• Journal of Magnetics
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• v.1 no.1
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• pp.46-50
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• 1996

Highly oriented ${BaFe_{12}{O_{19}$ films were obtained by a KrF excimer laser ablation technique using (110)$(012){Al_2}{O_3}$(001)$(012){Al_2}{O_3}$ and $(012){Al_2}{O_3}$ substrates, respectively.The degree of alignment of more than 95% were achieved for (100) on (110)$(012){Al_2}{O_3}$ and (001)$(001){Al_2}{O_3}$ planes, and heteroepitaxial films of (114) on (012)$(012){Al_2}{O_3}$were possible to be grown with a lasing energy density of 6.67 J/$cm^2$ at an oxygen partial pressure ${PO_2}$ of 900 mTorr. The best magnetic properties were obtained from the as-deposited films at the substrate temperature of $700^{\circ}C$, and post annealing treatment was not needed to enhance the magnetic properties. Experimentally saturated magnetization ($4_pi M_S$) of 3600~3800 Gauss and coercivities $(H_c)$ of 3050~3080 Oe, which approach 85% of those of Ba-ferrite bulk composed of single domain particles, were obtained in this study.

• Journal of the Korean Chemical Society
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• v.40 no.3
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• pp.167-172
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• 1996

For the preparation of single-crystalline GaN film, heteroepitaxial growth on a sapphire substrate was carried out by halide vapor phase epitaxy(HVPE) method. The resulting GaN films showed n-type conductivity. The insulator type GaN film was made by doping with Zn(acceptor dopant), which showed emission peaks around 2.64 and 2.43 eV. The result of this study indicates that GaN can be obtained in an epitaxial structure of MIS(metal-insulator-semiconductor) junction. The observed data are regarded as fundamental in developing GaN epitaxial films for light emitting devices of hetero-structure type.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.700-704
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• 2003

This paper describes on characteristics of 2" 3C-SiC wafer bonding using PECVD (plasma enhanced chemical vapor deposition) oxide and HF (hydrofluoride acid) for SiCOI (SiC-on-Insulator) structures and MEMS (micro-electro-mechanical system) applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si (001) wafer by thermal wet oxidation and PECVD process, successively. The pre-bonding of two polished PECVD oxide layers made the surface activation in HF and bonded under applied pressure. The bonding characteristics were evaluated by the effect of HF concentration used in the surface treatment on the roughness of the oxide and pre-bonding strength. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by ATR-FTIR (attenuated total reflection Fourier transformed infrared spectroscopy). The root-mean-square suface roughness of the oxidized SiC layers was measured by AFM (atomic force microscope). The strength of the bond was measured by tensile strength meter. The bonded interface was also analyzed by IR camera and SEM (scanning electron microscope), and there are no bubbles or cavities in the bonding interface. The bonding strength initially increases with increasing HF concentration and reaches the maximum value at 2.0 ％ and then decreases. These results indicate that the 3C-SiC wafer direct bonding technique will offers significant advantages in the harsh MEMS applications.ions.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.401-405
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• 1994

The chemical composition and electrical properties were investigated for epitaxially crystallized $(Ba_{0.5}Sr_{0.5})Tio_3$ (BST) films deposited on Pt and $YBa_Cu_3O_{7-x}$(YBCO) electrodes by laser ablation technique. The crystalline quality of the heteroepitaxial BST films deposited on Pt bottom electrode was found to be better than that of BST film on YBCO electrode by the RBS analysis. Films deposited at $600^{\circ}C$ on Pt electrode showed a dielectric constant of 320 and a dissipation factor of 0.023 at 100kHz. Leakage current density of BST films on Pt electrode was smaller than that on YBCO bottom electrode. Their leakage current density was about 0.8$\mu \; A/ \textrm{cm}^2$ at an applied electric field of 0.15MV/cm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.9
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• pp.810-814
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• 2005

[ $Pb(Zr_{0.2}Ti_{0.8})O_3/SrRuO_3$ ] heteroepitaxial thin films were deposited at various temperatures on single crystal $SrTiO_3$ substrates by pulsed laser deposition and characterized for the microstructural and ferroelectric properties. The $SrTiO_3$ substartes etched by buffered oxide etch $(pH{\thickapprox}5.8)$ solution for 20s followed by the thermal annealing at $1000^{\circ}C$ for 1h showed the terrace ledges with a 0.4nm height. The $SrRuO_3$ bottom electrodes with a thickness of 52nm grown on $SrTiO_3$ single crystal also exhibit a terrace ledge similar to that of $SrTiO_3$. The PZT thin films were grown with an epitaxial relationship and showed typical P-E hysteresis loops shown at the epitaxial films. The 56nm thick-PZT films deposited at $650^{\circ}C$ exhibit a remanent polarization $(p_r)$ of $80{\mu}C/cm^2$ and a coercive field $(E_c)$ of 160kV/cm.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.280-280
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• 2014

