• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.3
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• pp.309-316
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• 2021

In this paper, the electrical power output of the micro-combustor thermophotovoltiac(TPV) system was analyzed. The system consists of a micro-combustor, photonic crystals(PhCs), and photovoltaic cells(PV cells). The system has a micro-combustor that can achieve over 1,000 K surface temperature by consuming 2.5 g/h hydrogen fuel. Also, this system incorporates current state-of-the-art PhCs surfaces(2D Ta PhCs and Tandem Filter) to increase electrical power output. In addition, InGaAsSb PV cell, which bandgap is 0.55 eV, was applied to convert a wide range of radiative energy. The performance analysis shows that a single micro-combustor TPV system can produce 0.4 W ~ 27.7 W electrical power with the temperature change of emitter(900 K ~ 1,500 K) and PV cell(250 K ~ 400 K).

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.194.1-194.1
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• 2015

Transition metal dichalcogenide (TMD) with layered structure, has recently been considered as promising candidate for next-generation flexible electronic and optoelectronic devices because of its superior electrical, optical, and mechanical properties.[1] Scalability of thickness down to a monolayer and van der Waals expitaxial structure without surface dangling bonds (consequently, native oxides) make TMD-based thin film transistors (TFTs) that are immune to the short channel effect (SCE) and provide very high field effect mobility (${\sim}200cm^2/V-sec$ that is comparable to the universal mobility of Si), respectively.[2] In addition, an excellent photo-detector with a wide spectral range from ultraviolet (UV) to close infrared (IR) is achievable with using $WSe_2$, since its energy bandgap varies between 1.2 eV (bulk) and 1.8 eV (monolayer), depending on layer thickness.[3] However, one of the critical issues that hinders the successful integration of $WSe_2$ electronic and optoelectronic devices is the lack of a reliable and controllable doping method. Such a component is essential for inducing a shift in the Fermi level, which subsequently enables wide modulations of its electrical and optical properties. In this work, we demonstrate n-doping method for $WSe_2$ on poly-4-vinylphenol and poly (melamine-co-formaldehyde) (PVP/PMF) insulating layer and adjust the doping level of $WSe_2$ by controlling concentration of PMF in the PVP/PMF layer. We investigated the doping of $WSe_2$ by PVP/PMF layer in terms of electronic and optoelectronic devices using Raman spectroscopy, electrical measurements, and optical measurements.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.120-120
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• 2008

We demonstrate epitaxial growth of ZnO thin films on 4H-SiC(0001) substrates using pulsed laser deposition (PLD). ZnO and SiC have attracted attention for their special material properties as wide band gap semiconductors. Especially, ZnO could be applied to optoelectronic applications such as light emitting devices and photo detectors due to its direct wide bandgap (Eg) of ~3.37eV and large exciton binding energy of ~60meV. SiC shows a good lattice matching to ZnO compared with other commonly used substrates and in this regard SiC is a good candidate as a substrate for ZnO. In this work, ZnO thin films were grown on 4H-SiC(0001) substrates by PLD using an Nd:YAG laser with a 355nm wavelength. The crystalline properties of the films were evaluated by x-ray diffraction (XRD) $\theta-2\theta$, rocking curve and pole figure measurements using a high-resolution diffractometer. The surface morphology of the films was studied by atomic force microscopy (AFM).

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.63-70
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• 2023

Today, the importance of power semiconductors continues to increase due to serious environmental pollution and the importance of energy. Particularly, SiC-MOSFET, which is one of the wide bandgap (WBG) devices, has excellent high voltage characteristics and is very important. However, since the electrical properties of SiC-MOSFET are heatsensitive, thermal management through a package is necessary. In this paper, we propose an insulated metal substrate (IMS) method rather than a direct bonded copper (DBC) substrate method used in conventional power semiconductors. IMS is easier to process than DBC and has a high coefficient of thermal expansion (CTE), which is excellent in terms of cost and reliability. Although the thermal conductivity of the dielectric film, which is an insulating layer of IMS, is low, the low thermal conductivity can be sufficiently overcome by allowing a process to be very thin. Electric-thermal co-simulation was carried out in this study to confirm this, and DBC substrate and IMS were manufactured and experimented for verification.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.400-406
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• 2024

