• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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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.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.124-124
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• 2010

Much interest has been focused on InGaN-based materials and their quantum structures due to their optoelectronics applications such as light emitting diode (LED) and photovoltaic devices, because of its high thermal conductivity, high optical efficiency, and direct wide band gap, in spite of their high density of threading dislocations. Build-in internal field-induced quantum-confined Stark effect in InGaN/GaN quantum well LED structures results in a spatial separation of electrons and holes, which leads to a reduction of radiative recombination rate. Therefore, many growth techniques have been developed by utilizing lateral over-growth mode or by inserting additional layers such as patterned layer and superlattices for reducing threading dislocations and internal fields. In this work, we investigated various characteristics of InGaN multiple quantum wells (MQWs) LED structures grown on selectively wet-etched porous (SWEP) GaN template layer and compared with those grown on non-porous GaN template layer over c-plane sapphire substrates. From the surface morphology measured by atomic force microscope, high resolution X-ray diffraction analysis, low temperature photoluminescence (PL) and PL excitation measurements, good structural and optical properties were observed on both LED structures. However, InGaN MQWs LED structures grown on SWEP GaN template layer show relatively low In composition, thin well width, and blue shift of PL spectra on MQW emission. These results were explained by rough surface of template layer, reduction of residual compressive stress, and less piezoelectric field on MQWs by utilizing SWEP GaN template layer. Better electrical properties were also observed for InGaN MQWs on SWEP GaN template layer, specially at reverse operating condition for I-V measurements.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.231-231
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• 2013

ZnO은 hexagonal wurtzite 구조를 갖는 직접 천이형 화합물 반도체로서, 상온에서 3.37 eV 정도의 wide band gap energy를 가지고 있으며, 60 meV의 큰 엑시톤 결합 에너지(exciton binding energy)를 갖는다. 또한 동종 기판이 존재하고 열, 화학적으로 안정한 상태이며 습식 식각이 가능한 장점으로 인해 각광받고 있다. 또한, ZnO 박막은 우수한 전기 전도성을 나타내며 광학적 투명도가 우수하기 때문에 투명전극으로 많이 이용되어 왔고, 태양 전지(solar cell), 가스 센서, 압전소자 등 많은 분야에서 사용되고 있다. 이와 같은 ZnO박막을 안정적인 쇼트키 다이오드 특성을 얻기 위해서는 쇼트키 배리어 장벽의 형성이 필수적이다. Mg을 ZnO에 첨가하여 MgZnO 박막을 형성할 경우, 금속의 일함수와 MgZnO의 전자친화력 차이가 증가하여 더 큰 쇼트키 장벽 형성이 가능하며, 금속의 일함수가 큰 물질을 사용해야 한다. 또한, 박막의 결함이 적은 박막을 형성해야 하는 에피탁셜 박막이 필요하다. SiC는 높은 포화 전자 드리프트 속도(${\sim}2.7{\times}107$ cm/s), 높은 절연 파괴전압(~3 MV/cm)과 높은 열전도율(~5.0W/cm) 특징을 가지고 있으며, MgZnO/Al2O3의 격자 불일치는 ~19%인 반면에 MgZnO/SiC의 격자 불일치는 ~6%를 가진다. 금속의 일함수가 큰 Ag 금속은 열처리가 될 경우 AgOx가 될 경우 더욱 안정적인 쇼트키 장벽을 형성될 수 있을 것으로 판단된다. 본 연구에서는 쇼트키 접합을 형성하기 위해 금속의 일함수가 큰 Ag 금속을 사용하였으며, Al2O3 기판과 6H-SiC 기판위에 MgZnO(30 at.%) 박막을 증착하였다. 증착 후에 Ag를 증착 한 뒤 급속 열처리를 하였다. 열처리된 MgZnO의 경우 열처리 하지않은 소자보다 약 $10^5$ 이상의 우수한 on/off 특성을 보였다.