We report the fabrication and electroluminescent characteristics of GaN/InxGa1-xN microdonut-shaped light-emitting diode (LED) microarrays as variable-color emitters. The diameter, width, height, and period of the GaN microdonuts were controlled by their growth parameters and the geometrical factors of the growth mask patterns. For the fabrication of microdonut LEDs, p-GaN/p-AlxGa1-xN/u-GaN/u-InxGa1-xN heteroepitaxial layers were coated on the entire surface of n-GaN microdonuts. The microdonut LED arrays showed strong light emission, which could be seen with the unaided eye under normal room illumination. Additionally, magnified optical images of microdonut LED arrays exhibited microdonut-shaped light emissions having spatially resolved blue and green colors. Their electroluminescence spectra had two dominant peaks at 460 and 560 nm. With increasing applied voltage, the intensity of the blue emission peak increased much faster than that of the green emission peak, indicating that the color of the LEDs is tunable. We also demonstrated that EL spectra of the devices could be controlled by changing the size of microdonut LEDs. What we want to emphasize here with the microdonut LEDs is that they have additional inner sidewall facets which did not exist for other typical three-dimensional structures including nanopyramids and nanorods, and that InxGa1-xN single quantum well formed on the inner sidewall facets had unique thickness and chemical composition, which generated additional EL color. The origin of the electroluminescence peaks was investigated by structural characterizations and chemical analyses.

• Corrosion Science and Technology
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• v.11 no.1
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• pp.9-14
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• 2012

The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This study presents a characterization result on the inhibition layer formed on C-Mn-Cr and C-Mn-Si dual-phase steels after a short time galvanizing. The samples were annealed at $800^{\circ}C$ for 60 s in $N_{2}$-10% $H_{2}$ atmosphere with a dew point of $-30^{\circ}C$, and were then galvanized in a bath containing 0.2 %Al. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) was employed for characterization. The TEM electron diffraction shows that only $Fe_{2}Al_{5}$ intermetallic phase was formed. No orientation relationship between the $Fe_{2}Al_{5}$ phase and the steel substrate could be identified. Two peaks of Al 2p photoelectrons, one from metallic aluminum and the other from $Al^{3+}$ ions, were detected in the inhibition layer, indicating that the layer is in fact a mixture of $Fe_{2}Al_{5}$ and $Al_{2}O_{3}$. TEM/EDS analysis verifies the existence of $Al_{2}O_{3}$ in the boundaries of $Fe_{2}Al_{5}$ grains. The nucleation of $Fe_{2}Al_{5}$ and the reduction of the surface oxide probably proceeded concurrently on galvanizing, and the residual oxides prohibited the heteroepitaxial growth of $Fe_{2}Al_{5}$.

• Journal of the Korean Magnetics Society
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• v.19 no.4
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• pp.126-132
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• 2009

We have studied physical properties of MnAs thin films grown by Molecular-Beam Epitaxy as well as their post-growth annealing effects. The samples grown at $600^{\circ}C$ show the preferred crystal orientation of type-B independent of substrate whereas type-A is observed for the samples grown at below $200^{\circ}C$. The sample grown at $600^{\circ}C$ on GaAs(001) substrate is magnetized to only one direction even on the easy axis of magnetization. The magnetic properties are vastly enhanced after post-growth annealing for both MnAs/Si(001) sample with no ferromagnetism and ferromagnetic MnAs/GaAs(001) grown at $200^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.7
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• pp.573-578
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• 2003

Low temperature selective epitaxial growth of Si and SiGe has been obtained using an industrial single wafer chemical vapor deposition module operating at reduced pressure. Epitaxial Si and heteroepitaxial SiGe deposition with Ge content about 20 % has been studied as extrinsic base for self-aligned heterojunction bipolar transistors(HBTs), which helps to reduce the parasitic resistance to obtain higher maximum oscillation frequencies(f$\_$max/). The dependence of Si and SiGe deposition rates on exposed windows and their evolution with the addition of HCl to the gas mixture are investigated. SiH$_2$Cl$_2$ was used as the source of Si SEG(Selective Epitaxial Growth) and GeH$_4$ was added to grow SiGe SEG. The addition of HCl into the gas mixture allows increasing an incubation time even low growth temperature of 675∼725$^{\circ}C$. In addition, the selectivity is enhanced for the SiGe alloy and it was proposed that the incubation time for the polycrystalline deposit on the oxide is increased probably due to GeO formation. On the other hand, when only SiGe SEG(Selective Epitaxial Growth) layer is used for extrinsic base, it shows a higher sheet resistance with Ti-silicide because of Ge segregation to the interface, but in case of Si or Si/SiGe SEG layer, the sheet resistance is decreased up to 70 %.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.442-453
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• 2023

Tandem or multijunction solar cells (MJSCs) can convert sunlight into electricity with higher efficiency (η) than single junction solar cells (SJSCs) by dividing the solar irradiance over sub-cells having distinct bandgaps. The efficiencies of various common SJSC materials are close to the edge of their theoretical efficiency and hence there is a tremendous growing interest in utilizing the tandem/multijunction technique. Recently, III-V materials integration on a silicon substrate has been broadly investigated in the development of III-V on Si tandem solar cells. Numerous growth techniques such as heteroepitaxial growth, wafer bonding, and mechanical stacking are crucial for better understanding of high-quality III-V epitaxial layers on Si. As the choice of growth method and substrate selection can significantly impact the quality and performance of the resulting tandem cell and the terminal configuration exhibit a vital role in the overall proficiency. Parallel and Series-connected configurations have been studied, each with its advantage and disadvantages depending on the application and cell configuration. The optimization of both growth mechanisms and terminal configurations is necessary to further improve efficiency and lessen the cost of III-V on Si tandem solar cells. In this review article, we present an overview of the growth mechanisms and terminal configurations with the areas of research that are crucial for the commercialization of III-V on Si tandem solar cells.