• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.82-85
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• 2000

The less sensitive structure to the surface effect has been presented utiliting an undoped GaAs layer on the n-GaAs channel. The undoped layer has been found to be effective to supress the frequency dispersion phenomena caused by a surface trapping effect and to raise the MESFET's performance. The gate structure, with an undoped layer underneath the gate metal has been found to be effective to improve the breakdown voltage. GaAs MESFETS with different physical structures are fabricated and DC characteristics are measued. GaAs MESFET's are fabricated on epi-wafers which have an undoped GaAs layer in between n+ and n GaAs layers grown by MBE.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.97-100
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• 2002

$CdGaInS_{4}:Er^{3+}$ single crystal crystallized in the rhombohedral. with lattice constants a = 3.899 $\AA$ and c = 36.970 $\AA$ for $CdGaInS_{4}:Er^{3+}$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of this compound had a direct and indirect band gaps. the direct and indirect energy gaps are found to be 2.665 and 2.479eV for $CdGaInS_{4}:Er^{3+}$ at 10 K. The photoluminescence spectra of $CdGaInS_{4}:Er^{3+}$ measured in the wavelength ranges of 500 nm~900 nm and 1500~1600 nm at 10 K. Eight sharp emission peaks due to $Er^{3+}$ ion are observed in the regions of 549.5~560.0nm. 661.3~676.5nm. 811.1~ 834.1 nm and 1528.2~1556.0 nm in $CdGaInS_{4}:Er^{3+}$ single crystal. These PL peaks were attributed to the radiative transitions between the split electron energy levels of the $Er^{3+}$ ions occupied at $C_{2v}$ symmetry of the $CdGaInS_4$ single crystals host lattice.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.12
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• pp.38-43
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• 1994

GaAs and AlGaAs layers were grown by Molecular Beam Epitaxy (MBE) to fabricate hith performance GaAs MESFETs. Optimum growth temperatures were found to be 600$^{\circ}C$ from their Hall measurement data. MESFETs with the gate legth of 1${\mu}$m and the gate width of 100.mu.m were fabricated on the MBE-grown GaAs layters which has i-GaAs buffer layer and characterized. Knee volgate and mazimum transconductance of the devices were 1V, 224mS/mm, respectively. Cut-off frequency at on-wafer measuring pattern was measured to be 18 GHz. The MESFET with the 1${\mu}$m -thick i-Al$_{0.3}Ga_{0.7}$As buffer layer between nactive and i-GaAs was fabricated on order to reduce the leakage current which flows through the i-GaAs buffer layer. Its output resistance was 2.26 k${\Omega}$.mm which increased by a factor of 15 compared with the MESFET without i-Al$_{0.3}Ga_{0.7}$As buffer layer.

• Korean Journal of Clinical Laboratory Science
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• v.56 no.1
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• pp.43-51
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• 2024

[⁶⁸Ga]Ga-FAPI-04 is a promising radiopharmaceutical that binds specifically to fibroblast activation protein, which is overexpressed in more than 90% of malignant epithelial tumors but not in normal healthy tissue. This study aimed to develop an efficient method for producing ⁶⁸Ga-labelled FAPI-04 using a cassette-based automated synthesizer. [⁶⁸Ga]GaCl₃ was eluted from an Eckert & Ziegler Medical germanium-68/gallium-68 generator using 2.5 mL of 0.1 M HCl. The synthesis of the [⁶⁸Ga]Ga-FAPI-04 was performed using different concentrations of HEPES (1~2.5 M; 4-(2-hydroxyethyl) piperazine-1-ethanesulfonic acid) in 3~10 minutes; amounts of FAPI-04 precursor (5~50 ㎍) and reaction temperature (25℃~100℃) were optimized on the BIKBox^® synthesizer. The labeling efficiency of [⁶⁸Ga]Ga-FAPI-04 was greater than 96% (decay corrected) using 25 ㎍ FAPI-04 synthesized in 10 minutes at 100℃ in 2 M HEPES (pH 3.85), and its stability was greater than 99% at 6 hours. The total synthesis time of [⁶⁸Ga]Ga-FAPI-04 was 32.4 minutes, and the product met all quality control criteria. In this study, we developed and optimized a labeling method using [⁶⁸Ga]Ga-FAPI-04 using a cassette-based synthesizer. The devised method is expected to be useful for supplying [⁶⁸Ga]Ga-FAPI-04 for diagnosis in clinical practice.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.1-5
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• 2009

In this study, we performed growth of InGaN/GaN multi quantum well (MQW) structures on semi-polar (1-10]) GaN facet on 8-degree off oriented stripe patterned (100) Si substratcs by MOVPE. The structural and optical properties of the InGaN/GaN multi quantum well (MQW) structures grown on (1-101) GaN stripe depend on $NH_3$ flow rate, TMI flow rate and growth temperature are characterized by cathodoluminescence (CL) and scanning electron microscopy (SEM). With the decrease of $NH_3$ flow rate, the threading dislocation of (1-101) GaN is considerably reduced. We could control the transition wavelength of InGaN/GaN MQW structures from 391.5 nm to 541.2 nm depend on the growth conditions.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.494-499
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• 2004

