• Title/Summary/Keyword: band-gap engineering

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Characterization of AlN Thin Films Grown by Pulsed Laser Deposition on Sapphire Substrate (사파이어 기판에 펄스 레이저 증착법으로 성장된 AlN 박막의 특성)

  • Jeong, Eun-Hee;Chung, Jun-Ki;Jung, Rae-Young;Kim, Sung-Jin;Park, Sang-Yeup
    • Journal of the Korean Ceramic Society
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    • v.50 no.6
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    • pp.551-556
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    • 2013
  • AlN films with c-axis orientation and thermal conductivity characteristics were deposited by using Pulsed Laser Deposition and the films were characterized by changing the deposition conditions. In particular, we investigated the optimal conditions for the application of a heat sinking plane AlN thin film. Epitaxial AlN films were deposited on sapphire ($c-Al_2O_3$) single crystals by pulsed laser deposition (PLD) with an AlN target. AlN films were deposited at a fixed pressure of $2{\times}10^{-5}$ Torr, while the substrate temperature was varied from 500 to $700^{\circ}C$. According to the experimental results of the growth temperature of the thin film, AlN thin films were confirmed with a highly c-axis orientation, maximum grain size, and high thermal conductivity at $650^{\circ}C$. The thermal conductivity of the AlN thin film was found to increase compared to bulk AlN near the band gap value of 6.2 eV.

Improved Electrical Characteristics of Symmetrical Tunneling Dielectrics Stacked with SiO2 and Si3N4 Layers by Annealing Processes for Non-volatile Memory Applications (비휘발성 메모리를 위한 SiO2와 Si3N4가 대칭적으로 적층된 터널링 절연막의 전기적 특성과 열처리를 통한 특성 개선효과)

  • Kim, Min-Soo;Jung, Myung-Ho;Kim, Kwan-Su;Park, Goon-Ho;Jung, Jong-Wan;Chung, Hong-Bay;Lee, Young-Hie;Cho, Won-Ju
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.22 no.5
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    • pp.386-389
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    • 2009
  • The electrical characteristics and annealing effects of tunneling dielectrics stacked with $SiO_2$ and $Si_{3}N_{4}$ were investigated. I-V characteristics of band gap engineered tunneling gate stacks consisted of $Si_{3}N_{4}/SiO_2/Si_{3}N_{4}$ (NON), $SiO_2/Si_{3}N_{4}/SiO_2$ (ONO) dielectrics were evaluated and compared with $SiO_2$ single layer using the MOS (metal-oxide-semiconductor) capacitor structure. The leakage currents of engineered tunneling barriers (ONO, NON stacks) are lower than that of the conventional $SiO_2$ single layer at low electrical field. Meanwhile, the engineered tunneling barriers have larger tunneling current at high electrical field. Furthermore, the increased tunneling current through engineered tunneling barriers related to high speed operation can be achieved by annealing processes.

The Characteristics of Silicon Nitride Films Grown at Low Temperature for Flexible Display (플렉서블 디스플레이의 적용을 위한 저온 실리콘 질화물 박막성장의 특성 연구)

  • Lim, Nomin;Kim, Moonkeun;Kwon, Kwang-Ho;Kim, Jong-Kwan
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.26 no.11
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    • pp.816-820
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    • 2013
  • We investigated the characteristics of the silicon oxy-nitride and nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) at the low temperature with a varying $NH_3/N_2O$ mixing ratio and a fixed $SiH_4$ flow rate. The deposition temperature was held at $150^{\circ}C$ which was the temperature compatible with the plastic substrate. The composition and bonding structure of the nitride films were investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Nitrogen richness was confirmed with increasing optical band gap and increasing dielectric constant with the higher $NH_3$ fraction. The leakage current density of the nitride films with a high NH3 fraction decreased from $8{\times}10^{-9}$ to $9{\times}10^{-11}(A/cm^2$ at 1.5 MV/cm). This results showed that the films had improved electrical properties and could be acceptable as a gate insulator for thin film transistors by deposited with variable $NH_3/N_2O$ mixing ratio.

Synthesis and Characterization of MoS2/Graphene-TiO2 Ternary Photocatalysts for High-Efficiency Hydrogen Production under Visible Light

  • Zhang, Feng-Jun;Kong, Cui;Li, Xuan;Sun, Xian-Yang;Xie, Wen-Jie;Oh, Won-Chun
    • Journal of the Korean Ceramic Society
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    • v.56 no.3
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    • pp.284-290
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    • 2019
  • Ternary MoS2/graphene (G)-TiO2 photocatalysts were prepared by a simple hydrothermal method. The morphology, phase structure, band gap, and catalytic properties of the prepared samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-vis spectrophotometry, and Brunauer-Emmett-Teller surface area measurement. The H2 production efficiency of the prepared catalysts was tested in methanol-water mixture under visible light. MoS2/G-TiO2 exhibited the highest activity for photocatalytic H2 production. For 5 wt.% and 1 wt.% MoS2 and graphene (5MT-1G), the production rate of H2 was as high as 1989 µmol-1h-1. The catalyst 5MT-1G showed H2 production activity that was ~ 11.3, 5.6, and 4.1 times higher than those of pure TiO2, 1GT, and 5MT, respectively. The unique structure and morphology of the MoS2/G-TiO2 photocatalyst contributed to its improved hydrogen production efficiency under visible light.

