• Korean Journal of Metals and Materials
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• v.46 no.3
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• pp.169-173
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• 2008

Characteristics of etching and induced surface morphology variation by wet-etching of n-type GaN were investigated using phosphoric acidic solutions. Generally, the etch-rate was increased as the temperature of the etch solutions was increased, and the highest etch rate of about $300{\AA}/min$ was achieved at the temperature of $180^{\circ}C$. The morphology variation of the etched surface was observed by optical microscopy and atomic force microscopy. Initially, high density of hexagonal holes or pits were formed on the etched surface at the time of 40 min with the bimodal size of $20{\mu}m$ or $5{\mu}m$, respectively. However, as the etching time was increased further, the lateral size of the hexagonal holes or pits was increased, and finally, joined and merged together at the time of 100 min. This means that the etching of n-type GaN by phosphoric acidic solutions proceeded through the lateral widening and the merging of initial holes and pits.

• Korean Journal of Materials Research
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• v.32 no.10
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• pp.425-428
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• 2022

In this study, Y₃Al₅O₁₂:Eu³⁺ red phosphors were synthesized at different temperatures using a solid state reaction method. The crystal structures, surface and optical properties of the Y₃Al₅O₁₂:Eu³⁺ red phosphors were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and photoluminescence (PL) analyses. From XRD results, the crystal structure of the Y₃Al₅O₁₂:Eu³⁺ red phosphors was determined to be cubic. The maximum emission spectra were observed for the Y₃Al₅O₁₂:Eu³⁺ red phosphor prepared by annealing for 4h at 1,700 ℃. The 565~590 nm photoluminescent spectra of the Y₃Al₅O₁₂:Eu³⁺ red phosphors is associated with the ⁵D₀ → ⁷F₂ magnetic dipole transition of the Eu³⁺ ions. The intensity of the photoluminescent spectra in the red phosphors is more dominant for the magnetic dipole transition than the electric dipole transition with increasing annealing temperature. The International Commission on Illumination (CIE) coordinates of Y₃Al₅O₁₂:Eu³⁺ red phosphors prepared by 1,700 ℃ annealing temperature are X = 0.5994, Y = 0.3647.

• Journal of the Korean institute of surface engineering
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• v.56 no.3
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• pp.208-218
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• 2023

Photocatalysts are advanced materials which accelerate the photoreaction by providing ordinary reactions with other pathways. The catalysts have various advantages, such as low-cost, low operating temperature and pressure, and long-term use. They are applied to environmental and energy field, including the air and water purification, water splitting for hydrogen production, sterilization and self-cleaning surfaces. However, commercial photocatalysts only absorb ultraviolet light between 100 and 400 nm of wavelength which comprises only 5% in sunlight due to the wide band gap. In addition, rapid recombination of electron-hole pairs reduces the photocatalytic performance. Recently, studies on blackening photocatalysts by laser, thermal, and plasma treatments have been conducted to enhance the absorption of visible light and photocatalytic activity. The disordered structures could yield mid-gap states and vacancies could cause charge carrier trapping. Herein, liquid phase plasma (LPP) is adopted to synthesize Ag-doped black ZnO for the utilization of visible-light. The physical and chemical characteristics of the synthesized photocatalysts are analyzed by SEM/EDS, XRD, XPS and the optical properties of them are investigated using UV/Vis DRS and PL analyses. Lastly, the photocatalytic activity was evaluated using methylene blue as a pollutant.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.7
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• pp.7-14
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• 2009

