• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.145-145
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• 2008

갈륨-질화물(GaN) 기반의 고속전자이동도 트랜지스터(high electron mobility transistor, HEMT)는 최근 마이크로파 또는 밀리미터파 등의 차세대 고주파용 전력소자로 각광받고 있다. AlGaN/GaN HEMT는 이종접합구조(heterostructure) 로부터 발생하는 이차원 전자가스(two-dimensional electron gas, 2DEG) 채널을 이용하여 높은 전자 이동도, 높은 항복전압 및 우수한 고출력 특성을 얻는 것이 가능하다. AlGaN/GaN HEMT에서 ohmic 전극 부분과 채널이 형성되는 부분과의 거리에 의한 저항의 성분을 줄이고 전자의 터널링의 확률을 증가시키기 위해서 recess된 구조가 많이 사용되고 있다. 그러나 이 구조에서는 recess된 소스와 드레인에 의해 AlGaN층의 제거로 AlGaN층의 두께에 영향을 미치며 그에 따라 채널에 생성되는 전자의 농도를 변화시키게 된다. 본 논문에서는 소스와 드레인의 Trench 구조를 제안하였다. ohmic 전극 부분과 채널간의 거리의 감소로 특성을 향상시켜서 recess 구조의 장점이 유지된다. 그리고 recess되는 소스와 드레인 영역에서 AlGaN층을 전체적으로 제거하는 것이 아니고 Trench 즉 일부분만 제거하면서 AlGaN층의 두께의 변화에 따른 문제점도 줄일 수 있다. 따라서 이러한 전극 부분을 Trench구조화 시킨 AlGaN/GaN HEMT의 DC특성을 $ATLAS^{TM}$를 이용하여 전산모사하고 최적화된 구조를 제안하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.337-337
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• 2010

갈륨-질화물 (GaN) 기반의 고 전자 이동도 트랜지스터 (High Electron Mobility Transistor, HEMT)는 GaN의 큰 밴드갭 (3.4~6.2 eV), 높은 항복전계 (Ec~3 MV/cm) 및 높은 전자 포화 속도 (saturation velocity $-107\;cm{\cdot}s-1$) 특성과 AlGaN/GaN 등과 같은 이종접합구조(Heterostructure )로부터 발생하는 높은 면밀도(Sheet Concentration)를 갖는 이차원 전자가스(Two-Dimensional Electron Gas, 2DEG) 채널로 인해 차세대 고출력/고전압 소자로서 각광받고 있다. 하지만 드레인 쪽의 게이트 에지부분에 집중되는 전계로 인한 애벌린치 할복현상(Breakdown)이 발생하는 문제점이 있다. 따라서 AlGaN/GaN HEMT의 항복전압 향상을 위한 방법으로 필드플레이트(Field-Plate) 구조가 많이 사용되고 있다. 본 논문에서는 2D 시뮬레이션을 통한 AlGaN/GaN HEMT의 필드플레이트 구조 최적화를 수행하였다. 이를 위해 ATLASTM 전산모사 프로그램을 이용하여 필드플레이트 길이, 절연체 증류 및 두께에 따른 전류 전압 특성 및 전계 분산효과에 대한 전산모사를 수행하여 그 결과를 비교, 분석 하였다, 이를 바탕으로 기존의 구조에 비해 약 300%이상 향상된 항복전압을 갖는 AlGaN/GaN HEMT의 최적화된 필드 플레이트 구조를 제안하였다.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.72-75
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• 2012

In our experiments, strain-free nanowires(NWs) were dispersed on to the substrate, followed by e-beam lithography(EBL) to fabricate single nanowire ultraviolet(UV) sensor devices. Focused-ion beam(FIB), micro-Raman spectroscopy and photoluminescence were employed to characterize the structural and optical properties of AlGaN/GaN NWs. Also, I-V characteristics were obtained under both dark condition and UV lamp to demonstrate AlGaN/GaN NW-based UV sensors. The conductance of a single AlGaN/GaN UV sensor was 9.0 ${\mu}S$(under dark condition) and 9.5 ${\mu}S$ (under UV lamp), respectively. The currents were enhanced by excess carriers under UV lamp. Fast saturation and decay time were demonstrated by the cycled processes between UV lamp and dark condition. Therefore, we believe that AlGaN/GaN NWs have a great potential for UV sensor applications.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1227_1228
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• 2009

본 논문에서는 순방향 특성의 열화 없이 항복전압 향상을 위해 플로팅게이트와 필드플레이트를 적용한 AlGaN/GaN HEMTs를 제작하였다. AlGaN/GaN HEMTs에서의 항복전압은 게이트의 하단의 전계분포와 관련이 있다. 제안된 AlGaN/GaN HEMTs의 경우 GaN 층의 공핍영역을 효과적으로 확장시킴으로써 게이트와 드레인 사이의 영역에서의 전계집중을 성공적으로 완화시켰다. 필드플레이트와 플로팅게이트가 모두 적용된 소자의 항복전압이 1106 V인 반면, 필드플레이트만 적용한 소자의 항복전압은 688 V, 플로팅게이트만 적용한 소자의 항복전압은 828 V로 측정되었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.89-90
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• 2009

Three kind of surface-leakage-test-patterns were fabricated and measured in order to investigate the surface leakage current of AlGaN/GaN heterostructures through etched GaN buffer surface and mesa wall. The pattern which contain the mesa wall has the largest surface leakage current among them. The leakage current due to the mesa wall is predominant source of the leakage current of AlGaN/GaN devices.

