• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.14-22
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• 2010

The source/channel/drain regions are formed by ion implantation with different dopant types of $n^+/p^{(+)}/n^+$ in the fabrication of the conventional n-type metal-oxide-semiconductor field effect transistor(NMOSFET). In implementing the ultra-small devices with channel length of sub-30 nm, in order to achieve the designed effective channel length accurately, low thermal budget should be considered in the fabrication processes for minimizing the lateral diffusion of dopants although the implanted ions should be activated as completely as possible for higher on-current level. Junctionless (JL) MOSFETs fully capable of the the conventional NMOSFET operations without p-type channel for enlarging the process margin are under researches. In this paper, the optimum design of the JL MOSFET based on silicon nanowire (SNW) structure is carried out by 3-D device simulation and the basic radio frequency (RF) characteristics such as conductance, maximum oscillation frequency($f_{max}$), current gain cut-off frequency($f_T$) for the optimized device. The channel length was 30 run and the design variables were the channel doping concentration and SNW radius. For the optimally designed JL SNW NMOSFET, $f_T$ and $f_{max}$ high as 367.5 GHz and 602.5 GHz could be obtained, respectively, at the operating bias condition $V_{GS}$ = $V_{DS}$ = 1.0 V).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.1
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• pp.11-20
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• 1994

GaAs and AlGaAs epi-layers were grown on semi-insulating (100) GaAs substrate by molecular beam epitaxy (MBE) and their electrical and optical properties have been investigated by several measurements. In undoped GaAs, the p-type GaAs layers with the good surface morphology were obtained under the growth conditions of the substrate temperatures ranging from 570 to $585^{\circ}C$ and the $As_4$/Ga ratios from 17 to 22. In the samples with the growth rates of the ranges of $0.9~1.1 {\mu}m/h$, the impurity concentrations were in the ranges of $1.5{\times}10^{14}~5.6{\times}10^{14}cm^{-3}$ with the Hall mobilities of $590~410cm^2/V-s$. In the Si-doped GaAs, the n-type GaAs layers with low electro trap, only two hole deep levels were observed with uniform doping profiles (<1%). AlGaAs layers with good surface morphology and crystallinity were grown under an optimum condition of the substrate temperature, $600^{\circ}C $. 8 deep level defects were observed between 0.17~0.85eV in undoped AlGaAs layers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.59-65
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• 2006

Al-doped and F-doped ZnO (ZnO : Al & ZnO : F) thin films were coated onto glass substrate by sol-gel method. These films showed c-axis orientation in common, but different I(002)/[I(002) + I(101)] and FWHM (full width at half-maximum). In particular, the grain size of the ZnO : Al films decreased with the increase in the Al-doping concentration, while for the ZnO : F films the grain siae increased up to F 3 at% and then decreased. For the electrical properties, Hall effect measurement was used. The resistivity of the ZnO : Al films and the ZnO : F films were, respectively, $2.9{\times}10^{-2}{\Omega}cm$ at Al 1 at% and $3.3{\times}10^{-1}{\Omega}cm$ at F 3 at%. Moreover compared with ZnO:Al films, ZnO:F films have lower carrier concentration (ZnO : Al $4.8{\times}10^{18}cm^{-3}$, ZnO : F $3.9{\times}10^{16}cm^{-3}$) and higher mobility (ZnO : Al $45cm^2/Vs$, ZnO : F $495cm^2/Vs$). For average optical transmittances, ZnO : Al thin films have $86{\sim}90%$ and ZnO : F films have $77{\sim}85%$ comparatively low.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.576-583
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• 2018

