• Title/Summary/Keyword: bandgap

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Phase Modulation Efficiency of the Electrooptic Modulator using GaAs/AlGaAs (GaAs/AlGaAs을 이용한 전계광학 변조기의 위상변조 효율)

  • 최왕엽;박화선;이종창;변영태;김선호
    • Proceedings of the Optical Society of Korea Conference
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    • 2002.11a
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    • pp.192-193
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    • 2002
  • In this paper we investigate the phase modulation efficiency in the electrooptic phase modulator using PPpinNN GaAs/AlGaAs W-type waveguide. The phase change is affected by the refractive index change taking place inside the depletion region. The behavior of the modulator can be understood in terms of two electric field-related and two carrier-related effects linear electrooptic, quadratic electrooptic, plasma, and bandgap shift. As a result, the phase modulation efficiency was measured about 34.6($^{\circ}$/V$.$mm) for the TE polarized light. The quadratic electrooptic coefficient R 5.82${\times}$10$\^$-15/($\textrm{cm}^2$/V$^2$) is Obtained ant the Phase efficiency Caused by the quadratic electrooptic effect is about 10 times larger than that from the conventional linear electrooptic effect.

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Fabrication and Characterization of Hexagonal Tungsten Oxide Nanopowders for High Performance Gas Sensing Application (육방정계 텅스텐옥사이드 나노분말의 합성과 고성능 가스센서응용을 위한 성능 평가)

  • Park, Jinsoo
    • Journal of Powder Materials
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    • v.26 no.1
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    • pp.28-33
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    • 2019
  • The gas sensor is essential to monitoring dangerous gases in our environment. Metal oxide (MO) gas sensors are primarily utilized for flammable, toxic and organic gases and $O_3$ because of their high sensitivity, high response and high stability. Tungsten oxides ($WO_3$) have versatile applications, particularly for gas sensor applications because of the wide bandgap and stability of $WO_3$. Nanosize $WO_3$ are synthesized using the hydrothermal method. As-prepared $WO_3$ nanopowders are in the form of nanorods and nanorulers. The crystal structure is hexagonal tungsten bronze ($MxWO_3$, x =< 0.33), characterized as a tunnel structure that accommodates alkali ions and the phase stabilizer. A gas detection test reveals that $WO_3$ can detect acetone, butanol, ethanol, and gasoline. This is the first study to report this capability of $WO_3$.

SiC Motor Drive for Elevator System (엘리베이터 시스템을 위한 SiC 권상기 드라이브)

  • Gwon, Jin-Su;Moon, Seok-Hwan;Kim, Ju-Chan;Lee, Joon-Min
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.3
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    • pp.147-152
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    • 2019
  • With the recent emphasis on the importance of energy conservation, studies on high-efficiency elevator systems are being continuously conducted. Therefore, pulse width modulation converters are commonly used in traction drives on elevator systems. Wide bandgap devices have been increasingly commercialized, and their application to power conversion systems, such as renewable and energy storage system, has been gradually increasing. In this study, a SiC inverter for an elevator traction drive is investigated. In particular, an inverter is designed to minimize stray and parasitic inductance. Input and output filters are designed by considering switching frequency. The designed SiC inverter reduces volume by approximately 32% compared with that of a Si inverter, and power converter efficiency is over 98.8%.

Performance Analysis of Photonic Crystal Enhanced Micro-Combustor Thermophotovoltaic System for Drone Application (광결정 표면을 이용한 드론용 마이크로 연소기 열광전 에너지변환시스템의 성능해석)

  • Lee, Junghun
    • 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).

α-Fe2O3 nanostructure-based gas sensors

  • Lee, Seonyong;Jang, Ho Won
    • Journal of Sensor Science and Technology
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    • v.30 no.4
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    • pp.210-217
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    • 2021
  • Gas sensors based on semiconducting metal oxides have attracted considerable attention for various applications owing to their facile, cheap, and small-scale manufacturing processes. Hematite (α-Fe2O3) is widely considered as a promising candidate for a gas-sensing material owing to not only its abundance in the earth's crust and low price but also its chemical stability and suitable bandgap energy. However, only a few studies have been performed in this direction because of the low gas response and sluggish response of hematite-based gas sensors. Nanostructures present a representative solution to both overcome these disadvantages and exploit the desirable features to produce high-performance gas sensors. However, several challenges remain for adopting gas sensors based on metal oxide nanostructures, such as improving cost efficiency and facilitating mass production. This review summarizes the recent studies on gas sensors based on hematite nanostructures. It also provides useful insights into various strategies for enhancing the gas-sensing properties of gas sensors based on hematite nanostructures.

