• 한국해양공학회지
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• 제24권1호
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• pp.166-171
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• 2010

In this paper, the front-end of a digital receiver with a 25 kHz carrier frequency, 5 kHz symbol rate, and any excess-bandwidth is designed using two basic facts. The first is known as the uniform sampling theorem, which states that the sampled sequence might not suffer from aliasing even if its sampling rate is lower than the Nyquist sampling rate if the analog signal is a bandpass one. The other fact is that if the sampling rate is 4 times the center frequency of the sampled sequence, the front-end processing complexity can be dramatically reduced due to the half of the sampled sequence to be multiplied by zero in the demixing process. Furthermore, the designed front-end is simplified by introducing sub-filters and sub-sampling sequences. The designed front-end is composed of an A/D converter, which takes samples of a bandpass filtered signal at a 20 kHz rate; a serial-to-parallel converter, which converts a sampled bandpass sequence to 4 parallel sub-sample sequences; 4 sub-filter blocks, which act as a frequency shifter and lowpass filter for a complex sequence; 4 synchronized switches; and 2 adders. The designed front-end dramatically reduces the computational complexity by more than 50% for frequency shifting and lowpass filtering operations since a conventional front-end requires a frequency shifting and two lowpass filtering operations to get one lowpass complex sample, while the proposed front-end requires only four filtering operation to get four lowpass complex samples, which is equivalent to one filtering operation for one sample.

• 대한조선학회 특별논문집
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• 대한조선학회 2015년도 특별논문집
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• pp.50-55
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• 2015

Application of newly conceptualized Anti-Splash Devices designed for COT vent pipes were studied on a P/V valve located on the upper deck of an oil carrier vessel. Anti-Splash devices are used in the shipbuilding industry in order to avoid oil overflow and spray accidents caused by excess pressure and vacuum condition in the cargo oil tanks. These conditions are caused by the transverse and longitudinal sloshing forces that arise from ship motion during sea voyages. The main issue with existing Anti-Splash device model is flux at the outlet of the Anti-Splash Device, and so, new conceptual models for the Anti-Splash device were developed and compared to existing Anti-Splash device model using CFD analysis. Transient analysis was used to capture the flow and velocity of each model and a comparative analysis was performed between old and new-concept models. This data was used to determine the optimal design parameters in order to develop an optimized Anti-Splash Device. A Factory acceptance test was performed on the new-concept models in order to verify the performance and efficiency against their design requirements and other criterion. The final step performed was to apply the optimized Anti-Splash Device models for COT vent pipes to an actual vessel and verify performance through a seawater cargo operation during a sea voyage as per the ship owner's request. The patent for the aforementioned device was obtained by the Korean Intellectual property Office dated Dec. 18th,2014.

• JSTS:Journal of Semiconductor Technology and Science
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• 제11권1호
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• pp.40-50
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• 2011

A two-dimensional (2D) analytical model for the potential distribution and threshold voltage of short-channel ion-implanted GaAs MESFETs operating in the sub-threshold regime has been presented. A double-integrable Gaussian-like function has been assumed as the doping distribution profile in the vertical direction of the channel. The Schottky gate has been assumed to be semi-transparent through which optical radiation is coupled into the device. The 2D potential distribution in the channel of the short-channel device has been obtained by solving the 2D Poisson's equation by using suitable boundary conditions. The effects of excess carrier generation due to the incident optical radiation in channel region have been included in the Poisson's equation to study the optical effects on the device. The potential function has been utilized to model the threshold voltage of the device under dark and illuminated conditions. The proposed model has been verified by comparing the theoretically predicted results with simulated data obtained by using the commercially available $ATLAS^{TM}$ 2D device simulator.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.235-238
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• 1996

An inverted double channel AIGaAs/lnGaAs/GaAs heterostructure grown by LP-MOCVD is demonstrated and discussed. Sheet carrier densities in excess of $4.5{\times}10^{12}cm^{-2}$ at 300K are obtained with a hall mobility of $5010cm^2/V{\cdot}s$. The proposed device with a $1.8{\times}200{\mu}m^2$ gate dimension reveals an extrinsic transconductance as high as 320 mS/mm and a saturation current density as high as 820 mA/mm at 300K. This is the highest current density ever reported for GaAs MODFET's with the same gate length. Significantly improvements on gate voltage swing (up to 3.5 V) and on reverse breakdown voltage (-10V) are demonstrated due to inverted structure.

