• Journal of the Mineralogical Society of Korea
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• v.23 no.3
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• pp.267-272
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• 2010

High pressure x-ray diffraction patterns of ${\alpha}$-cristobalite gallium phosphate ($GaPO_4$) were acquired up to 8.9 GPa at room temperature using Mao-Bell type diamond anvil cell with high flux synchrotron radiation. Starting orthorhombic phase (phase-I) shows the splitting of peak which is possibly resulted from the pressure induced orientation disorder of the framework structure of tetrahedra. This is designated as phase-I'. This phase transforms to the orthorhombic high pressure phase-III between 2 and 3 GPa. Present phase transition sequence is not in accord with the recent high pressure X-ray diffraction results performed on the same starting sample (Ming et al., 2007). X-ray pattern of the unloaded sample to ambient pressure shows that the structure retains that of the high pressure phase prior to decompression.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.1
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• pp.8-14
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• 2014

In this study, we investigated synthesis and characteristics of gallium oxide ($Ga_2O_3$) powders prepared by precipitation method. $Ga_2O_3$ powders were synthesized using $Ga(NO_3)_3$ as a starting material and $NH_4OH$ as a precipitant. The oxidation temperature of $Ga(OH)_3$ and phase transition temperature of $Ga_2O_3$ was revealed using TG-DSC analysis. The crystal structural change of $Ga_2O_3$ powders was investigated by XRD analysis. The morphologies and size distributions of $Ga_2O_3$ particles were analyzed using SEM.

• Tuberculosis and Respiratory Diseases
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• v.41 no.6
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• pp.651-657
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• 1994

Asbestos is widely used in the textile, asbestos cement, construction products, friction material, paper products, insulation products, chemical and plastic products because of its heat resistance, flexibility, tensile strength, and texturability. It is now generally recognized that longterm and excessive inhalation of asbestos dust causes asbestosis, lung cancer, malignant mesothelioma and malignancies in other organs such as cancer of gastrointestinal tract, leukemia, lymphoma. Although eighty thousand tons of asbestos has been annually consumed since 1979 in korea, it has not been reported asbestos and lung cancer by asbestos dust so far, while a case of mesothelioma was officially diagnosis as a occupational disease at 1993. We experienced firstly a case of asbestosis and lung cancer caused simultanously by occupational asbestos exposure 11 years, which was confirmed by chest x-ray, pulmonary function test, chest CT and HRCT, bronchoalveolar lavage, and gallium scan. And so We present a case of asbestosis, pleural effusion and lung cancer with a review literature.

• Korean Journal of Crystallography
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• v.8 no.1
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• pp.33-37
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• 1997

The optical properties of (1210) GaN epitaxy films grown on the (1012) $\alpha-A1_2O_3$ substrates have been studied. The hetero-epitaxy films were grown by the halide vapor phase epitaxy (HVPE) method using $Ga/HC1/NH_3/He$ system at $990^{\circ}C$. XRD, RHEED and SEM are used for the identification of the hetero-epitaxy films structure and surface morphology. The confirmed (1210) GaN epitaxy films were characterized by PL and Raman. By the Raman scattering, the active phonon modes of single-phase GaN films are varied with the arrangement of both polarization and propagation directions of laser beam with reference to the axis in single-phase crystal films. The Y(Z, Y & Z) X geometry allows scattering pat-terns of $A_1(TO)=533\;cm^{-1},\;E_1(TO)=559\;cm^{-1}\;and\;E_2=568 cm^{-1}$ modes, whereas in the Z(Y, Y & Z) X geometry the only $E_2$ mode are observed.

