• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.222-227
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• 2020

Pb(Zr,Ti)O₃(denoted as PZT) in the perovskite phase is used as a dielectric, piezoelectric, and super appetizer material owing to its ferroelectric properties. A PZT film was formed by an RF magnetron sputtering process by preparing a target composed of Pb_1.3(Zr_0.52Ti_0.48)O₃. The PZT film was formed by dividing the material into a mono-layer PZT produced continuously with the same sputtering power and a bi-layer PZT produced with two-stage sputtering power. The bi-layer PZT consisted of a lower layer produced under low-power sputtering conditions and an upper layer produced under the same conditions as the mono-layer PZT. XRD revealed small amounts of pyrochlore phase in the mono-layer PZT, but only the perovskite phase was detected in the bi-layer PZT. SEM and AFM revealed the upper part of the bi-layer PZT to be more compact and smooth. Moreover, the bi-layered PZT showed superior symmetry polarization and a significantly reduced leakage current of less than 1×10-5 A/cm². This phenomenon observed in bi-layer PZT was attributed to the induction of growth into a pure perovskite phase by suppressing the formation of a pyrochlore phase in the upper PZT layer where the densely formed lower PZT layer was produced sequentially.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.3
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• pp.129-134
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• 2020

Moisture infiltration inside the solar cell module, filling of EVA sheet, melting of the frame seal, and deterioration of power generation performance in the module one year after installation are occurring. Whitening phenomenon, electrode corrosion phenomenon, and dielectric breakdown phenomenon are appearing in solar cell module installed in Korea before 5-7 years, leading to deterioration of power generation performance, and big problems for long-term reliability and long life technology are emerging. Therefore, in order to solve these problems, the development of a micro inverter (MiCrco Inverter Converter, MiC) including the function of securing the durability of the solar cell module and monitoring the aging progress and the solar cell based on the monitoring data from the MiC smart monitoring programs have been proposed to determine the aging of modules. In addition, in order to become a highly efficient solar smart monitoring system through systematic operation management through IT convergence with MiC that has enhanced monitoring function of solar cell module, SoC(System On Chip) in micro inverter is the environment for solar cell module. There is a demand for functions that can detect information in a complex manner and perform communication and control when necessary. Based on these requirements, this paper aims to develop SoC-based low-cost MiC smart photovoltaic system technology.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.2
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• pp.139-147
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• 1994

Orthophosphate crystals were grown by the hydrothermal method and the properties of grown crystals were investigated by means of X-ray diffraction. Vickers hardness tester, etc. The starting powders of $AIPO_4 and GaPO_4 $were prepared as a single phase by the solid state reaction of stoichiometric mixture of $AI_2O_3 or Ga_2O_3$ and $NH_4H_2PO_4$ and the subsequently by the hydrothermal treatment. The hydrothermal conditions for high growth rates of the orthophosphate crystals are as follows: $AlPO_4$ crystal; temperature ranges, between $170$~$200^{\circ}C$; temperatures difference, $15$~$20^{\circ}C;$, hydrothermal solvent, 4m HCl, $GaPO_4 crystal; temperature ranges, between $210 and 240^{\circ}C;$; temperature difference, $25$~$30^{\circ}C; $, hydrothermal solvent, 4m HCl. Morphologies of grown crystals tended to be bounded by (1010), (1011) and (0111) faces at low temperatures, and grew with well developed (0001) faces by increasing the growth temperature. On the other hand, the properties of orthophosphate crystals $(AlPO_4/GaPO_4)$ were as follows: lattice parameters (nm); a=0.494, c=1.094/a=0.490, c=1.105, density (gcm-3); 2.62/3.56, Vickers hardness (Nm^2); $1.02{\times}10^1^0/7.06{\times}10^9$, refractive indices; $ne=1.529{\pm}0.003, no=1.519{\pm}0.003/ne=1.611{\pm}0.006, no=1.599{\pm}0.006, birefringence; {\pm}0.01/{\pm}0.012$, dielectric constant (Fm-1); 6/7.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.709-714
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• 2018

