• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.260-264
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• 2012

We have investigated the effect of ambient gases on the structural, electrical, and optical characteristics of IZO thin films intended for use as anode contacts in the organic light emitting diodes (OLED) devices. These IZO thin films were deposited on the PES film by radio frequency (RF) magnetron sputtering under different ambient gases (Ar, Ar + O2, and Ar + H2) at room temperature. In order to investigate the influences of the ambient gases, the flow rate of oxygen and hydrogen in argon has been changed from 0.1 sccm to 0.5 sccm, respectively. All the IZO thin film has an (222) preferential orientation regardless of ambient gases. The electrical resistivity of the IZO film increased with increasing O2 flow rate, whereas the electrical resistivity decreased sharply under an Ar + H2 atmosphere and was nearly similar regardless of the H2 flow rate. The change of electrical resistivity with changes in the ambient gas composition was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO substrates made with the configuration of IZO/α-NPD/DPVB/Alq3/LiF/Al in order to elucidate the performance of the IZO substrate. The current density and the luminance of OLED devices with IZO thin films deposited in 0.5 sccm H2 ambient gas are the highest amongst all other films.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.243-243
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• 2010

Low-temperature grown (LTG) InGaAs epilayers were grown by MBE technique for studying a correlation between terahertz (THz) emission and the intrinsic defects. The 1.2-um-thick Be-compensated LTG-InGaAs epilayers were prepared on SI-InP:Fe substrate at $200-250^{\circ}C$, and subsequently in-situ annealed under As environment at $550^{\circ}C$ for 5-30 minutes. The carrier concentration/mobility and the crystalline structure were analyzed by the Hall effect and the x-ray diffraction (XRD), respectively, and the carrier lifetime were determined by the fs time-resolved pump-probe spectroscopy. THz generation from LTG-InGaAs was carried out by a Ti-sapphire laser (800 nm) of a pulse width of 190 fs at a repetition of 76 MHz. Figure shows the spectral amplitude of generated waves in the THz region. As the growth temperature of epilayer increases, the amplitude is enhanced. However, two samples grown at $200^{\circ}C$, as-grown and annealed, show almost no difference in the spectral amplitude. This suggests that the growth temperature is critical in the formation of defect states involved in THz emission. We are now investigating the correlations between the XRD band attributed to defects, the Hall parameter, and the spectral amplitude of generated THz wave.

• Korean Journal of Materials Research
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• v.22 no.6
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• pp.280-284
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• 2012

Bismuth antimony telluride (BiSbTe) thermoelectric materials were successfully prepared by a spark plasma sintering process. Crystalline BiSbTe ingots were crushed into small pieces and then attrition milled into fine powders of about 300 nm ~ 2${\mu}m$ size under argon gas. Spark plasma sintering was applied on the BiSbTe powders at 240, 320, and $380^{\circ}C$, respectively, under a pressure of 40 MPa in vacuum. The heating rate was $50^{\circ}C$/min and the holding time at the sintering temperature was 10 min. At all sintering temperatures, high density bulk BiSbTe was successfully obtained. The XRD patterns verify that all samples were well matched with the $Bi_{0.5}Sb_{1.5}Te_{3}$. Seebeck coefficient (S), electric conductivity (${\sigma}$) and thermal conductivity (k) were evaluated in a temperature range of $25{\sim}300^{\circ}C$. The thermoelectric properties of BiSbTe were evaluated by the thermoelectric figure of merit, ZT (ZT = $S^2{\sigma}T$/k). The grain size and electric conductivity of sintered BiSbTe increased as the sintering temperature increased but the thermal conductivity was similar at all sintering temperatures. Grain growth reduced the carrier concentration, because grain growth reduced the grain boundaries, which serve as acceptors. Meanwhile, the carrier mobility was greatly increased and the electric conductivity was also improved. Consequentially, the grains grew with increasing sintering temperature and the figure of merit was improved.

• Current Photovoltaic Research
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• v.4 no.4
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• pp.150-154
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• 2016

Mg and In co-doped ZnO (MIZO) thin films with transparent conducting characteristics were successfully prepared on glass substrates by RF magnetron sputtering technique. The Influence of different substrate temperature (from RT to $400^{\circ}C$) on the structural, morphological, electrical, and optical properties of MIZO thin films were investigated. The MIZO thin film prepared at the substrate temperature of $350^{\circ}C$ showed the best electrical characteristics in terms of the carrier concentration ($4.24{\times}10^{20}cm^{-3}$), charge carrier mobility ($5.01cm^2V^{-1}S^{-1}$), and a minimum resistivity ($1.24{\times}10^{-4}{\Omega}{\cdot}cm$). The average transmission of MIZO thin films in the visible range was over 80% and the absorption edges of MIZO thin films were very sharp. The bandgap energy of MIZO thin films becomes wider from 3.44 eV to 3.6 eV as the substrate temperature increased from RT to $350^{\circ}C$. However, Band gap energy of MIZO thin film was narrow at substrate temperature of $400^{\circ}C$.

