• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.292-292
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• 2014

Wide band gap semiconductors, such as III-nitrides (GaN, AlN, InN, and their alloys), SiC, and diamond are expected to play an important role in the next-generation electronic devices. Specifically, GaN-based high electron mobility transistors (HEMTs) have been targeted for high power, high frequency, and high temperature operation electronic devices for mobile communication systems, radars, and power electronics because of their high critical breakdown fields, high saturation velocities, and high thermal conductivities. For the stable operation, high power, high frequency and high breakdown voltage and high current density, the fabrication methods have to be optimized with considerable attention. In this study, low ohmic contact resistance and smooth surface morphology to AlGaN/GaN on 2 inch c-plane sapphire substrate has been obtained with stepwise annealing at three different temperatures. The metallization was performed under deposition of a composite metal layer of Ti/Al/Ni/Au with thickness. After multi-layer metal stacking, rapid thermal annealing (RTA) process was applied with stepwise annealing temperature program profile. As results, we obtained a minimum specific contact resistance of $1.6{\times}10^{-7}{\Omega}cm2$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기물성,응용부문
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• pp.3-5
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• 2005

Ni/Au 쇼트키 접합의 산화를 통해 항복전압이 증가하고 누설 전류가 감소한 수평방향 GaN 쇼트키 장벽 다이오드를 제작하였다. 산화 과정 후, 턴-온 전압이 미세하게 증가하였으며 높은 애노드 전압하에서 애노드 전류가 증가하였다. 5분과 10분의 산화 과정 후, 누설 전류는 1nA 이하 수준으로 현저히 감소하였다. Edge Termination 방법으로 Floating Metal Ring을 사용하고, 산화 과정을 적용하여 제안된 GaN 쇼트키 장벽 다이오드의 항복전압은 750볼트의 큰 값을 얻을 수 있었다. 상온과 $125^{\circ}C$ 에서 제작한 GaN 쇼트키 장벽 다이오드의 역방향 회복 파형도 측정하였으며, 제작한 소자는 매우 빠른 역방향 회복 특성을 보였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권1호
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• pp.16-21
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• 2015

In this study, the effects of forming gas post metallization annealing (PMA) on recessed AlGaN/GaN-on-Si MOSHFET were investigated. The device employed an ICPCVD $SiO_2$ film as a gate oxide layer on which a Ni/Au gate was evaporated. The PMA process was carried out at $350^{\circ}C$ in forming gas ambient. It was found that the device instability was improved with significant reduction in interface trap density by forming gas PMA.

• 전기학회논문지
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• 제66권9호
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• pp.1351-1358
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• 2017

In this work, we investigated radiation hardness of GaN-based transistors which are strong candidates for next-generation power electronics. Field effect transistors with three types of gate structures including metal Schottky gate, recessed gate, and p-AlGaN layer gate were fabricated on AlGaN/GaN heterostructure on Si substrate. The devices were irradiated with energetic protons and alpha-particles. The irradiated transistors exhibited the reduction of on-current and the shift of threshold voltage which were attributed to displacement damage by incident energetic particles at high fluence. However, FET operation was still maintained and leakage characteristics were not degraded, suggesting that GaN-based FETs possess high potential for radiation-hardened electronics.

• KIEE International Transactions on Electrophysics and Applications
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• 제5C권2호
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• pp.54-57
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• 2005

Photoreflectance (PR) has been measured to investigate the characterization of the Si$_{3}$N$_{4}$Al$_{0.21}$ Ga$_{0.79}$As/GaAs and Al$_{0.21}$Ga$_{0.79}$As/GaAs heterostructures. In the PR spectrum, the caplayer thickness was 170 nm and Si$_{3}$N$_{4}$ was utilized as the capping material. The C peak is confirmed as the carbon defect with residual impurity originating from the growth process. After annealing, in the presence of the Si$_{2}$N$_{4}$ cap layer, band gap energy was low shifted. This result indicates that the Si$_{3}$N$_{4}$ cap layer controlled evaporation of the As atom.