• Journal of electromagnetic engineering and science
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• v.14 no.3
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• pp.284-292
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• 2014

This paper presents a characteristic evaluation of commercial gallium nitride (GaN) transistors having two different gate-lengths of $0.4-{\mu}m$ and $0.25-{\mu}m$ in the design of a class-S power amplifier (PA). Class-S PA is operated by a random pulse-width input signal from band-pass delta-sigma modulation and has to deal with harmonics that consider quantization noise. Although a transistor having a short gate-length has an advantage of efficient operation at higher frequency for harmonics of the pulse signal, several problems can arise, such as the cost and export license of a $0.25-{\mu}m$ transistor. The possibility of using a $0.4-{\mu}m$ transistor on a class-S PA at 955 MHz is evaluated by comparing the frequency characteristics of GaN transistors having two different gate-lengths and extracting the intrinsic parameters as a shape of the simplified switch-based model. In addition, the effectiveness of the switch model is evaluated by currentmode class-D (CMCD) simulation. Finally, device characteristics are compared in terms of current-mode class-S PA. The analyses of the CMCD PA reveal that although the efficiency of $0.4-{\mu}m$ transistor decreases more as the operating frequency increases from 955 MHz to 3,500 MHz due to the efficiency limitation at the higher frequency region, it shows similar power and efficiency of 41.6 dBm and 49%, respectively, at 955 MHz when compared to the $0.25-{\mu}m$ transistor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.6
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• pp.646-652
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• 2014

This paper presents a design and fabrication of Ku-band power amplifier using Gallium Nitride High Electron Mobility Transistor (GaN HEMT) die. In order to fabricate the low-cost Ku-band power amplifier, a Printed Circuit Board(PCB) was used for input/output matching circuits instead of manufacturing process to use an expensive substrate. The measured output power is 42.6 dBm, the drain efficiency is 37.7 % and the linear gain is 7.9 dB under pulse operation at the frequency of 14.8 GHz. Under the continuous wave(CW) test, the output power is 39.8 dBm, the drain efficiency is 24.1 % and the linear gain is 7.2 dB.

• Journal of electromagnetic engineering and science
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• v.17 no.2
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• pp.105-107
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• 2017

The self-biasing circuit through a feedback resistor is applied to a gallium nitride (GaN) distributed power amplifier (PA) monolithic microwave circuit (MMIC). The self-biasing circuit is a useful scheme for biasing depletion-mode compound semiconductor devices with a negative gate bias voltage, and is widely used for common source amplifiers. However, the self-biasing circuit is rarely used for PAs, because the large DC power dissipation of the feedback resistor results in the degradation of output power and power efficiency. In this study, the feasibility of applying a self-biasing circuit through a feedback resistor to a GaN PA MMIC is examined by using the high operation voltage of GaN high-electron mobility transistors. The measured results of the proposed GaN PA are the average output power of 41.1 dBm and the average power added efficiency of 12.2% over the 6-16 GHz band.

• Resources Recycling
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• v.14 no.2
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• pp.28-32
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• 2005

By using thermal decomposition method, the preliminary experiments for recovery of metallic Ga from GaAs scraps produced in the manufacturing of compound semiconductors were carried out in laboratory(200 g/batch) scales. From these results, decomposition appratus with packed tower was constructed in commercial scale(30 kg/batch). The decomposition rate of GaAs increased with raising decomposition temperature, but the yield of Ga decreased over 1000$^{\circ}C. As a result, the optimum decomposition temperature was 1000~1050$^{\circ}C when the pressure of decomposition reactor was 2~2.5${\times}10^{-2} mmHg, and the yield of Ga was about 89 wt.%. The commercial decomposition apparatus was designed with packed tower because the partial pressure of As in vapor state was not reduced even if the temperature of As vapor was decreased. The recovery yield of Ga from GaAs scraps in large scale experiment showed 99%.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.360-365
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• 1992

Ga-doped polycrystalline ZnO films on glass substrates were prepared by sputtering the targets, which had been prepared by sintering discs consisting of ZnO powder and various amounts of G$a_2O_3$, to investigate the effects of gallium doping and sputtering conditions on electrical properties. Optimizing the RF power density, argon gas pressure and gallium content, transparent Ga-doped ZnO films with resistivity less than 1$0^{-3}$ohm-cm are obtained. Electron concentration of undoped and Ga-doped ZnO films are order of $10^{18}$, $10^{21}$/c$m^2$respectively. After heat treatment in air and $N_2atmosphere, $ the resistivity of Ga-doped ZnO films increases by about two orders of magnitude. The optical transmission is above 80% in the visible range and the optical band widens as the Ga content increases.