The structural, electrical and optical properties of GaN epilayers grown on various ion-implanted sapphire(0001) substrates by MOCVD were investigated. Sapphire substrates have been widely adopted to grow high quality GaN epilayer despite the large differences of lattice constant and thermal expansion coefficient between them. So, GaN or AlN buffer layer and pre-treatment was indispensably introduced before the GaN epilayer growth. The ion-implanted substrate's surface had decreased internal free energies during the growth of the ions implanted sapphire(0001) substrates. The crystal and optical properties of GaN epilayers grown in ions implanted sapphire(0001) substrate were improved. Also, excessively roughened and modified surface by ions degraded the GaN epilyers. Not only the ionic radius but also the chemical species of implanted sapphire(0001) substrates could improve the properties of GaN epilayers grown by MOCVD. This result implies that higher quality of GaN epilayers was achieved by using ion-implanted sapphire(0001) substrate with various ions.

• Korean Journal of Materials Research
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• v.13 no.10
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.504-504
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• 2012

Gas 종류에 따른 플라즈마 제트 장치의 방전 특성을 조사하였다. 고전압 전극으로 내경 0.26 mm, 외경 0.52 mm인 의료용 바늘을 사용하였으며 바늘을 유리관 내부에 삽입하여 4가지 gas를 주입시킨다. Gas의 종류는 Ar, He, Ne, 그리고 $N_2$이다. Ar과 He의 방전 개시 전압은 각 1.2 kV, 1.0 kV이고 보라색 플라즈마가 방출된다. Ne 방전은 방전 개시 전압 시작 시점인 0.3 kV부터 유리관 밖으로 길게 방출 되며 주황색 플라즈마가 방출된다. 특히, Ne gas는 전기적 쇼크가 전혀 없다. $N_2$ gas는 방전개시전압이 2.0 kV로 가장 어려우며 유리관 밖으로 플라즈마 방출되지 않는다. 각 gas 별 스펙트럼의 특성도 파악하여 어떤 gas가 인체 및 생체에 적합한지 파악한다.

• 전기의세계
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• v.27 no.3
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• pp.3-6
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• 1978

SF$_{6}$gas는 고정압 게통의 모든 분야에 광범위하게 사용되여 차단기의 소호재료로써 또는 초초고압용의 cable 및 변압기등의 절연재료로써 많이 사용되어지고 있다. 이러한 모든 분야에서 보여주는 SF$_{6}$gas의 우수한 절연특성은 이 Gas의 사용범위를 더욱 확대시켜 줄 것이라고 생각된다. 그러나 이러한 높은 절연강도도 고기압하에서는 기대되어지는 절연강도 보다 훨씬 낮아지는 경향이 있으며 이러한 경향은 사용압력이 높아질수록 현저하다. 그러나 고전압용 전기기기의 절연재료로써 고기압의 SF$_{6}$gas가 점차적으로 많이 사용되고 있기 때문에 이 고기압 SF$_{6}$에 관한 연구 결과중 우선 여기서는 평등전계에서 전극표면상태 및 면적등에 의한 영향과 절연파괴 직전의 전류펄스에 대한 것을 저기압 SF$_{6}$gas에 관한 결과와 함께 기술하고자 한다.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.11
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• pp.117-126
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• 2003

GA(genetic algorithm) has a powerful searching ability and is comparatively easy to use and to apply as well. By that reason, GA is in the spotlight these days as an optimization skill for mechanical systems.$^1$However, GA has a low efficiency caused by a huge amount of repetitive computation and an inefficiency that GA meanders near the optimum. It also can be shown a phenomenon such as genetic drifting which converges to a wrong solution.$^{8}$ These defects are the reasons why GA is not widdy applied to real world problems. However, the low efficiency problem and the meandering problem of GA can be overcomed by introducing parallel computation$^{7}$ and gray code$^4$, respectively. Standard GA(SGA)$^{9}$ works fine on small to medium scale problems. However, SGA done not work well for large-scale problems. Large-scale problems with more than 500-bit of sere's have never been tested and published in papers. In the result of using the SGA, the powerful searching ability of SGA doesn't have no effect on optimizing the problem that has 96 design valuables and 1536 bits of gene's length. So it converges to a solution which is not considered as a global optimum. Therefore, this study proposes ExpGA(experience GA) which is a new genetic algorithm made by applying a new probability parameter called by the experience value. Furthermore, this study finds the solution throughout the whole field searching, with applying ExpGA which is a optimization technique for the structure having genetic drifting by the standard GA and not making a optimization close to the best fitted value. In addition to them, this study also makes a research about the possibility of GA as a optimization technique of large-scale design variable problems.