In this paper, the effects of annealing conditions on the structural ((002) intensity, FWHM, d-spacing, grain size, (002) peak position), optical (UV peak, UV peak position) and electrical properties (carrier concentrations, resistivity, mobility) of ZnO films were investigated. ZnO films were deposited onto SiO$_2$/si substrates by RF magnetron sputtering from a ZnO target. The substrate was not heated during deposition. ZnO films were annealed in temperature ranges of $500\sim650^{\circ}C$ in the O$_2$ flow for 5$\sim$20 min. The film average thicknesses were in the range of 291 nm. The surface morphologies and structures of the samples were characterize by SEM and XRD, respectively. The optical properties were evaluated by photoluminescence (PL) measurement at room temperature (RT) using a He-Cd 325 nm laser. As the annealing temperature and time vary, the following relations were also observed: (1) proportional relationships among UV intensity (002) intensity, and grain size exist, (2) UV intensity is inversely proportional to FWHM, (3) there is no special relationship between UV intensity and electron carrier concentrations, (4) d-spacing is inversely proportional to (002) peak position, (5) UV peak position in the range of 3.20$\sim$3.24 eV means that ZnO films have a n-type conductivity which was consistent with that obtained from the electrical property, (6) the optimal conditions for the best optical and structural characteristics were found to be oxygen fraction, (O$_2$/(O$_2$+Ar)) of 0.2, RF power of 240W, substrate temperature of RT, annealing condition of 600$^{\circ}C$ for 20 min, and sputtering pressure of 20 mTorr.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.71-76
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• 2017

The electrical behavior and flexibility of the screen printed Ag circuits were investigated with infrared radiation sintering times and sintering temperatures. Electrical resistivity and radio frequency characteristics were evaluated by using the 4 point probe measurement and the network analyzer by using cascade's probe system, respectively. Electrical resistivity and radio frequency characteristics means that the direct current resistance and signal transmission properties of the printed Ag circuit. Flexibility of the screen printed Ag circuit was evaluated by measuring of electrical behavior during IPC sliding test. Failure mode of the Ag printed circuits was observed by using field emission scanning electron microscope and optical microscope. Electrical resistivity of the Ag circuits screen printed on Pl substrate was rapidly decreased with increasing sintering temperature and durations. The lowest electrical resistivity of Ag printed circuit was up to $3.8{\mu}{\Omega}{\cdot}cm$ at $250^{\circ}C$ for 45 min. The crack length arisen within the printed Ag circuit after $10{\times}10^4$ sliding numbers was 10 times longer than that of after $2.5{\times}10^4$ sliding numbers. Measured insertion loss and calculated insertion loss were in good agreements each other. Insertion loss of the printed Ag circuit was increased with increasing the number of sliding cycle.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.9-13
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• 2018

In this work, we investigated the variation of optical characteristics with the thickness of bulk GaN grown by hydride vapor phase epitaxy(HVPE) to evaluate applicability as GaN substrates in fabrication of high-brightness optical devices and high-power devices. We fabricated 2-inch GaN substrates by using HVPE method of various thickness (0.4, 0.9, 1.5 mm) and characterized the optical property with the variation of defect density and the residual stress using chemical wet etching, Raman spectroscopy and photoluminescence. As a result, we confirmed the correlation of optical properties with GaN crystal thickness and applicability of high performance optical devices via fabrication of homoepitaxial substrate.

• KSBB Journal
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• v.14 no.6
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• pp.724-730
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• 1999

Characteristics and enzyme activity comparison was made between urokinase isolated from urine and pro-urokinase separated from CHO(Chinese Hamster Ovary) cell culture broth. Both of purified urokinase and pro-urokinase resulted 54Kd single band in electrophoresis. Urokinase which was proved as a single molecule by gel filtration showed two separated 33Kd and 21Kd bands by 2-mercaptoethanol reduction. Isoelectric forcusing resulted same pl value of 8.6 for both of them. N-terminal amino acid sequence of urokinase after 159th Ile was Ile-Gly-Gly-Glu-Phe-Thr-Thr-Ile-Glu which was different from another N-terminal sequence of Ser-Asn-Glu-Leu-His-Gln-Val-Pro-Ser-Asn. Thrombolytic activities of both of them were propotional to the enzyme concentration. Urokinase showed thrombolytic activities in an short period of reaction time. Pro-urokinase, however, showed high thrombolytic activity for 2 hours or longer period of reaction time.

• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.752-756
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• 2002

Green-emitting $Zn_2SiO_4:Mn$ phosphors for PDP(Plasma Display Panel) application were synthesized by colloidal seed-assisted spray pyrolysis process. The codoping with $Gd^{3+}/Li^+$, which replaces $Si^{4+}$ site in the willemite structure, was performed to improve the luminous properties of the $Zn_2SiO_4:Mn$ phosphors. The particles prepared by spray pyrolysis process using fumed silica colloidal solution had a spherical shape, small particle size, narrow size distribution, and non-aggregation characteristics. The $Gd^{3+}/Li^+$ codoping amount affected the luminous characteristics of $Zn_2SiO_4:Mn$ phosphors. The codoping with proper amounts of $Gd^{3+}/Li^+$ improved both the photoluminescence efficiency and decay time of $Zn_2SiO_4:Mn$ phosphor particles. In spray pyrolysis, the post-treatment temperature is another factor controlling the luminous performance of $Zn_2SiO_4:Mn$ phosphors. The $Zn_{1.9}SiO_4:Mn_{0.1}$ phosphor particles containing 0.1 mol% $Gd^{3+}/Li^+$ co-dopant had a 5% higher PL intensity than the commercial product and 5.7 ms decay time after post-treatment at $1,145^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.293-294
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• 2011

It is known that semiconductor quantum-dot (QD) heterostructures have superior zero-dimensional quantum confinement, and they have been successfully applied to semiconductor laser diodes (QDLDs) for optical communication and infrared photodetectors (QDIPs) for thermal images [1]. The self-assembled QDs are normally formed at Stranski-Krastanov (S-K) growth mode utilizing the accumulated strain due to lattice-mismatch existing at heterointerfaces between QDs and cap layers. In order to increase the areal density and the number of stacks of QDs, recently, sub-monolayer (SML)-thick QDs (SQDs) with reduced strain were tried by equivalent thicknesses thinner than a wetting layer (WL) existing in conventional QDs (CQDs) by S-K mode. Despite that it is very different from CQDs with a well-defined WL, the SQD structure has been successfully applied to QDIP[2]. In this study, optical characteristics are investigated by using photoluminescence (PL) spectra taken from self-assembled InAs/GaAs QDs whose coverage are changing from submonolayer to a few monolayers. The QD structures were grown by using molecular beam epitaxy (MBE) on semi-insulating GaAs (100) substrates, and formed at a substrate temperature of 480$^{\circ}C$ followed by covering GaAs cap layer at 590$^{\circ}C$. We prepared six 10-period-stacked QD samples with different InAs coverages and thicknesses of GaAs spacer layers. In the QD coverage below WL thickness (~1.7 ML), the majority of SQDs with no WL coexisted with a small amount of CQDs with a WL, and multi-peak spectra changed to a single peak profile. A transition from SQDs to CQDs was found before and after a WL formation, and the sublevel of SQDs peaking at (1.32${\pm}$0.1) eV was much closer to the GaAs bandedge than that of CQDs (~1.2 eV). These revealed that QDs with no WL could be formed by near-ML coverage in InAs/GaAs system, and single-mode SQDs could be achieved by 1.5 ML just below WL that a strain field was entirely uniform.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.443-450
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• 1993

Self-alignment gatc Schottky contact structure on Si- implanted GaAs was formed by plasma enhanced chemical vapor dcposirion. Tungsten nitride thin films (ahclut 1600$\AA$) \vcre dopositcd on GaAs at $350^{\circ}C$ in order to fahricarc GaAs 1Cs and ttwn rapidly annealed at $750^{\circ}C$ to $900^{\circ}C$. Thermal charac tcristics of PECVD)-$W_{67}N_{43}$/GaAs structure were investigated by X-ray diffraction, photolumintesccnce. and optical deep level transient specrroscopy. Results revealed that $W_{67}N_{33}$ gate was more thermally sta ble with GaAs substrate than W gate and Si atoms implanted In $W_{67}N_{33}$/GaAs structure became morr active than those In W/GaAs after annealing. I-V characteristics of $W_{67}N_{33}$/GaAs diod c exhibired a nearly ideal diode behavior. The termal stability of $W_{67}N_{33}$/GaAs diode was better than that of W/GaAs diode with the post annealing at temperatures from 800 to $900^{\circ}C$ for 20s without As overpressure.