Growth and effect of thermal annealing for ZnIn2Se4 single crystalline thick film by hot wall epitaxy (Hot Wall Epitaxy (HWE)법에 의한 ZnIn2Se4 단결정 후막 성장과 열처리 효과)

  • Hong, Myung-Seuk;Hong, Kwang-Joon
    • Journal of Sensor Science and Technology
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    • v.17 no.6
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    • pp.437-446
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    • 2008
  • Single crystalline ${ZnIn_2}{Se_4}$ layers were grown on thoroughly etched semi-insulating GaAs (100) substrate at $400^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating ${ZnIn_2}{Se_4}$ source at $630^{\circ}C$. The crystalline structure of the single crystalline thick films was investigated by the photoluminescence (PL) and Double crystalline X-ray rocking curve (DCRC). The carrier density and mobility of ${ZnIn_2}{Se_4}$ single crystalline thick films measured from Hall effect by van der Pauw method are $9.41{\times}10^{16}cm^{-3}$ and $292cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ${ZnIn_2}{Se_4}$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)$=1.8622 eV-$(5.23{\times}10^{-4}eV/K)T^2$/(T+775.5 K). After the as-grown ${ZnIn_2}{Se_4}$ single crystalline thick films was annealed in Zn-, Se-, and In-atmospheres, the origin of point defects of ${ZnIn_2}{Se_4}$ single crystalline thick films has been investigated by the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_{Se}$, $Zn_{int}$, and $Se_{int}$ obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Se-atmosphere converted ${ZnIn_2}{Se_4}$ single crystalline thick films to an optical p-type. Also, we confirmed that In in ${ZnIn_2}{Se_4}$/GaAs did not form the native defects because In in ${ZnIn_2}{Se_4}$ single crystalline thick films existed in the form of stable bonds.

Characterization of EFG Si Solar Cells

  • Park, S.H.
    • Journal of Sensor Science and Technology
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    • v.5 no.5
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    • pp.1-10
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    • 1996
  • Solar cells made of the edge-defined film-fed growth Si are characterized using current-voltage, surface photovoltage, electron beam induced current, electron microprobe, scanning electron microscopy, and electron backscattering. The weak temperature dependence of the I-V curves in the EFG solar cells is due to a voltage variable shunt resistance giving higher diode ideality factors than the ideal one. The voltage variable shunt resistance is modeled by a modified recombination mechanism which includes carrier tunneling to distributed impurity energy states in the band gap within the space-charge region. The junction integrity and the substrate quality are characterized simultaneously by combining I-V and surface photovoltage (SPV) measurements. The diode ideality factors and the surface photovoltages characterize the junction integrity while the SPV diffusion lengths characterizes the substrate quality. Most of the measured samples show the voltage variable shunt resistance although how serious it is depends on the solar cell efficiency. The voltage variable shunt resistance is understood as one of the most important factors of the degradation of EFG solar cells.

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a-Si:H TFT Using Ferroelectrics as a Gate Insulator

  • Hur, Chang-Wu;Kung Sung;Jung-Soo, Youk;Sangook Moon;Kim, Jung-Tae
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2004.05a
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    • pp.53-56
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    • 2004
  • The a-Si:H TFT using ferroelectric of SrTi $O_3$as a gate insulator is fabricated on glass. Dielectric characteristics of ferroelectric are superior to $SiO_2$and S $i_3$ $N_4$. Ferroelctric increases on-current, decreases thresh old voltage of TFT and also improves breakdown characteristics. The a-SiN:H has optical band gap of 2.61 eV, refractive index of 1.8~2.0 and resistivity of 10$^{13}$ - 10$^{15}$ $\Omega$cm, respectively. Insulating characteristics of ferroelectrics are excellent because dielectric constant of ferroelectric is about 60~100 and breakdown strength is over 1MV/cm. TFT using ferroelectric has channel length of 8~20${\mu}{\textrm}{m}$ and channel width of 80~200${\mu}{\textrm}{m}$. And it shows that drain current is 3.4$mutextrm{A}$ at 20 gate voltage, $I_{on}$ / $I_{off}$ is a ratio of 10$^{5}$ - 10$^{8}$ and $V_{th}$ is 4~5 volts, respectively. In the case of TFT without ferroelectric, it indicates that the drain current is 1.5 $mutextrm{A}$ at 20 gate voltage and $V_{th}$ is 5~6 volts. With the improvement of the ferroelectric thin film properties, the performance of TFT using this ferroelectric has advanced as a gate insulator fabrication technology is realized.zed.d.

