• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.492-498
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• 2003

In this paper, We analyze the optimum bias conditions of cascode coupled microwave mixer for maximum conversion gain mixer. Microwave self-oscillating mixer by two GaAs MESFET cascode coupled, to upper GaAs MESFET operating as a oscillator with high Q dielectric resonator and the lower GaAs MESFET operated as a mixer with low noise and high conversion characteristics. As a result of experiments, cascode coupled microwave self oscillating mixer according to optimun bias shows an 5.92 dBm oscillating power, -132.0dBc/Hz @ 100KHz at 5.15GHz and 3dB conversion loss.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.169-179
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• 1999

In this paper, a GaAs MESFET single-ended resistive mixer with high linearity and isolation is designed. The bias voltage of this mixer is applied only gate of GaAs MESFET to use the channel resistance. The LO is applied the gate and the RF is applied the drain through 7-pole hairpin bandpass filter to obtain the proper isolation thru LO-RF. The IF is extracted from the source with short circuit and lowpass filter. Using extracted equivalent circuits for LO and RF, conversion loss is calculated and compared with result of harmonic balance analysis. Measured conversion loss of this S-band down converter mixer is 8.2~10.5dB by considering the measured 3.0~3.4dB RF 7-pole hairpin bandpass filter loss and IP3in is 26.5dBm at Vg=-0.85~-1.0V in distortion performance.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.667-671
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• 1998

The photoluminescence (pL) characteristics of hydride vapor phase epiyaxy (HVPE) grown GaN films on $MgAl_{2}O_{4}$ substrate were investigated with several growth conditions. The GaN films on $MgAl_{2}O_{4}$ substrate is autodoped with Mg atoms which thermally out-diffused from substrate lead to a PL characteristics of impurity doped ones. The Mg-related emission band intensity decreased with growth temperature may due to the evaporation of Mg atoms at the GaN film surfaces. and it also decreased with GaN film thicknesses. We can estimate the diffusion coefficient of Mg atoms in GaN under the consideration of diffusion phenomena between two infinite solids lead to a value of D= 2$\times$$lO^{-10}\textrm{cm}^2/sec.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.168-171
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• 1988

The p-n homo junction diode of the III-V ternary alloy semiconductor $In_{1-x}Ga_xP$ : S grown by the temperature gradient solution (TGS) was fabricated by Zn-diffusion, and it's characteristics was investigated. The carrier concentration of $In_{1-x}Ga_xP$ doped with sulfur, 0.5 mol %, was $1{\times}10^{17}cm^{-3}$ and the mobility was varied with the composition. In the case that the diffusion time was constant as 30 minutes. The temperature dependence of diffusion coefficient was decreased from D= $4.2{\times}10^{-5}$ exp (-1.74/$k_{B}T$) to D= $2.5{\times}10^{-5}$ exp (-3.272/$k_{B}T$) with increasing of composition $\times$ from 0.43 to 0.98. The major peak of E.L spectrum was due to D-A pair recombination and the peak intensity was increased with the increasing of input current. And the E.L intensity was decreased with the increasing temperature, and shift to the long wavelength. The luminescence efficiencies measured at $5^{\circ}C$, atmosphere temperature, was decreased from $2.6{\times}10^{-4}$% to $9.49{\times}10^{-6}$ % with increasing of composition it from 0.39, direct transition region, to 0.98, indirect transition region.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.301-307
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• 2006

We have investigated optical properties of p-modulation doped In(Ga)As quantum dots (QDs) on InP substrate with a comparison with the undoped QDs. Photoluminscence (PL) intensity of doped QDs at 10 K was about 10 times weaker than that of undoped QD sample. The decay time of doped QD sample at its PL peak, obtained from the time-resolved PL (TR-PL) experiment at 10 K, was very fast compared to that of undoped sample. We interpret that this fast decay time of the doped QD sample comes from the addition of non-radiative recombination paths, which are originated from the doping-related defects.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.58-64
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• 2001