This study researched the reasons for changing polarity in accordance with junction properties in an interface of semiconductors. The contact properties of semiconductors are related to the effect of the semiconductor's device. Therefore, it is an important factor for understanding the junction characteristics in the semiconductor to increase the efficiency of devices. For generation of various junction properties, carbon-doped silicon oxide (SiOC) was deposited with various argon (Ar) gas flow rates, and the characteristics of the SiOC was varied based on the polarity in accordance with the Ar gas flows. Tin-doped zinc oxide (ZTO) as the conductor was deposited on the SiOC as an insulator to research the conductivity. The properties of the SiOC were determined from the formation of a depletion layer by the ionization reaction with various Ar gas flow rates due to the plasma energy. Schottky contact was good in the condition of the depletion layer, with a high potential barrier between the silicon (Si) wafer and the SiOC. The rate of ionization reactions increased when increasing the Ar gas flow rate, and then the potential barrier of the depletion layer was also increased owing to deficient ions from electron-hole recombination at the junction. The dielectric properties of the depletion layer changed to the properties of an insulator, which is favorable for Schottky contact. When the ZTO was deposited on the SiOC with Schottky contact, the stability of the ZTO was improved by the ionic recombination at the interface between the SiOC and the ZTO. The conductivity of ZTO/SiOC was also increased on SiOC film with ideal Schottky contact, in spite of the decreasing charge carriers. It increases the demand on the Schottky contact to improve the thin semiconductor device, and this study confirmed a high-performance device owing to Schottky contact in a low current system. Finally, the amount of current increased in the device owing to ideal Schottky contact.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.284-284
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• 2016

Topological insulator (TI) is a bulk-insulating material with topologically protected Dirac surface states in the band gap. In particular, $Bi_2Se_3$ attracted great attention as a model three-dimensional TI due to its simple electronic structure of the surface states in a relatively large band gap (~0.3 eV). However, experimental efforts using $Bi_2Se_3$ have been difficult due to the abundance of structural defects, which frequently results in the bulk conduction being dominant over the surface conduction in transport due to the bulk doping effects of the defect sites. One promising approach in avoiding this problem is to reduce the structural defects by heteroepitaxially grow $Bi_2Se_3$ on a substrate with a compatible lattice structure, while also preventing surface degradation by encapsulating the pristine interface between $Bi_2Se_3$ and the substrate in a clean growth environment. A particularly promising choice of substrate for the heteroepitaxial growth is hexagonal boron nitride (h-BN), which has the same two-dimensional (2D) van der Waals (vdW) layered structure and hexagonal lattice symmetry as $Bi_2Se_3$. Moreover, since h-BN is a dielectric insulator with a large bandgap energy of 5.97 eV and chemically inert surfaces, it is well suited as a substrate for high mobility electronic transport studies of vdW material systems. Here we report the heteroepitaxial growth and characterization of high quality topological insulator $Bi_2Se_3$ thin films prepared on h-BN layers. Especially, we used molecular beam epitaxy to achieve high quality TI thin films with extremely low defect concentrations and an ideal interface between the films and substrates. To optimize the morphology and microstructural quality of the films, a two-step growth was performed on h-BN layers transferred on transmission electron microscopy (TEM) compatible substrates. The resulting $Bi_2Se_3$ thin films were highly crystalline with atomically smooth terraces over a large area, and the $Bi_2Se_3$ and h-BN exhibited a clear heteroepitaxial relationship with an atomically abrupt and clean interface, as examined by high-resolution TEM. Magnetotransport characterizations revealed that this interface supports a high quality topological surface state devoid of bulk contribution, as evidenced by Hall, Shubnikov-de Haas, and weak anti-localization measurements. We believe that the experimental scheme demonstrated in this talk can serve as a promising method for the preparation of high quality TI thin films as well as many other heterostructures based on 2D vdW layered materials.