• 한국재료학회지
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• 제25권3호
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• pp.138-143
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• 2015

Aluminum nitride, a compound semiconductor, has a Wurtzite structure; good material properties such as high thermal conductivity, great electric conductivity, high dielectric breakdown strength, a wide energy band gap (6.2eV), a fast elastic wave speed; and excellent in thermal and chemical stability. Furthermore, the thermal expansion coefficient of the aluminum nitride is similar to those of Si and GaAs. Due to these characteristics, aluminum nitride can be applied to electric packaging components, dielectric materials, SAW (surface acoustic wave) devices, and photoelectric devices. In this study, we surveyed the crystallization and preferred orientation of AlN thin films with an X-ray diffractometer. To fabricate the AlN thin film, we used the magnetron sputtering method with $N_2$, NH3 and Ar. According to an increase in the partial pressures of $N_2$ and $NH_3$, Al was nitrified and deposited onto a substrate in a molecular form. When AlN was fabricated with $N_2$, it showed a c-axis orientation and tended toward a high orientation with an increase in the temperature. On the other hand, when AlN was fabricated with $NH_3$, it showed a-axis orientation. This result is coincident with the proposed mechanism. We fabricated AlN thin films with an a-axis orientation by controlling the sputtering electric power, $NH_3$ pressure, deposition speed, and substrate temperature. According to the proposed mechanism, we also fabricated AlN thin films which demonstrated high a-axis and c-axis orientations.

• 공업화학
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• 제25권3호
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• pp.233-236
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• 2014

유기발광 다이오드(Organic light emitting diodes)는 차세대 평판디스플레이로 학문적으로나 산업적으로 많은 관심을 받고 있다. 그러나 고성능 유기발광 다이오드의 생산을 위해서는 극복해야 할 많은 과제들이 여전히 남아있다. 그중 청색발광물질은 자체의 넓은 밴드갭으로 인해 녹색과 적색 발광재료에 비해 낮은 효율을 보이고 있다. 그러므로 많은 사람들이 높은 효율을 가진 청색 발광물질을 개발하기 위해 많은 노력을 기울이고 있다. 따라서 본 논문에서는 유기발광 다이오드의 기본개념과 청색 발광물질의 개발에 대해 간략하게 소개하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.232-232
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• 2010

Recently light emitting diodes (LEDs) have been expected as the new generation light sources because of their advantages such as small size, long lifetime and energy-saving. GaN, as a wide band gap material, is widely used as a material of LEDs and GaN nanorods are the one of the most widely investigated nanostructure which has advantages for the light extraction of LEDs and increasing the active area by making the cylindrical core-shell structure. Lately GaN nanorods are fabricated by various techniques, such as selective area growth, vapor-liquid-solid (VLS) technique. But these techniques have some disadvantages. Selective area growth technique is too complicated and expensive to grow the rods. And in the case of VLS technique, GaN nanorods are not vertically aligned well and the metal catalyst may act as the impurity. So we just tried to grow the GaN nanorods on Si substrate without catalyst to get the vertically well aligned nanorods without impurity. First we deposited the AlN buffer layer on Si substrate which shows more vertical growth mode than sapphire substrate. After the buffer growth, we flew trimethylgallium (TMGa) as the III group source and ammonia as the V group source. And during the GaN growth, we kept the ammonia flow stable and periodically changed the flow rate of TMGa to change the growth mode of the nanorods. Finally, as the optimization, we changed the various growth conditions such as the growth temperature, the working pressure, V/III ratio and the doping level. And we are still in the process to reduce the diameter of the nanorods and to extend the length of the nanorods simultaneously. In this study, we focused on the shape changing of GaN nanorods with different growth conditions. So we confirmed the shape of the nanorods by scanning electron microscope (SEM) and carried out the Photoluminescence (PL) measurement and x-ray diffraction (XRD) to examine the crystal quality difference between samples. Detailed results will be discussed.

• 대한금속재료학회지
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• 제50권1호
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• pp.78-85
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• 2012

Aluminum nitride(AlN) is a compound (III-V group) of hexagonal system with a crystal structure. Its Wurzite phase is a very wide band gap semiconductor material. It has not only a high thermal conductivity, a high electrical resistance, a high electrical insulating constant, a high breakdown voltage and an excellent mechanical strength but also stable thermal and chemical characteristics. This study is on the preferred orientation characteristics of AlN thin films by reactive evaporation using $NH_3$. We have manufactured an AlN thin film and then have checked the crystal structure and the preferred orientation by using an X-ray diffractometer and have also observed the microstructure with TEM and AlN chemical structure with FT-IR. We can manufacture an excellent AlN thin film by reactive evaporation using $NH_3$ under 873 K of substrate temperature. The AlN thin film growth is dependent on Al supplying and $NH_3$ has been found to be effective as a source of $N_2$. However, the nuclear structure of AlN did not occur randomly around the substrate a particle of the a-axis orientation in fast growth speed becomes an earlier crystal structure and is shown to have an a-axis preferred orientation. Therefore, reactive evaporation using $NH_3$ is not affected by provided $H_2$ amount and this can be an easy a-axis orientation method.