Next-generation wide-bandgap semiconductors such as SiC, GaN, and Ga2O3 are being considered as potential replacements for current silicon-based power devices due to their high mobility, larger size, and production of high-quality wafers at a moderate cost. In this study, we investigate the gradual modulation of chemical composition in multi-stacked metal oxide semiconductor thin films to enhance the performance and bias stability of thin-film transistors (TFTs). It demonstrates that adjusting the Ga ratio in the indium gallium oxide (IGO) semiconductor allows for precise control over the threshold voltage and enhances device stability. Moreover, employing multiple deposition techniques addresses the inherent limitations of solution-processed amorphous oxide semiconductor TFTs by mitigating porosity induced by solvent evaporation. It is anticipated that solution-processed indium gallium oxide (IGO) semiconductors, with a Ga ratio exceeding 50%, can be utilized in the production of oxide semiconductors with wide band gaps. These materials hold promise for power electronic applications necessitating high voltage and current capabilities.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.595-599
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• 2004

We investigated the structural, electrical and magnetic properties of Mn-doped $CuAlO_2$ delafossite ceramics ($CuAl_{1-x}Mn_{x}O_2,\;0\le\;x\;\le0.05$), synthesized by solid-state reaction method in an air atmosphere at a sintering temperature of $1150^{\circ}C$. The solubility limit of Mn ions in delafossite $CuAlO_2$ was found to be as low as about 3 $mol\%$. Positive Hall coefficient and the temperature dependence of conductivity established that non-doped $CuAlO_2$ ceramic is a variable-range hopping p-type semiconductor. It was found that the Mn-doping in $CuAlO_2$ rapidly reduced the hole concentration and conductivity, indicating compensation of free holes. The analysis of the magnetization data provided an evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Mn ions in $CuAl_{1-x}Mn_{x}O$ alloy, leading to an almost paramagnetic behavior in this alloy.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.89.2-89.2
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• 2010

The dye-sensitized solar cell (DSSC) is a device for the conversion of visible light into electricity, based on the sensitization of wide bandgap semiconductors. The performance of the cell mainly depends on a dye used as sensitizer. The absorption spectrum of the dye and the anchorage of the dye to the surface of $TiO_2$ are important parameters determining the efficiency of the cell. Generally, transition metal coordination compounds(ruthenium polypyridyl complexes) are used as the effective sensitizers, due to their intense charge-transfer absorption in the whole visible range and highly efficient metal-to ligand charge transfer. However, ruthenium polypyridyl complexes contain a heavy metal, which is undesirable from point of view of the environmental aspects. Moreover, the process to synthesize the complexes is complicated and costly. Alternatively, organic dyes can be used for the same purpose with an acceptable efficiency. The advantages of organic dyes include their availability and low cost. We designed and synthesized a series of organic sensitizers containing long wavelength absorption-chromophores for the dye sensitized solar cell. The DSSC composed of Blue-chromophores for the sensitization absorbed long wavelength region which is different also applied into the dye-cocktail (mixing) system. The photovoltaic property of DSSCs organic long wavelength absorption-chromophores were measured and evaluated by comparison with that of individual chromophores.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.113-113
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• 2009

This paper describes the characteristics of a poly 3C-SiC micro heater which was fabricated on $AlN(0.1{\mu}m)/3C-SiC(1.0{\mu}m)$ suspended membranes by surface micro- machining technology. The 3C-SiC and AlN thin films which have wide energy bandgap and very low lattice mismatch were used sensors for high temperature and voltage environments. The 3C-SiC thin film was used as micro heaters and temperature sensor materials simultaneously. The implemented 3C-SiC RTD (resistance of temperature detector) and the power consumption of micro heaters were measured and calculated. The TCR (thermal coefficient of the resistance) of 3C-SiC RTD is about -5200 $ppm/^{\circ}C$ within a temperature range from $25^{\circ}C$ to $50^{\circ}C$ and -1040 $ppm/^{\circ}C$ at $500^{\circ}C$. The micro heater generates the heat about $500^{\circ}C$ at 10.3 mW. Moreover, durability of 3C-SiC micro heaters in high voltages is better than pt micro heaters. A thermal distribution measured and simulated by IR thermovision and COMSOL is uniform on the membrane surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.266.2-266.2
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• 2016