• Electronics and Telecommunications Trends
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• v.36 no.3
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• pp.53-64
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• 2021

As the 5G service market is expected to grow rapidly, the development of high-power, high-efficiency power amplifiers for the 5G communication infrastructure is indispensable. Gallium nitride (GaN) is attracting great interest as a key device in power devices and integrated circuits due to its wide bandgap, high carrier concentration, high electron mobility, and high-power saturation characteristics. In this study, we investigate the technology trends of Ka-band GaN radio frequency (RF) power devices and integrated circuits for operation in the millimeter-wave band of recent 5G mobile communication services. We review the characteristics of GaN RF high electron mobility transistor (HEMT) devices to implement power amplifiers operating at frequencies around 28 GHz and compare the technology of foreign companies with the device characteristics currently developed by the Electronics and Telecommunication Research Institute (ETRI). In addition, the characteristics of Ka-band GaN monolithic microwave integrated circuit (MMIC) power amplifiers manufactured using various GaN HEMT device technologies are reviewed by comparing characteristics such as frequency band, output power, and output power density of integrated circuits. In addition, by comparing the performance of the power amplifier developed by ETRI, the current status and future direction of domestic GaN power devices and integrated circuit technology will be discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.62-65
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• 1995

CdTe crystals were grown by the vertical Bridgman method. P-type DcTe crystals were grown with Cd:Te= 1:1.001 wt. % ratio, while n-type CdTe crystals were 1:1 Also, CdTe:In crystals were investigated, Lattic constants were 6.489${\AA}$ for p-type 6.480${\AA}$for n=type and 6.483${\AA}$ for CdTe:In EPD was 10$\^$-3/-10$\^$4/cm$\^$-2/ for n-, p-type CdTd, 10$\^$4/-10$\^$5/cm$\^$-2 for Cd:Te:In using by E-Ag solution for (111) plane The carrier concentration, the resistivity and the Hall carrier mobility measured by the van der Pauw method were p=5.78${\times}$10$\^$15/cm$\^$-3/, $\rho$=20.2$\Omega$cm, ${\mu}$$\sub$p/=75.6cm$\^$-2/ V$\^$-1/ sec$\^$-1/ for p-typem n=2.98${\times}$10$\^$16/cm$\^$-3/, $\rho$=0.214$\Omega$cm, ${\mu}$$\sub$p/=978.9cm$\^$-2/ V$\^$-1/ sec$\^$-1/ for n-type and n=7.45${\times}$10$\^$16/cm$\^$-3/, $\rho$=1.54 ${\times}$10$\^$3/$\Omega$cm, ${\mu}$$\sub$p/=658.4 cm$\^$-2/ V$\^$-1/ sec$\^$-1/ for CdTe:In crystals, Transmittance of p-type CdTe was 61% that of n-type was 65%, Cd:Te:In showed 60% IR transmittance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.77-80
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• 1995

GaSb crystals were grown by the vertical Bridgman method. P-type GaSb crystals were grown with Ga:Sb=1:1 at % ratio without dopants and with Te, respectively. Also, GaSb:Te crystals were investigated. Lattice constants were 6.117${\AA}$ for p-type. The carrier concentration, the resistivity, and the carrier mobility measured by the van der Pauw method were p≡8 x $10^{16}$$cm^{-3}$, p≡0.20$\Omega$-cm, ${\mu}$$_{n}$≡$400\textrm{cm}^2$$V^{-1}$$sec^{-1}$ for p-type, n≡1 x $10^{17}$$cm^{-3}$, p≡0.15 $\Omega$-cm, ${\mu}$$_{n}$≡$500\textrm{cm}^2$$V^{-1}$$sec^{-1}$ for n-type at 300K. In case of treating with metal ion of $Ru^{+3}$, $Pt^{+1}$, p≡2 x $10^{17}$$cm^{-3}$, p≡0.08$\Omega$-cm, ${\mu}$$_{n}$≡420$\textrm{cm}^2$$V^{-1}$$sec^{-1}$ for p-type, n≡2.5 x $10^{17}$$cm^{-13}$, p≡0.07 $\Omega$-cm, ${\mu}$$_{n}$≡520$\textrm{cm}^2$$V^{-1}$$sec^{-1}$ for n-type were obtained.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.470-470
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• 2013