• 전력전자학회논문지
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• 제26권5호
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• pp.325-333
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• 2021

A 3 kW grid-tied PV inverter with Gallium nitride high-electron mobility transistor (GaN HEMT) for domestic commercialization was developed using boost converter and full-bridge inverter with LCL filter topology. Recently, many GaN HEMTs are manufactured as surface mount packages because of their lower parasitic inductance characteristic than standard TO (transistor outline) packages. A surface mount packaged GaN HEMT releases heat through either top or bottom cooling method. IGOT60R070D1 is selected as a key power semiconductor because it has a top cooling method and fairly low thermal resistances from junction to ambient. Its characteristics allow the design of a 3 kW inverter without forced convection, thereby providing great advantages in terms of easy maintenance and high reliability. 1EDF5673K is selected as a gate driver because its driving current and negative voltage output characteristics are highly optimized for IGOT60R070D1. An LCL filter with passive damping resistor is applied to attenuate the switching frequency harmonics to the grid-tied operation. The designed LCL filter parameters are validated with PSIM simulation. A prototype of 3 kW PV inverter with GaN HEMT is constructed to verify the performance of the power conversion system. It achieved high power density of 614 W/L and peak power efficiency of 99% for the boost converter and inverter.

• 전기전자학회논문지
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• 제22권4호
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• pp.916-921
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• 2018

본 논문에서는 고전압, 고전류 동작을 위한 전력 MOSFET 소자에 대한 전기적 특성을 시뮬레이션을 통해 분석하였다. 소자의 정적 특성을 향상시키기 위해 기존의 Si대신 4H-SiC를 이용했다. 4H-SiC는 넓은 에너지 밴드 갭에 의한 높은 한계전계를 갖기 때문에 고전압, 고전류 동작에서 Si보다 유리한 특성을 갖는다. 4H-SiC를 사용한 기존 VDMOSFET 구조는 p-base 영역 모서리에 전계가 집중되는 현상으로 인해 항복 전압이 제한된다. 따라서 본 논문에서는 p-base 영역의 모서리에 곡률을 주어 전계의 집중을 완화시켜 항복 전압을 높이고, 정적 특성을 개선한 곡률 VDMOSFET 구조를 제안하였다. TCAD 시뮬레이션을 통해 기존 VDMOSFET과 곡률 VDMOSFET의 정적 특성을 비교, 분석 하였다. 곡률 VDMOSFET은 기존 구조에 비해 온저항의 증가 없이 68.6% 향상 된 항복 전압을 갖는다.

• Current Photovoltaic Research
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• 제7권1호
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• pp.9-14
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• 2019

Carrier selective solar cell structure has allured curiosity of photovoltaic researchers due to the use of wide band gap transition metal oxide (TMO). Distinctive p/n-type character, broad range of work functions (2 to 7 eV) and risk free fabrication of TMO has evolved new concept of heterojunction intrinsic thin layer (HIT) solar cell employing carrier selective layers such as $MoO_x$, $WO_x$, $V_2O_5$ and $TiO_2$ replacing the doped a-Si layers on either front side or back side. The p/n-doped hydrogenated amorphous silicon (a-Si:H) layers are deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD), which includes the flammable and toxic boron/phosphorous gas precursors. Due to this, carrier selective TMO is gaining popularity as analternative risk-free material in place of conventional a-Si:H. In this work hole selective materials such as $MoO_x$, $WO_x$ and $V_2O_5$has been investigated. Recently $MoO_x$, $WO_x$ & $V_2O_5$ hetero-structures showed conversion efficiency of 22.5%, 12.6% & 15.7% respectively at temperature below $200^{\circ}C$. In this work a concise review on few important aspects of the hole selective material solar cell such as historical developments, device structure, fabrication, factors effecting cell performance and dependency on temperature has been reported.