The initiation and propagation lives of fatigue crack were studied for spot weldments composed of cold rolled steel plates(SPC$\times$SPC) and galvanized steel plates(GA$\times$GA) using DC potential drop method(DCPDM). Through the various test results, it was known that the fatigue crack initiation and propagation behaviors in all specimens could be definitely detected by DCPDM. The fatigue crack initiation life( $N_{i}$) detected by DCPDM in SPC$\times$SPC and GA$\times$GA spot weldments increased as the welding current and the nugget diameter( $N_{d}$) increased. The fatigue crack propagation life($\Delta$ $N_{f-i}$) declined as the difference of $N_{i}$ and the fatigue fracture life( $N_{f}$) also increased according to the decrease of fatigue load, $\Delta$P and the increase of nugget diameter. In the same spot weldments, the increase of nugget diameter came to increase fatigue crack propagation life owing to a decrease of stress concentration in front of nugget, especially the increasing extent for GA$\times$GA spot weldment was very high. In the welding current 6kA, $N_{f}$ for GA$\times$GA spot weldment decreased more than that of SPC$\times$SPC specimen due to zinc layer coated in steel plate and undersized nugget diameter. On the other hand, in 8kA and 10kA, the GA$\times$GA spot weldment showed higher $N_{f}$ in spite of lower $N_{i}$, than that of SPC$\times$SPC specimen except 3,000N fatigue load.ue load. load.d.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.119-119
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• 1999

GaN-based 물질들은 blue와 UV 영역의 LED, LD와 같은 광소자가 상용화되었을 뿐만아니라 HBT, FET와 같은 전기소자로도 널리 응용될 시점이지만 아직까지 해결되지 않은 문제점들이 있다. 그 중에 하나가 바로 GaN의 격자상수와 일치하는 기판이 없어 발생하는 dislocation인데, 이를 해결하기 위한 방법으로 새로운 기판이나, buffer, 또는 새로운 성장방법(ELOG) 등을 시도하고 있으나 dislocation density는 아직 높은 (107~1010cm-2) 상태이다. 이에 본 연구에서는 dislocation을 줄이기 위한 방책으로 InxGa1-xN를 새로운 buffer층으로 사용하여 GaN 박막을 MBE 방법으로 성장하였다. InxGa1-xN를 선택한 이유는 GaN와의 격자상수차이가 In0.12Ga0.88N일 경우 거의 일치한다는 보고가 있으며, 특히 InGaN의 melting point는 GaN의 성장온도 보다는 약간 높기 때문에 GaN 박막을 성장할 때와 식힐 때의 InGaN 원자결합은 약하게 작용되며, 결국 이는 열적인 stress를 줄여주게 된다. 이와 같이 성장된 GaN 박막은 그 결정성을 XRD로 분석하였고, 표면과 계면을 SEM으로 관찰하였다. 그리고 그 광학적 특성을 저온 PL로서 조사하였다. 그 결과를 살펴보면 35$^{\circ}$ 근방에서 GaN(0002) peak가 나온 것으로 보아 wurtzite 구조가 성장됨을 XRD로부터 확인하였다. 그리고 저온 (12K) PL에서는 3.470eV의 D$^{\circ}$X peak뿐만 아니라 3.258eV에 해당하는 peak를 얻었는데, 이는 InxGa1-xN buffer layer의 vapour pressure가 높은 (<50$0^{\circ}C$)에 도달하게 됨으로써 dissociation이 일어나면서 초기 성장이 이루어졌고 이는 다시 계면에서의 inter-diffusion을 발생시킨 것으로 보여진다.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1632-1636
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• 2013

$Ga_2O_3$ one-dimensional (1D) nanostructures were synthesized by using a thermal evaporation technique. The morphology, crystal structure, and sensing properties of the $Ga_2O_3$ nanostructures functionalized with Pt to $NO_2$ gas at room temperature under UV irradiation were examined. The diameters of the 1D nanostructures ranged from a few tens to a few hundreds of nanometers and the lengths ranged up to a few hundreds of micrometers. Pt nanoparticles with diameters of a few tens of nanometers were distributed around a $Ga_2O_3$ nanorod. The responses of the nanorods gas sensors fabricated from multiple networked $Ga_2O_3$ nanorods were improved 3-4 fold at $NO_2$ concentrations ranging from 1 to 5 ppm by Pt functionalization. The Pt-functionalized $Ga_2O_3$ nanorod gas sensors showed a remarkably enhanced response at room temperature under ultraviolet (UV) light illumination. In addition, the mechanisms via which the gas sensing properties of $Ga_2O_3$ nanorods are enhanced by Pt functionalization and UV irradiation are discussed.

• 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.

• Applied Microscopy
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• v.26 no.4
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• pp.479-487
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• 1996

Thin epilayer structures of GaAs/AlAs/InGaAs, grown by Molecular Beam Epitaxy, were investigated by high resolution transmission electron microscopy, Image in the [110] zone axis was taken and compared with the calculated images. The supercell structure which contains GaAs, AlAs and InGaAs layers was designed and was employed in the image calculation with MacTempas computer program. Good agreement was shown between experimental image and a set of calculated images with varying defocus and sample thickness.