Recently, active materials such as amorphous silicon (a-Si), poly crystalline silicon (poly-Si), transition metal oxide semiconductors (TMO), and organic semiconductors have been demonstrated for flexible electronics. In order to apply flexible devices on the polymer substrates, all layers should require the characteristic of flexibility as well as the low temperature process. Especially, pentacene thin film transistors (TFTs) have been investigated for probable use in low-cost, large-area, flexible electronic applications such as radio frequency identification (RFID) tags, smart cards, display backplane driver circuits, and sensors. Since pentacene TFTs were studied, their electrical characteristics with varying single variable such as strain, humidity, and temperature have been reported by various groups, which must preferentially be performed in the flexible electronics. For example, the channel mobility of pentacene organic TFTs mainly led to change in device performance under mechanical deformation. While some electrical characteristics like carrier mobility and concentration of organic TFTs were significantly changed at the different temperature. However, there is no study concerning multivariable. Devices actually worked in many different kinds of the environment such as thermal, light, mechanical bending, humidity and various gases. For commercialization, not fewer than two variables of mechanism analysis have to be investigated. Analyzing the phenomenon of shifted characteristics under the change of multivariable may be able to be the importance with developing improved dielectric and encapsulation layer materials. In this study, we have fabricated flexible pentacene TFTs on polymer substrates and observed electrical characteristics of pentacene TFTs exposed to tensile and compressive strains at the different values of temperature like room temperature (RT), 40, 50, $60^{\circ}C$. Effects of bending and heating on the device performance of pentacene TFT will be discussed in detail.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.207-207
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• 2011

Amorphous transparent oxide semiconductors (a-TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). Recently, Nomura et al. demonstrated high performance amorphous IGZO (In-Ga-Zn-O) TFTs.1 Despite the amorphous structure, due to the conduction band minimum (CBM) that made of spherically extended s-orbitals of the constituent metals, an a-IGZO TFT shows high mobility.2,3 But IGZO films contain high cost rare metals. Therefore, we need to investigate the alternatives. Because Aluminum has a high bond enthalpy with oxygen atom and Alumina has a high lattice energy, we try to replace Gallium with Aluminum that is high reserve low cost material. In this study, we focused on the electrical properties of IZO:Al thin films as a channel layer of TFTs. IZO:Al were deposited on unheated non-alkali glass substrates (5 cm ${\times}$ 5 cm) by magnetron co-sputtering system with two cathodes equipped with IZO target and Al target, respectively. The sintered ceramic IZO disc (3 inch ${\phi}$, 5 mm t) and metal Al target (3 inch ${\phi}$, 5 mm t) are used for deposition. The O2 gas was used as the reactive gas to control carrier concentration and mobility. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of IZO:Al thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.

• Journal of the Korean institute of surface engineering
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• v.40 no.3
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• pp.117-124
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• 2007

The ITO films were deposited on glass substrates by RF-superimposed dc reactive magnetron sputtering and were annealed in $N_2$ vacuum furnace with temperatures in the range of $403K{\sim}573K$ for 30 minutes. Electrical, optical and structural properties of ITO films were examined with varying annealing temperatures from 403 K to 573 K. The resistivity of as-deposited ITO films was $5.4{\times}10^{-4}{\Omega}cm$ at the sputter conditions of applied RF/DC power of 200/200 W, $O_{2}$ flow of 0.2 seem and Ar flow of 0.2 seem. As a result of annealing in the temperature range of $403K{\sim}573K$, the crystallization occurred at 423 K that is lower than the crystallization temperature caused by a conventional sputtering method. And the resistivity decreased from $5.4{\times}10^{-4}{\Omega}cm\;to\;2.3{\times}10^{-4}{\Omega}cm$, the carrier concentration and mobility of ITO films increased from $4.9{\times}10^{20}/cm^3\;to\;6.4{\times}10^{20}/cm^3$, from $20.4cm^2/Vsec\;to\;41.0cm^2/Vsec$, respectively. The transmittance of ITO films in visible became higher than 90% when annealed in the temperature range of $423K{\sim}573K$. High quality ITO thin films made by RF-superimposed dc reactive magnetron sputtering and annealing in $N_2$ vacuum furnace will be applied to transparent conductive oxides of the advanced flat panel display.