• 한국재료학회지
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• 제13권10호
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• pp.673-676
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• 2003

We have investigated $Al_{x}$ $Ga_{l-x}$ N/GaN epilayers (x = 0.08, 0.15) grown by metal organic vapor phase epitaxy on sapphire with photoluminescence(PL), and persistent photoconductivity(PPC) experiments. An anomalous S-shaped shift behavior of temperature dependencies of PL peak energy is observed for the x = 0.15 sample. In PPC measurement, showed that the dark current recovery time of $Al_{x}$$Ga_{l-x}$ N/GaN epilayers mainly depends on the Al content. These behaviors are usually attributed to the presence of carrier localization states. All these phenomena are explained based on the alloy compositional fluctuations in the $Al_{x}$ /$Ga_{l-x}$ N/ epilayers. The photocurrent quenching observed in PPC measurements for $Al_{x}$ $Ga_{l-x}$ N/ epilayers less than 0.2 $\mu\textrm{m}$ thickness indicates that the presence of metastable state in the bandgap of GaN layer, and that the excess holes in the valence band recombine with free electrons.

• 한국재료학회지
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• 제31권10호
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• pp.586-591
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• 2021

This paper proposes a mathematical model that can calculate the luminescence characteristics driven by alternating current (AC) power using the current-voltage-luminance (I-V-L) properties of organic light emitting devices (OLED) driven by direct current power. Fluorescent OLEDs are manufactured to verify the model, and I-V-L characteristics driven by DC and AC are measured. The current efficiency of DC driven OLED can be divided into three sections. Region 1 is a section where the recombination efficiency increases as the carrier reaches the emission layer in proportion to the increase of the DC voltage. Region 2 is a section in which the maximum luminous efficiency is stably maintained. Region 3 is a section where the luminous efficiency decreases due to excess carriers. Therefore, the fitting equation is derived by dividing the current density and luminance of the DC driven OLED into three regions, and the current density and luminance of the AC driven OLED are calculated from the fitting equation. As a result, the measured and calculated values of the AC driving I-V-L characteristics show deviations of 4.7% for current density, 2.9 % for luminance, and 1.9 % for luminous efficiency.

• Bulletin of the Korean Chemical Society
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• 제21권10호
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• pp.1041-1043
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• 2000

We present the effects of temperature (between 10 K and 298 K) and of hole concentration on the frequency and intensity of characteristic phonons in polycrystalline $La_2CuO_4-related$ compounds using FT-IR spectros-copy. The influences of the concentration of carrier doped on the phonon modes are prominent in the IR spectra of $La_2CuO_4-related$ compounds. For $La_2-xSrxCuO_4({\chi}=$ 0.00, 0.03, 0.07, 0.10, and 0.15) and electrochemically (or chemically) oxidized $La_2CuO_4$, the intensities of the transverse oxygen mode around 680cm $-^1$ which cor-responds mainly to Cu-O(1) stretching vibration in the basal plane of CuO6 octahedron, are decreased and dis-appeared depending on the Sr-substitution rate and the amount of excess oxygen, while the longitudinal oxygen mode around 510 cm $-^1$ corresponding to the Cu-O(2) stretching in the basal plane of CuO6 octahedron are near-ly invariable. In particular, after two cycles of cooling-heating between 10 K and 298 K for these sample, the phonons around 680 cm $-^1$ are blue shif 13-15 cm $-^1$, while the phonons around 510 cm $-^1$ are nearly constant. The introduction of the charge carrier by doping would give rise to the small contraction of CuO6 oc-tahedron as Cu $^3+$ requires a smaller site than Cu $^2+$, which results in the shortening of the Cu-O(1) bond length and Cu-O(2) bond length with the increased La-O(2) bond length. These results in the frequency shift of the characteristic phonons. The IR spectra of $La_2Li0.5Cu0.5O_4$ which exhibits an insulator behavior despite the $Cu^3+$ of nearly 100%, corroborate our IR interpretations. The mode around 710 cm $-^1$ corresponding to Cu-O(1) stretching vibration is still strongly remained even at low temperature (10 K). Thus, we conclude that the con-duction electrons formed within $CuO_2$ planes of $La_2CuO_4-related$ superconductors screen more effectively the transverse oxygen breathing mode around 680 $cm-^1$ depending on the concentration of the doped charge carrier in $La_2CuO_4-related$ compounds, which might use as a superconductivity probe.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.286-289
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• 2001

