• Bulletin of the Korean Chemical Society
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• v.10 no.5
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• pp.418-422
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• 1989

Cadmium-doped indium sesquioxide systems with a variety of CdO mol % were prepared to investigate the effect of doping on the electrical properties of indium sesquioxide. The electrical conductivities of pure $In_2O_3$ and Cd-doped $In_2O_3$ systems were measured in the temperature range from 25 to $1200^{\circ}C$ and $P_O_2$ range from $10^{-7}$ to $10^{-1}$ atm, and the thermoelectric power was measured in the same temperature range. The electrical conductivity and thermopower decreased with increasing CdO mol % indicating that all the samples are n-type semiconductors. The electrical conductivities of pure $In_2O_3$ and lightly doped $In_2O_3$ were considerably affected by the chemisorption $O_2$ at temperatures of 400 to $560^{\circ}C$ and then gaseous oxygen was reversibly chemisorbed at the temperature. The predominant defects in $In_2O_3$ are believed to be triply-charged interstitial indiums at temperatures above $560^{\circ}C$ and oxygen vacancies below $560^{\circ}C$. In Cd-doped $In_2O_3$ systems, cadmium acts as an electron acceptor and inhibits the transfer of lattice indium to interstitial sites, which give rise to the decrease of the electrical conductivity.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.401-405
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• 2004

Undoped SrB $i_2$T $a_2$O$_{9}$, donor-doped Sr$_{0.99}$B $i_2$(Ta$_{0.99}$W$_{0.01}$)$_2$O$_{9}$ and acceptor-doped SrB $i_2$(Ta$_{0.99}$Ti$_{0.01}$)$_2$O$_{8.99$ ceramics were prepared and their microstructure, ferroelectric P-E hysteresis and Curie temperature were investigated. Grain size did not influence P-E hysteresis curve in undoped SrB $i_2$T $a_2$O$_{9}$ ceramics. Donor-Doped Sr$_{0.99}$B $i_2$(Ta$_{0.99}$W$_{0.01}$)$_2$O$_{9}$ ceramics showed more saturated P-E hysteresis curve with larger remanent polarization (P$_{r}$) than undoped SrB $i_2$T $a_2$O$_{9}$ ceramics while acceptor-doped SrB $i_2$(Ta$_{0.99}$Ti$_{0.01}$)$_2$O$_{8.99}$ ceramics led to a pinched P-E hysteresis loop. Larger polarization in donor-doped Sr$_{0.99}$B $i_2$(Ta$_{0.99}$W$_{0.01}$)$_2$O$_{9}$ ceramics resulted from easier domain wall motion by Sr-vacancies.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.41-44
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• 2014

In this paper, we will investigate the activation energies of Nb for $TiO_2$ using Hall effect measurement and photoluminescence (PL) system. Nb-doped $TiO_2$ thin film was grown on $SrTiO_3$ substrate by pulsed laser deposition (PLD) technique. After measurements, activation energies of niobium donor were 14.52 meV in Hall effect measurement, and 6.72 meV in PL measurement, respectively. These results showed different tendencies which are measured from the samples with acceptor materials. Therefore, it is thought that more research on activation energies for dopants of shallow donor level is expected.

• Journal of Powder Materials
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• v.20 no.6
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• pp.474-478
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• 2013

The most general photocatalyst, $TiO_2$ and $WO_3$, are acknowledged to be ineffective in range of visible light. Therefore, many efforts have been directed at improving their activity such as: band-gap narrowing with non-metal element doping and making composites with high specific surface area to effectively separate electrons and holes. In this paper, the method was introduced to prepare a photo-active catalyst to visible irradiation by making a mixture with $TiO_2$ and $WO_3$. In the $TiO_2-WO_3$ composite, $WO_3$ absorbs visible light creating excited electrons and holes while some of the excited electrons move to $TiO_2$ and the holes remain in $WO_3$. This charge separation reduces electron-hole recombination resulting in an enhancement of photocatalytic activity. Added Ag plays the role of electron acceptor, retarding the recombination rate of excited electrons and holes. In making a mixture of $TiO_2-WO_3$ composite, the mixing route affects the photocatalytic activity. The planetary ball-mill method is more effective than magnetic stirring route, owing to a more effective dispersion of aggregated powders. The volume ratio of $TiO_2(4)$ and $WO_3(6)$ shows the most effective photocatalytic activity in the range of visible light in the view point of effective separation of electrons and holes.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.171-171
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• 2010