• 한국전기전자재료학회논문지
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• 제15권7호
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• pp.591-596
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• 2002

In this work, epitaxial GaN is grown on sapphire substrate in AlGaN/GaN heterostructures. Deliberate oxygen doping of GaN grown by MOVPE has been studied. The electron concentration increased as a function of the square root of the oxygen partial Pressure. Oxygen is a shallow donor with a thermal ionization energy of $27\pm2 meV$ measured by temperature dependent Hall effects. A compensation ratio of $\theta$=0.3~0.4 was determined from Hall effect measurements. The formation energy of $O_N$ of $E^F$ =1.3eV determined from the experimental data, is lower than the theoretically predicted vague.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.151-151
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• 2008

갈륨-질화물(GaN) 기반의 고속전자이동도 트랜지스터(high electron mobility transistor, HEMT)는 마이크로파 또는 밀리미터파 등과 같은 고주파 대역의 통신시스템에 널리 사용되는 전자소자로 각광받고 있다. GaN HEMT는 AlGaN/GaN 또는 AlGaN/InGaN/GaN 등과 같은 이종접합구조(heterostructure)로부터 발생하는 이차원 전자가스(two-dimensional electron gas, 2DEG) 채널을 이용하여 캐리어 구속효과(carrier confinement) 및 이동도의 향상이 가능하다. 또한 높은 2DEG 채널의 면밀도(sheet concentration) 와 전자의 포화 속도(saturation velocity)를 바탕으로 고출력 동작이 가능하여 차세대 이동통신용 전력 증폭기로 주목받고 있다. 그러나 이론적으로 우수한 특성과 달리, 실제 소자에서는 epi 성장시의 결함이나 전위, 표면 상태에 따른 2DEG 감소 등의 영향으로 이론보다 높은 누설 전류와 낮은 항복 전압 특성을 가진다. 특히, 기존의 GaN HEMT 구조에서는 Drain-Side Gate Edge에서의 전계 집중이 항복 전압 특성에 미치는 영향이 크다. 본 논문에서는 이러한 문제를 해결하기 위해 Trapezoidal Gate구조를 이용하여 Drain 방향의 Gate Edge가 완만히 변하는 구조를 제안하였다. 이를 위해 $ATLAS^{TM}$ 전산모사 프로그램을 이용하여 Trapezoidal Gate 구조를 구현하여 형태에 따른 전류-전압 특성 및 소자의 스위칭 특성 및 Gate 아래 채널층에 형성되는 Electric Field의 분산을 조사하고, 이를 바탕으로 고속 동작 및 높은 항복 전압을 갖는 AlGaN/GaN HEMT의 최적화된 구조를 제안하였다. 새로운 구조의 Gate를 적용한 AlGaN/GaN HEMT는 Gate edge에서의 전계를 분산시켜 피크 값이 감소되는 것을 확인하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제5권2호
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• pp.107-112
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• 2005

We present an AlGaN/GaN metal-insulator-semiconductor-heterostructure field effect transistor (MIS-HFET) with an $Al_2O_3-HfO_2$ laminated high-k dielectric, deposited by plasma enhanced atomic layer deposition (PEALD). Based on capacitance-voltage measurements, the dielectric constant of the deposited $Al_2O_3-HfO_2$ laminated layer was estimated to be as high as 15. The fabricated MIS-HFET with a gate length of 102 m exhibited a maximum drain current of 500 mA/mm and maximum tr-ansconductance of 125 mS/mm. The gate leakage current was at least 4 orders of magnitude lower than that of the reference HFET. The pulsed current-voltage curve revealed that the $Al_2O_3-HfO_2$ laminated dielectric effectively passivated the surface of the device.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권5호
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• 한국결정성장학회지
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• 제22권1호
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• pp.11-14
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• 2012

AlGaN는 3.4~6.2 eV까지 넓은 밴드갭을 가지는 직접천이형 반도체이다. 최근에 자외영역의 광소자가 다양하게 응용되면서 자외선 발광이 가능한 AlGaN 역시 주목받고 있다. 이를 위해서는 고품질의 AlGaN 층이 필요하지만 GaN 층위에 AlGaN 층을 성장하는 것은 이들의 격자상수와 열팽창계수 차이로 인해 어렵다. 본 논문에서, multi-sliding boat법이 적용된 혼합소스 HVPE법을 이용하여 GaN template 위에 LED 구조를 성장하였다. 활성층의 Al 조성을 조절함으로써 AlGaN의 격자상수 변화와 광학적 변화를 관찰하고자 하였다. 에피 성장을 위해 HCl과 $NH_3$ 가스를 혼합소스 표면으로 흘려주었고, 수송가스로는 $N_2$를 사용하였다. 소스영역과 성장영역의 온도는 각각 900과 $1090^{\circ}C$로 안정화하였다. 성장 후 샘플은 x-ray diffraction(XRD)과 electro luminescence(EL) 측정을 하였다.