최근 디스플레이 산업의 확대에 따라 투명 전도 산화물(Transparent Conducting Oxides:TCOs)의 수요가 급증하고 있다. 이 중 ZnO는 wide bandgap (3.37eV)와 large exciton binding energy (60meV)의 값을 가져 차세대 투명 전도 산화물, LED와 LD 등의 소자 소재로 각광받고 있다. ZnO는 electron을 내어놓는 native defect 때문에 기본적으로 n-type 물성을 띈다. 그래서 dopant를 이용해 p-type ZnO를 제작할 때 native defect를 줄이는 것이 중요한 요점이 된다. 이 때 buffer layer를 사용하여 native defect를 줄이는 방법이 사용되고 있다. 본연구에서는 RF-magnetron sputtering법을 이용하여 c-plane sapphire 기판 위에 다양한 조건의 ZnO buffer layer를 증착하고, 그 위에 ZnO:(Al,P) co-doping한 APZO를 증착하였다. ZnO buffer layer 증착조건의 변수는 증착온도와 Ar:O2의 비율을 변수로 두었다. 이러한 박막을 FE-SEM, XRD, Hall effect measurement, AFM을 통하여 미세구조와 물성을 관찰하였다. 이 때 APZO보다 낮은 증착온도에서 ZnO buffer layer가 증착되면 APZO를 증착하는 동안 chamber 내부에서 열처리하는 효과를 얻게 되고, UHV(Ultra High Vaccum)에서 열처리 될 때 ZnO buffer layer의 mophology와 결정성이 변하게 되는 모습을 관찰아혔다. 또한 본 실험을 통해 ZnO buffer layer의 증착 온도가 APZO의 증착온도보다 높을 때 제어 가능한 실험이 됨을 확인 할 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.182.1-182.1
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• 2015

Transparent conducting oxides (TCOs)는 높은 투과율과 낮은 전기전도도를 갖고 있어 광다이오드, 태양전지 등 광소자에 적용하기 위해 많은 연구가 진행되어 왔다. 특히 Indium oxide 계열의 박막은 TCO 물질 중 하나로서 3.6 eV 의 wide bandgap을 가지고 있고, 높은 투과율과 낮은 전기 전도도 (< $10-3{\Omega}cm$)를 보여 다양한 응용이 가능해 오랫동안 연구 되어 지고 있다. 게다가 Indium oxide 계열의 박막은 낮은 가격과 화학적 안정성, 공정과정의 편의성 등 다양한 이점을 가지고 있어서 현재는 더 낮은 가격으로 생성해 더 높은 효율을 만드는데 관심이 집중되고 있다. 이러한 박막은 태양광 흡수층에서 생성되는 캐리어의 이동 및 외부 전극과의 접촉에서 발생하는 손실을 줄이기 위한 전극용 소재로 연구되어지고 있다. 본 연구에서는 Indium Molybdenum Oxide 박막을 Indium oxide와 Molybdenum 타겟을 이용하여 co-sputtering 방법으로 증착하였다. Indium molybdenum oxide 박막은 일정한 Mo 도핑농도와 일정한 Ar 개스 분압에서 다양한 기판온도 변화를 통해 증착하였다. 제작된 Indium molybdenum oxide 박막은 Hall Effect Measurement, Ultraviolet-Visible spectroscopy 및 X-Ray Diffraction (XRD) 등을 분석해 기판의 온도변화에 따른 전기비저항 및 광 투과도의 특성변화를 조사하였다.