GaN 기반 Light emitting diodes(LEDs)의 p-type doping layer는 일반적으로 hole을 발생시키는 acceptor로 Mg이 사용하되고 있다. 보통 Mg이 도핑된 p-type GaN은 >$1\;{\Omega}{\cdot}cm$의 저항이 존재하는데 그 이유는 Mg의 열적 이온화를 위한 activation 에너지가 높아서 상온에서 valence band의 hole concentration는 전체 억셉터 농도의 1%가 되지 않기 ��문이다. 본 논문에서는 높은 hole 농도를 얻기 위해서 metalorganic chemical-vapor deposition (MOCVD)를 장비를 사용하여 사파이어 기판의 misorientation-angle에 따른 p-type a-plane(11-20) GaN 특성을 분석하였다. misorientation-angle은 c축 방향으로 $+0.15^{\circ}$, $-0.15^{\circ}$, $-0.2^{\circ}$, $-0.4^{\circ}$ off된 r-plane(1-102) 사파이어 기판 을 사용하였다. p-type 도핑물질로 bis-magnesium (Cp2Mg) 소스를 사용하였고 성장 과정중 발생하는 hydrogen passivation으로 인한 Mg-H complexes현상을 해결하기위해 conventional furnace annealing (CFA)와 rapid thermal annealing (RTA)를 이용하여 열처리 공정을 진행하였다. 열처리 공정은 Air와 N2 분위기에서 $650^{\circ}C$에서 $900^{\circ}C$ 사이의 다양한 온도에서 수행하였고 Hall 측정을 위해 Ni을 전극 물질로 사용하였다. 상온에서 Accent HL5500IU Hall system을 사용하여 hole concentration, mobility, specific resistance을 측정하였다. 열처리 공정 후 Hall측정 결과 $+0.15^{\circ}$, $-0.15^{\circ}$, $-0.2^{\circ}$, $-0.4^{\circ}$ off된 각 샘플들은 온도, 시간, 분위기에 따라 hole concentration ($7.4{\times}10^{16}cm^{-3}{\sim}6{\times}10^{17}cm^{-3}$), mobility(${\mu}h=\;1.72\;cm^2/V-s\;{\sim}15.2\;cm^2/V-s$), specific resistance(4.971 ohm-cm ~8.924 ohm-cm) 가 변화됨을 확인 할 수 있었다. 또한 광학적 특성을 분석하기 위해 Photoluminescence (PL)을 측정하였다.

• Bulletin of the Korean Chemical Society
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• v.15 no.12
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• pp.1058-1064
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• 1994

Mn/In$_2O_3$ systems with a variety of Mn mol${\%}$ were prepared to investigate the effect of Mn-addition on the catalytic activity of Mn/In$_2O_3$ in the oxidative coupling of methane. The oxidative coupling of methane was examined on pure In$_2O_3$ and Mn/In$_2O_3$ catalysts by cofeeding gaseous methane and oxygen under atmospheric pressure between 650 and 830 $^{\circ}C$. Although pure In$_2O_3$ showed no C$_2$ selectivity, both the C$_2$ yield and the C$_2$ selectivity were increased by Mn-doping. The 5.1 mol${\%}$ Mn-doped In$_2O_3$ catalyst showed the best C$_2$ yield of 2.6${\%}$ with a selectivity of 19.1${\%}$. The electrical conductivities of pure and Mn-doped In$_2O_3$ systems were measured in the temperature range of 25 to 100 $^{\circ}C$ at PO$_2$'S of 1 ${\times}$ 10$^{-7}$ to 1 ${\times}$ 10 $^{-1}$ atm. The electrical conductivities were decreased with increasing Mn mol${\%}$ and PO$_2$, indicating the specimens to be n-type semiconductors. Electrons serve as the carriers and manganese can act as an electron acceptor in the specimens. Manganese ions doped in In$_2O_3$ inhibit the ionization of neutral interstitial indium or the transfer of lattice indium to interstitial sites and increase the formation of oxygen vacancy, giving rise to the increase of the concentration of active oxygen ion on the surface. It is suggested that the active oxygen species adsorbed on oxygen vacancies are responsible for the activation of methane.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.87-87
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• 2010

