocation density at the InAs/GaAs interface.
Development of NBCO Coated Conductor by Using Superconductor Technology
Sang-HeonLee 한국전기전자재료학회 2003 Transactions on Electrical and Electronic Material Vol.4 No.4
NBCO thin films have been fabricated by magnetron sputtering technique on heated SrTiO3 substrates. The oxidation and crystallization of the films were strongly dependent on the distance between the targets and the substrate, as well as on the oxygen partial pressure. The critical temperatures were above 80K for the films prepared under the condition of a small target to substrate gap, in spite of a very low oxygen pressure of 0.2Pa. The results suggest the importance of the activated oxygen uptake into the films during sputtering.
Dielectric ProPerties of Zr-doped(Ba,Sr,Ca)TiO3 Thick Films for Microwave Phase Shifters
Sung-GapLee,Sang-HeonLee 한국전기전자재료학회 2003 Transactions on Electrical and Electronic Material Vol.4 No.2
(Ba,Sr,Ca)TiO3 powders, prepared by the sol-gel method, were mixed with organic binder and the BSCT thick films were fabricated by the screen printing techniques on alumina substrates. All the BSCT thick films, sintered at 1420oC, showed the typical XRD patterns of a perovskite polycrystalline structure. The average grain sizes decreased with increasing amounts of ZrO2, and the BSCT(40/40/20) thick films doped with 2wt% MnO2 showed a value of 8mm. The thickness of thick films by four-cycle on printing/drying was approximately 95mm. The relative dielectric constant decreased with increasing Ca content and MnO2 doping amount. The relative dielectric constant, dielectric loss and tunability of the BSCT(50/40/10) thick films doped with 2.0wt% ZrO2 were 772, 0.184% and 15.62%, respectively.
Dielectric Properties of BSCT Thick Films for Microwave Device Applications
이성갑,김창일,김정필,Sang-HeonLee 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
(Ba$_{0.6-x}$Sr$_{0.4}$Ca$_x$)TiO$_3$ (BSCT) ($x$ = 0.10, 0.15, and 0.20) powders, prepared by using the sol-gel method, were mixed with an organic vehicle, and BSCT thick films were fabricated on alumina substrates by using screen printing techniques and BSCT paste. The structural and the dielectric properties were investigated for various composition ratios and BSCT powder contents. All the BSCT calcined powders showed a homogeneous structure without the presence of a second phase. The thickness of the BSCT thick films obtained by four printings were approximately 120 $\mu$m. The Curie temperature and the dielectric constant at room temperature decreased with increasing Ca content. The relative dielectric constant, the dielectric loss, and the tunability of the BSCT(50/40/10) specimen, which was mixed with a 70.0-wt\% BSCT powder content and measured at 1 MHz, were about 910, 0.46 \%, and 9.28 \% at 30 kV/cm, respectively.