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its band gap is larger than that of silicon and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, porous n-type SiC ceramics fabricated from ${\beta}-SiC$ powder have been found to show a high thermoelectric conversion efficiency in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$. For the application of SiC thermoelectric semiconductors, their figure of merit is an essential parameter, and high temperature (above $800^{\circ}C$) electrodes constitute an essential element. Generally, ceramics are not wetted by most conventional braze metals,. but alloying them with reactive additives can change their interfacial chemistries and promote both wetting and bonding. If a liquid is to wet a solid surface, the energy of the liquid-solid interface must be less than that of the solid, in which case there will be a driving force for the liquid to spread over the solid surface and to enter the capillary gaps. Consequently, using Ag with a relatively low melting point, the junction of the porous SiC semiconductor-Ag and/or its alloy-SiC and/or alumina substrate was studied. Ag-20Ti-20Cu filler metal showed promise as the high temperature electrode for SiC semiconductors.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.216-219
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• 2011

Perovskite manganites such as $RE_{1-x}A_xMnO_3$ (RE = rare earth, A = Ca, Sr, Ba) have been the subject of intense research in the last few years, ever since the discovery that these systems demonstrate colossal magnetoresistance (CMR). The CMR is usually explained with the double-exchange (DE) mechanism, and CMR materials have potential applications for magnetic switching, recording devices, and more. However, the intrinsic CMR effect is usually found under the conditions of a magnetic field of several Teslas and a narrow temperature range near the Curie temperature ($T_c$). This magnetic field and temperature range make practical applications impossible. Recently, another type of MR, called the low-field magnetoresistance(LFMR), has also been a research focus. This MR is typically found in polycrystalline half-metallic ferromagnets, and is associated with the spin-dependent charge transport across grain boundaries. Composites with compositions $La_{0.7}(Ca_{1-x}Sr_x)_{0.3}MnO_3)]_{0.99}/(BaTiO_3)_{0.01}$ $[(LCSMO)_{0.99}/(BTO)_{0.01}]$were prepared with different Sr doping levels x by a standard ceramic technique, and their electrical transport and magnetoresistance (MR) properties were investigated. The structure and morphology of the composites were studied by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). BTO peaks could not be found in the XRD pattern because the amount of BTO in the composites was too small. As the content of x decreased, the crystal structure changed from orthorhombic to rhombohedral. This change can be explained by the fact that the crystal structure of pure LCMO is orthorhombic and the crystal structure of pure LSMO is rhombohedral. The SEM results indicate that LCSMO and BTO coexist in the composites and BTO mostly segregates at the grain boundaries of LCSMO, which are in accordance with the results of the magnetic measurements. The resistivity of all the composites was measured in the range of 90-400K at 0T, 0.5T magnetic field. The result indicates that the MR of the composites increases systematically as the Ca concentration increases, although the transition temperature $T_c$ shifts to a lower range.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1292-1300
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• 1996

In-site X-ray diffraction measurements under electric field up to 20kV/ cm were carried out on PLZT (x/70/30) with x=7.5, 8.0, 8.5, and 10.5 All of PLZT belonged to cubic phases. At x=7.5, 8.0 and 8.5 PLZT behaved as an antiferroelectric under low electric fields up to 4-8 kV/cm. PLZT became ferroelectric at the higher electric fields. The high-temperature measurements on the dielectric constants of PLZT with x=7.5, 8.0 and 8.5 showed that they were similar to relaxor ferroelectrics and underwent a diffuse phase transition from antiferroelectrics to paraelectrics at 50-7$0^{\circ}C$. Their P-E hysteresis curves confirmed that they were antifer-roelectrics. The broad distribution of Curie points suggests that there is a significant disorder of cations and vacances in the crystal structure of those PLZT due to La-substitution. The variation of the lattice strain of PLZT(10.5/70/30) with electic field was very small and did not show any hysteresis confirming that it was paraelectric. The degree of the electric-induced strain variation decreased as La doping increased. In PLZT(7.5/70/30) the intensity of 110 reflection changes sensitively by applying electric field. Some domains with polarization parallel to [110] appeared to be developed in the field-induced ferroelectric phase of the PLZT.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.32-32
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• 2008

Microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of $0.9BaTiO_3-0.1(Bi_{0.5}Na_{0.5})TiO_3$ [BaBiNT] ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free high Curie temperature ($T_c$)(>$160^{\circ}C$) PTC thermistor. The BaBiNT ceramics showed a tetragonal perovskite structure, irrespective of the added amount of $Nb_2O_5$. They also have a homogeneous microstructure. The resistivity of BaBiNT ceramics was gradually decreased by doping $Nb_2O_5$, which might be due to $Nb^{+5}$ ions substituting for $Ti^{+4}$ sites. The PTCR characteristics of BaBiNT ceramics appeared when the amount of doped $Nb_2O_5$ exceeded 0.0025mol%. Moreover, the abrupt grain growth was observed for the 0.03mol% $Nb_2O_5$added BaBiNT ceramics. It showed an especially high $T_c$ of approximately $172^{\circ}C$ and good PTCR characteristics of a high $\rho_{max}/\rho_{min}$ ratio ($2.96\times10^3$), a high resistivity temperature factor (11.40/$^{\circ}C$) along with a relatively low resistivity ($3.5\times10^4\Omega{\cdot}cm$).

• Polymer(Korea)
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• v.33 no.3
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• pp.191-197
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• 2009

We have investigated the effect of strong p-type organic semiconductor $F_4$-TCNQ-doped CuPc hole transport layer on the performance of p-i-n type bulk heterojunction photovoltaic device with ITO/PEDOT:PSS/CuPc: $F_4$-TCNQ(5 wt%)/CuPc:C60(blending ratio l:l)/C60/BCP/LiF/Al, architecture fabricated via vacuum deposition process, and have evaluated the J-V characteristics, short-circuit current ($J_{sc}$), open-circuit voltage($V_{oc}$), fill factor(FF), and power conversion efficiency(${\eta}_e$) of the device. By doping $F_4$-TCNQ into CuPc hole transport layer, increased absorption intensity in absorption spectra, uniform dispersion of organic molecules in the layer, surface uniformity of the layer, and enhanced injection currents improved the current photovoltaic device with power conversion efficiency(${\eta}_e$) of 0.16%, which is still low value compared to silicone solar cell indicating that many efforts should be made to improve organic photovoltaic devices.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.135-139
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• 2015

$Bi_2Te_3-Bi_2Se_3$ alloy which is typical n-type thermoelectric material were grown by traveling heater method (THM) technique. We investigate the effect of the composition of $100-x(Bi_2Te_3)-x(Bi_2Se_3)$ and doping of n-type dopants such as $SbI_3$ and $CdCl_2$. Maximum figure of merit of $Bi_2Te_3-Bi_2Se_3$ alloy was observed with $CdCl_2$ 0.1 wt% (Z: $2.73{\times}10^{-3}/K$) and $SbI_3$ 0.05 wt% (Z: $2.29{\times}10^{-3}/K$). Deviation along the length of $Bi_2Te_3-Bi_2Se_3$ ingot grown by THM method is low, which indicates that the ingot is very homogenized. Also we observed the close relationship of between anisotropy ratio and dopant in the $90(Bi_2Te_3)-10(Bi_2Se_3)$ alloys. And we confirmed the fact that anisotropy ratio exerts thermoelectric performance in $Bi_2Te_3$ based n-type thermoelectric material.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.4
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• pp.178-184
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• 2010

The $12CaO{\cdot}7Al_2O_3$(C12A7) powders were successfully synthesized using combustion method with microwave-assistant and C12A7:H were fabricated by post-annealed process in Ar/H atmosphere. X-ray diffraction patterns and TGDSC were used for investigating to the precursors of crystalline and reaction depending on temperature. C12A7:H that was treated post-annealed process were investigated TG-MS and Hall-measurement for confirming H ions doping and checking electrical resistivity of C12A7:H. H ion substituted to $O^{2-}$ ions in the C12A7 cages were confirmed at $289.5^{\circ}C$ by TG-MS and C12A7:H calcined at $1000^{\circ}C$ in Ar/H=8:2 atmosphere for 8~10 h has low electrical resistivity about $10^2{\Omega}{\cdot}cm$ at room temperature.