Photoelectrochemical (PEC) systems are promising methods of producing H2 gas using solar energy in an aqueous solution. The photoelectrochemical properties of numerous metal oxides have been studied. Among them, the PEC systems based on TiO2 have been extensively studied. However, the drawback of a PEC system with TiO2 is that only ultraviolet (UV) light can be absorbed because of its large band gap (3.2 - 3.4 eV). Two approaches have been introduced in order to use PEC cells in the visible light region. The first method includes doping impurities, such as nitrogen, into TiO2, and this technique has been extensively studied in an attempt to narrow the band gap. In comparison, research on the second method, which includes visible light water splitting in molecular photosystems, has been slow. Mallouk et al. recently developed electrochemical water-splitting cells using the Ru(II) complex as the visible light photosensitizer. the dye-sensitized PEC cell consisted of a dye-sensitized TiO2 layer, a Pt counter electrode, and an aqueous solution between them. Under a visible light (< 3 eV) illumination, only the dye molecule absorbed the light and became excited because TiO2 had the wide band gap. The light absorption of the dye was followed by the transfer of an electron from the excited state (S*) of the dye to the conduction band (CB) of TiO2 and its subsequent transfer to the transparent conducting oxide (TCO). The electrons moved through the wire to the Pt, where the water reduction (or H2 evolution) occurred. The oxidized dye molecules caused the water oxidation because their HOMO level was below the H2O/O2 level. Organic dyes have been developed as metal-free alternatives to the Ru(II) complexes because of their tunable optical and electronic properties and low-cost manufacturing. Recently, organic dye molecules containing multi-branched, multi-anchoring groups have received a great deal of interest. In this work, tri-branched tri-anchoring organic dyes (Dye 2) were designed and applied to visible light water-splitting cells based on dye-sensitized TiO2 electrodes. Dye 2 had a molecular structure containing one donor (D) and three acceptor (A) groups, and each ended with an anchoring functionality. In comparison, mono-anchoring dyes (Dye 1) were also synthesized. The PEC response of the Dye 2-sensitized TiO2 film was much better than the Dye 1-sensitized or unsensitized TiO2 films.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.107-112
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• 1999

The ZnSe/GaAs epilayers were grown by RF reactive sputtering. In order to obtain the optimum condition of the growth, we have studied the dependence of Ar pressure, input power of sputter, temperature of substrate, and the distande between substrate and target. Through the observation of the grown epilayer via electronic microscope, we confirmed that the layer's surface was uniform and the boundary of the substrate and the layer was well defined. The defotmation of lattice distortion and the distortion ratio were obtained by DCRC measurements. From mrasurements of photoluminescence, in the ZnSe/GaAs sample without injection of $N_2$gas, we found that the intensity of bound exciton $I_2$is stronger than that of $I_1$and the bound exiton $I_1$represents the deep acceptor level, $I_1\;^d$. On the other hand, in the ZnSe/GaAs sample with injection of$N_2$gas, the peak of$I_1$ was much higher than that of the $I_2$and the half width appeared to be narrow. We concluded that the p-type of ZnSe/GaAs epilayer was grown successfully, because of stronger peak of the bound exciton $I_1$due to the $N_2$dopping.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.413-418
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• 2005

Perovskite $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,Ti)O_3[PNN-PZT]$ ceramics were synthesized by conventional ceramic processing technique. In order to modify piezoelectric properties for sensor application in this system, NiO addition was considered to provide $Ni^{+2}$ as an acceptor, which was known to occupy with B site in the structure. The effect of NiO addition up to $8\;mol\%$ on the following piezoelectric properties as well as sintering properties was investigated. When NiO added more than $1\;mol\%$, average grain size was decreased and second phase was found to form. Moreover, the second phase caused decrease in relative dielectric constant $(\varepsilon_{33}T/\varepsilon0)$, electro-mechanical coupling factor $(k_p)$, and piezoelectric charge constant $(d_{33})$, while increasing mechanical quality factor $(Q_m)$. When $1\;mol\%$ NiO was added, density, dielectric properties and piezoelectric properties were abruptly increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.596-601
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• 2020

Silicon carbide is considered a potentially useful material for high-temperature electronic devices because of its large band gap energy and p-type or n-type conduction that can be controlled by impurity doping. Accordingly, the thermoelectric properties of -SiC powder prepared by refined diatomite were investigated for high value-added applications of natural diatomite. -SiC powder was synthesized by a carbothermal reduction of the SiO₂ in refined diatomite using carbon black. An acid-treatment process was then performed to eliminate the remaining impurities (Fe, Ca, etc.). n-Type semiconductors were fabricated by sintering the pressed powder at 2000℃ for 1~5h in an N2 atmosphere. The electrical conductivity increased with increasing sintering time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The carrier compensation effect caused by the remaining acceptor impurities (Al, etc.) in the obtained -SiC had a deleterious influence on the electrical conductivity. The absolute value of the Seebeck coefficient increased with increasing sintering time, which might be due to a decrease in the stacking fault density accompanied by grain or crystallite growth. On the other hand, the power factor, which reflects the thermoelectric conversion efficiency of the present work, was slightly lower than that of the porous SiC semiconductors fabricated by conventional high-purity -SiC powder, it can be stated that the thermoelectric properties could be improved further by precise control of an acid-treatment process.