Single phase CuGaS$_2$ thin film with the highest diffraction peak of (112) at diffraction angle (2$\theta$) of 28.8$^{\circ}$ was made at substrate temperature of 7$0^{\circ}C$, annealing temperature of 35$0^{\circ}C$ and annealing time of 60 min. And second highest (204) peak was shown at diffraction angle (2$\theta$) of 49.1$^{\circ}$. Lattice constant of a and c of that CuGaS$_2$ thin film was 5.37 $\AA$ and 10.54 $\AA$ respectively. The greatest grain size of the thin film was about 1${\mu}{\textrm}{m}$. The (112) peak of single phase of CuGaS$_2$ thin film at annealing temperature of 35$0^{\circ}C$ with excess S supply was appeared with a little higher about 10 % than that of no exces S supply And the resistivity, mobility and hole density at room temperature of p-type CuGaS$_2$ thin film with best crystalline was 1.4 $\Omega$cm, 15 cm2/V . sec and 2.9$\times$10$^{17}$ cm$^{-3}$ respectively. It was known that carrier concentration had considerable effect than mobility on variety of resistivity of the fabricated CuGaS$_2$ thin film, and the polycrystalline CuGaS$_2$ thin films were made at these conditions were all p-type.

• 한국세라믹학회지
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• 제54권4호
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• pp.323-330
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• 2017

To understand the defect chemistry of multiferroic $BiFeO_3-based$ systems, we synthesized nonstoichiometric $Bi_{1+x}FeO_{3{\pm}{\delta}}$ ceramics by conventional solid-state reaction method and studied their structural, dielectric and high-temperature charge transport properties. Incorporation of an excess amount of $Bi_2O_3$ lowered the Bi deficiency in $BiFeO_3$. Polarization versus electric field (P-E) hysteresis loop and dielectric properties were found to be improved by the $Bi_2O_3$ addition. To better understand the defect effects on the multiferroic properties, the high temperature equilibrium electrical conductivity was measured under various oxygen partial pressures ($pO_2{^{\prime}}s$). The charge transport behavior was also examined through thermopower measurement. It was found that the oxygen vacancies contribute to high ionic conduction, showing $pO_2$ independency, and the electronic carrier is electron (n-type) in air and Ar gas atmospheres.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권6호
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• pp.581-588
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• 2013

This paper presents a study of the process temperature dependence of $Al_2O_3$ film grown by thermal atomic layer deposition (ALD) as a passivation layer in the crystalline Si (c-Si) solar cells. The deposition rate of $Al_2O_3$ film maintained almost the same until $250^{\circ}C$, but decreased from $300^{\circ}C$. $Al_2O_3$ film deposited at $250^{\circ}C$ was found to have the highest negative fixed oxide charge density ($Q_f$) due to its O-rich condition and low hydroxyl group (-OH) density. After post-metallization annealing (PMA), $Al_2O_3$ film deposited at $250^{\circ}C$ had the lowest slow and fast interface trap density. Actually, $Al_2O_3$ film deposited at $250^{\circ}C$ showed the best passivation effects, that is, the highest excess carrier lifetime (${\tau}_{PCD}$) and lowest surface recombination velocity ($S_{eff}$) than other conditions. Therefore, $Al_2O_3$ film deposited at $250^{\circ}C$ exhibited excellent chemical and field-effect passivation properties for p-type c-Si solar cells.