Above bandgap optical properties of ZnS grown by hot-wall epitaxy

  • Lee, M.S.;Koo, M.S.;Kim, T.J.;Kim, Y.D.;Yoo, Y.M.;O, B.;Choi, Y.D.
    • Journal of Korean Vacuum Science & Technology
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    • v.3 no.2
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    • pp.112-115
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    • 1999
  • The real ($\varepsilon$1) and imaginary ($\varepsilon$2) parts of the dielectric function of ZnS have been measured by spectroscopic ellipsometry (SE) in the 3.7-6.0 eV photon-energy range at room temperature. The obtained dielectric function spectra reveal distinct structures at energies E0/(E0+$\Delta$0) and E1 critical points. The spectrum after chemical treatment to remove surface oxide overlayer showed that these data seem to be the best representation of the dielectric function of ZnS, having the largest $\varepsilon$2 value at E1 peak region reported so far by SE. Dielectric-related optical constants of ZnS, such as the complex refractive indices (n+n=ik), absorption coefficient, and reflectance, are also presented.

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Temperature Effects on the Optical Properties of Doped Amorphous Silicon (도우핑된 비정질 실리콘의 온도에 따른 광학적 특성)

  • Park, Jin Seok;Han, Min-Koo;Lee, Chung Han
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.23 no.4
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    • pp.506-514
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    • 1986
  • Experimental results are reported concerning temperture effects from room temperature to 100\ulcorner on the optical properties of N-and P-type hydrogenated amorphous silicon films prepared by RF glow discharege. Optical absorption coefficient and optical bandgap have been measured and analyzed as a function of temperature. Optical absorption coefficient increase monotonically with temperature, while the optical bandgape of doped amorphous silicons decrease linearly by about 4-7x10**-4 [ev/k].

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Halide Perovskites for X-ray Detection: The Future of Diagnostic Imaging

  • Nam Joong Jeon;Jung Min Cho;Jung-Keun Lee
    • Progress in Medical Physics
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    • v.33 no.2
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    • pp.11-24
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    • 2022
  • X-ray detection has widely been applied in medical diagnostics, security screening, nondestructive testing in the industry, etc. Medical X-ray imaging procedures require digital flat detectors operating with low doses to reduce radiation health risks. Recently, metal halide perovskites (MHPs) have shown great potential in high-performance X-ray detection because of their attractive properties, such as strong X-ray absorption, high mobility-lifetime product, tunable bandgap, low-temperature fabrication, near-unity photoluminescence quantum yields, and fast photoresponse. In this paper, we review and introduce the development status of new perovskite X-ray detectors and imaging, which have emerged as a new promising high-sensitivity X-ray detection technology. We discuss the latest progress and future perspective of MHP-based X-ray detection in medical imaging. Finally, we compare the conventional detection methods with quantum-enhanced detection, pointing out the challenges and perspectives for future research directions toward perovskite-based X-ray applications.

Effect on the Thermal Treatment for Improving Efficiency in Silicon Heterojunction Solar Cells (이종접합 실리콘 태양전지의 효율 개선을 위한 열처리의 효과)

  • Hyeong Gi Park;Junsin Yi
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.37 no.4
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    • pp.439-444
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    • 2024
  • This study investigates the post-thermal treatment effects on the efficiency of silicon heterojunction solar cells, specifically examining the influence of annealing on p-type microcrystalline silicon oxide and ITO thin films. By assessing changes in carrier concentration, mobility, resistivity, transmittance, and optical bandgap, we identified conditions that optimize these properties. Results reveal that appropriate annealing significantly enhances the fill factor and current density, leading to a notable improvement in overall solar cell efficiency. This research advances our understanding of thermal processing in silicon-based photovoltaics and provides valuable insights into the optimization of production techniques to maximize the performance of solar cells.

Inductance-Enhanced Corrugated Ground Planes for Miniaturization and Common Mode Noise Suppression of Differential Line in High-Speed Packages and PCBs (고속 반도체 패키지 및 PCB 내 공통 모드 잡음 감쇠를 위한 소형화 된 인덕턴스 향상 파형 접지면 기반 차동 신호선)

  • Tae-Soo Park;Myunghoi Kim
    • Journal of Advanced Navigation Technology
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    • v.28 no.2
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    • pp.246-249
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    • 2024
  • In this paper, we present a miniaturized differential line (DL) using inductance-enhanced corrugated ground planes (LCGP) for effective common-mode (CM) noise suppression in high-speed packages and printed circuit boards. The LCGP-DL demonstrates the CM noise suppression in the frequency range from 2.09 GHz to 3.6 GHz. Furthermore, to achieve the same low cutoff frequency, the LCGP-DL accomplishes a remarkable 23.2% reduction in size compared to a reference DL.