• Journal of Sensor Science and Technology
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• v.25 no.5
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• pp.320-325
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• 2016

In this paper, we propose an AlGaN/GaN-based extended-gate metal-insulator-semiconductor high electron mobility transistor (MISHEMT)-type biosensor for detecting streptavidin-biotin complexes. We measure the drain current of the fabricated sensor, which varies depending on the antibody-antigen reaction of streptavidin with biotin molecules. To confirm the immobilization of biotin polyethylene glycol (PEG) thiol, we analyze the Au surface of a GaN sample using X-ray photoelectron spectroscopy (XPS). The proposed biosensor shows higher sensitivity than Si-based extended-gate metal oxide semiconductor field effect transistor (MOSFET)-type biosensor. In addition, the proposed AlGaN/GaN-based extended-gate MISHEMT-type biosensor exhibits better long-term stability, compared to the conventional AlGaN/GaN-based MISHEMT-type biosensor.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.878-882
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• 1999

Structural properties of $Al_xGa_1-_xN$ epilayers grown on (0001) sapphire substrate by plasma induced molecular beam epitaxy are investigated in the range of AlN molar fraction from 0.16 to 0.76. The AlN molar fraction estimated by X-ray diffraction agrees well with that of Rutherford backscattering spectroscopy, showing a good linear relationship. The uniform Auger electron microscopy depth profile and linear dependence of average atomic concentration of all the constituents of AlGaN epilayers on AlN molar fraction imply that the epitaxial growth of $Al_xGa_1-_xN$ layers with variation of AlN molar fraction is well controlled without the compositional fluctuation in depth of the epilayer. It is observed by atomic force microscopy that the surface grain shape of $Al_xGa_1-_xN$ epilayer changes from roundish to coalesced one with increasing AlN molar fraction.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.3
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• pp.461-467
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• 2008

It was studied the effect of a pre-deposited ultrathin Al layer as part of a buffer layer for the growth of GaN. AlN buffer layers were deposited on a Si(111) substrate using an RF sputtering technique, followed by GaN using hydride vapor phase epitaxy (HVPE). Several atomic layers of Al were deposited prior to AlN sputtering and the samples were compared with the others grown without pre-deposition of Al. And it was also studied the influence of AlN buffer layer thickness on the growth of GaN. The peak wavelength of the photoluminescence (PL) was varied with increasing the thickness of the GaN and AlN layers. The optimum thickness of AlN on a Si(111) substrate with an ultrathin Al layer was about $260{\AA}$. Scanning electron microscope (SEM) images showed coalescent surface morphology and X-ray diffraction (XRD) showed a strongly oriented GaN(0002) peak.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.161-166
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• 2013

AlN buffer layers have been used for the growth of GaN layers on Si substrates. However, the doping of high concentration of carriers into AlN layers is still not easy, therefore it may cause the increase of series resistance when it is used for the electrical or optical devices. In this work, to improve such a problem, the growth of GaN layers on Si substrates were performed using metal buffer layers instead of AlN buffer layer. We tried combinations of Ti, Al, Cr and Au as metal buffer layers for the growth of GaN on Si substrates. Surface morphology was measured by optical microscope and scanning electron microscope (SEM), and optical properties and crystalline quality were measured by photoluminescence (PL) and X-ray diffractometer (XRD), respectively. Electrical resistances for both cases of AlN and metal buffer layer were compared by current-voltage (I-V) measurement.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.4
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• pp.478-483
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• 2014

We propose a new method which can extract the information about the electronic traps in the semi-insulating GaN buffer of AlGaN/GaN heterostructure field-effect transistors (HFETs) using a simple test structure. The proposed method has a merit in the easiness of fabricating the test structure. Moreover, the electric fields inside the test structure are very similar to those inside the actual transistor, so that we can extract the information of bulk traps which directly affect the current collapse behaviors of AlGaN/GaN HEFTs. By applying the proposed method to the GaN buffer structures with various unintentionally doped GaN channel thicknesses, we conclude that the incorporated carbon into the GaN back barrier layer is the dominant origin of the bulk trap which affects the current collapse behaviors of AlGaN/GaN HEFTs.