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Properties of SrSnO3:Tb3+ Green-Emitting Phosphor Thin Films Grown on Sapphire and Quartz Substrates (사파이어와 석영 기판 위에 성장된 SrSnO3:Tb3+ 녹색 형광체 박막의 특성)

  • Cho, Shinho
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.29 no.9
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    • pp.546-551
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    • 2016
  • $SrSnO_3:Tb^{3+}$ phosphor thin films were prepared on sapphire and quartz substrates in the growth temperature range of $100{\sim}400^{\circ}C$ by using the radio frequency magnetron sputtering deposition. The resulting $SrSnO_3:Tb^{3+}$ thin films were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet-visible-infrared spectrophotometer, and photoluminescence spectrometer. The results indicated that the morphology, optical transmittance, band gap energy, and luminescence intensity of the phosphor thin films significantly depended on the growth temperature. All the thin films, regardless of the type of substrate, showed an amorphous behavior. As for the thin films deposited on sapphire substrate, the maximum crystallite size was obtained at a growth temperature of $400^{\circ}C$ and the strongest emission was green at 544 nm arising from the $^5D_4{\rightarrow}^7F_5$ transition of Tb3+. The average optical transmittance for all the thin films grown on sapphire and quartz substrates was decreased as the growth temperature increased from 100 to $400^{\circ}C$. The results suggest that the optimum growth temperatures for depositing highly-luminescent $SrSnO_3:Tb^{3+}$ phosphor thin films on sapphire and quartz substrates are 400 and $300^{\circ}C$, respectively.

A Study on the Analysis of Electromagnetic Characteristics and Design of a Cylindrical Photonic Crystal Waveguide with a Low-Index Core (중심-동공을 갖는 원통형태 광결정 도파로의 전자장 특성 분석 및 설계 연구)

  • Kim, Jeong I.
    • Journal of the Korea Convergence Society
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    • v.12 no.2
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    • pp.29-34
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    • 2021
  • In this paper, a cylindrical photonic crystal waveguide with a low-index core is first proposed. The core can be filled with air, liquid, or arbitrary dielectric materials. Exact analyses for the electromagnetic field characteristics of guided modes, by using appropriate Bessel functions and applying the boundary conditions, are performed to find out the guiding characteristics of the proposed waveguide. For verification and usage in design and manufacturing process, the computer-calculation of the waveguide transmission characteristics is also performed by applying the rigorous full-vectorial finite difference method. Providing variations of the effective area for the fundamental mode of the designed waveguide with different numbers of cladding layers, ranging from 2.6056 ㎛2 to 5.9673 ㎛2 over the operation wavelength, generally as the core refractive index n1 is higher, the mode area becomes smaller and the result leads to more optimistic effect for nonlinear device applications.

Development of a Portable Detection System for Simultaneous Measurements of Neutrons and Gamma Rays (중성자선과 감마선 동시측정이 가능한 휴대용 계측시스템 개발에 관한 연구)

  • Kim, Hui-Gyeong;Hong, Yong-Ho;Jung, Young-Seok;Kim, Jae-Hyun;Park, Sooyeun
    • Journal of radiological science and technology
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    • v.43 no.6
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    • pp.481-487
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    • 2020
  • Radiation measurement technology has steadily improved and its usage is expanding in various industries such as nuclear medicine, security search, satellite, nondestructive testing, environmental industries and the domain of nuclear power plants (NPPs). Especially, the simultaneous measurements of gamma rays and neutrons can be even more critical for nuclear safety management of spent nuclear fuel and monitoring of the nuclear material. A semiconductor detector comprising cadmium, zinc, and tellurium (CZT) enables to detect gamma-rays due to the significant atomic weight of the elements via immediate neutron and gamma-ray detection. Semiconductor sensors might be used for nuclear safety management by monitoring nuclear materials and spent nuclear fuel with high spatial resolution as well as providing real-time measurements. We aim to introduce a portable nuclide-analysis device that enables the simultaneous measurements of neutrons and gamma rays using a CZT sensor. The detector has a high density and wide energy band gap, and thus exhibits highly sensitive physical characteristics and characteristics are required for performing neutron and gamma-ray detection. Portable nuclide-analysis device is used on NPP-decommissioning sites or the purpose of nuclear nonproliferation, it will rapidly detect the nuclear material and provide radioactive-material information. Eventually, portable nuclide-analysis device can reduce measurement time and economic costs by providing a basis for rational decision making.