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김우병,Dong Keun Lee,류상욱 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.2
The a-IGZO deposited by using the rf sputtering method features a conductive or an insulatorcharacteristic based on amount of oxygen. We demonstrated that a post-treatment affects theresistance patterns of particular-sized InGaZnO(IGZO) thin films in a-IGZO thin-film transistors(TFTs). Post-annealing shifted the driving voltage of a-IGZO TFT to positive or negative values,depending on the annealing temperatures. Post-annealing may introduce oxygen vacancies or desorbedoxygen in the IGZO thin film. The changed driving voltage of IGZO TFTs coincides withthe shift of the resistance pattern of IGZO. The fabricated a-IGZO TFTs exhibited a field effectmobility of 6.2 cm2/Vs, an excellent subthreshold gate swing of 0.32 V/decade, and a high Ion/offratio of > 109. Under positive bias illumination stress (PBIS) and negative bias illumination stress(NBIS), after 3,600 seconds, the device threshold voltage shifted about 0.2 V and 0.3 V, respectively.
김우병 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.7
A low-cost and simple recycling process of waste thermoelectric modules has been investigated using chemical reduction methods. The recycling is separated by two processes, such as dissolving and reduction. When the waste thermoelectric chips are immersed into a high concentration of HNO3 aqueous solution at 100 oC, oxide powders, e.g., TeO2 and Sb2O3, are precipitated in the Bi3+ and HTeO2 + ions contained solution. By employing a reduction process with the ions contained solutions, Bi2Te3 nanoparticles are successfully synthesized. Due to high reduction potential of HTeO2 + to Te, Te elements are initially formed and subsequently Bi2Te3 nanoparticles are formed. The average particle size of Bi2Te3 was calculated to be 25 nm with homogeneous size distribution. On the other hand, when the precipitated powders reduced by hydrazine, Sb2O3 and Te nanoparticles are synthesized because of higher reduction potentials of TeO2 to Te. After the washing step, the Sb2O3 are clearly removed, results in Te nanoparticles.
질산산화법을 이용한 SiO<sub>2</sub>/Si 구조의 계면결함 제거
최재영,김도연,김우병,Choi, Jaeyoung,Kim, Doyeon,Kim, Woo-Byoung 한국재료학회 2018 한국재료학회지 Vol.28 No.2
5 nm-thick $SiO_2$ layers formed by plasma-enhanced chemical vapor deposition (PECVD) are densified to improve the electrical and interface properties by using nitric acid oxidation of Si (NAOS) method at a low temperature of $121^{\circ}C$. The physical and electrical properties are clearly investigated according to NAOS times and post-metallization annealing (PMA) at $250^{\circ}C$ for 10 min in 5 vol% hydrogen atmosphere. The leakage current density is significantly decreased about three orders of magnitude from $3.110{\times}10^{-5}A/cm^2$ after NAOS 5 hours with PMA treatment, although the $SiO_2$ layers are not changed. These dramatically decreases of leakage current density are resulted from improvement of the interface properties. Concentration of suboxide species ($Si^{1+}$, $Si^{2+}$ and $Si^{3+}$) in $SiO_x$ transition layers as well as the interface state density ($D_{it}$) in $SiO_2/Si$ interface region are critically decreased about 1/3 and one order of magnitude, respectively. The decrease in leakage current density is attributed to improvement of interface properties though chemical method of NAOS with PMA treatment which can perform the oxidation and remove the OH species and dangling bond.
광화학적 방법을 통한 InP계 양자점 표면결함 부동태화 연구
김도연,박현수,조혜미,김범성,김우병,Kim, Doyeon,Park, Hyun-Su,Cho, Hye Mi,Kim, Bum-Sung,Kim, Woo-Byoung 한국분말야금학회 2017 한국분말재료학회지 (KPMI) Vol.24 No.6
In this study, the surface passivation process for InP-based quantum dots (QDs) is investigated. Surface coating is performed with poly(methylmethacrylate) (PMMA) and thioglycolic acid. The quantum yield (QY) of a PMMA-coated sample slightly increases by approximately 1.3% relative to that of the as-synthesized InP/ZnS QDs. The QYs of the uncoated and PMMA-coated samples drastically decrease after 16 days because of the high defect state density of the InP-based QDs. PMMA does not have a significant effect on the defect passivation. Thioglycolic acid is investigated in this study for the effective surface passivation of InP-based QDs. Surface passivation with thioglycolic acid is more effective than that with the PMMA coating, and the QY increases from 1.7% to 11.3%. ZnS formed on the surface of the InP QDs and S in thioglycolic acid show strong bonding property. Additionally, the QY is further increased up to 21.0% by the photochemical reaction. Electron-hole pairs are formed by light irradiation and lead to strong bonding between the inorganic and thioglycolic acid sulfur. The surface of the InP core QDs, which does not emit light, is passivated by the irradiated light and emits green light after the photochemical reaction.
양자점 입도제어를 통한 양자점 감응형 태양전지 단락전류 향상
지승환,윤혜원,이진호,김범성,김우병 한국재료학회 2021 한국재료학회지 Vol.31 No.1
In this study, quantum dot-sensitized solar cells (QDSSC) using CdSe/ZnS quantum dots (QD) of various sizes with green, yellow, and red colors are developed. Quantum dots, depending their different sizes, have advantages of absorbing light of various wavelengths. This absorption of light of various wavelengths increases the photocurrent production of solar cells. The absorption and emission peaks and excellent photochemical properties of the synthesized quantum dots are confirmed through UV-visible and photoluminescence (PL) analysis. In TEM analysis, the average sizes of individual green, yellow, and red quantum dots are shown to be 5 nm, 6 nm, and 8 nm. The J-V curves of QDSSC for one type of QD show a current density of 1.7 mA/cm2 and an open-circuit voltage of 0.49 V, while QDSSC using three type of QDs shows improved electrical characteristics of 5.52 mA/cm2 and 0.52 V. As a result, the photoelectric conversion efficiency of QDSSC using one type of QD is as low as 0.53 %, but QDSSC using three type of QDs has a measured efficiency of 1.4 %.
과산화 티타늄 복합체를 이용한 염료감응형 태양전지용 페이스트의 제조 및 열처리 온도에 따른 특성
박현수,주소영,최준필,김우병,Park, Hyunsu,Joo, Soyeong,Choi, Joon-Phil,Kim, Woo-Byoung 한국분말야금학회 2015 한국분말재료학회지 (KPMI) Vol.22 No.6
The organic binder-free paste for dye-sensitized solar cell (DSSC) has been investigated using peroxo titanium complex. The crystal structure of $TiO_2$ nanoparticles, morphology of $TiO_2$ film and electrical properties are analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectra (EIS), and solar simulator. The synthesized $TiO_2$ nanopowders by the peroxo titanium complex at 150, 300, $400^{\circ}C$, and $450^{\circ}C$ have anatase phase and average crystal sizes are calculated to be 4.2, 13.7, 16.9, and 20.9 nm, respectively. The DSSC prepared by the peroxo titanium complex binder have higher $V_{oc}$ and lower $J_{sc}$ values than that of the organic binder. It can be attributed to improvement of sintering properties of $TCO/TiO_2$ and $TiO_2/TiO_2$ interface and to formation of agglomerate by the nanoparticles. As a result, we have investigated the organic binder-free paste and 3.178% conversion efficiency of the DSSC at $450^{\circ}C$.