• Journal of Korean Society of Water and Wastewater
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• v.10 no.3
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• pp.73-82
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• 1996

The removal efficiencies of organic substrates, nitrogen and phosphorus in the anaerobic-aerobic biological phosphorus removal process were investigated by addition of acetic acid, propionic acid and butyric acid which are normal volatile fatty acids contained in anaerobic digester supernatants. Substrate utilization coefficients for the phosphorus release and uptake were also estimated. The effect of a VFA, which showed higher phosphorus removal efficiency than the other VFAs did, was also studied in an anaerobic-aerobic-anoxic biological nutrient removal process. For the anaerobic-aerobic process added by VFA, the phosphorus removal efficiencies were up to about 68%, 55% and 61% for the reactors of acetic acid, propionic acid and butyric acid added, respectively, which indicates the efficiencies were increased by about 8-21%, comparing to that of 47% for the reactor with no VFA added. There were no significant difference in removal efficiencies for organic substrate and $NH_3-N$ without regard to addition of VFA. However, the removal efficiency of total nitrogen was increased in the case of VFA added, since $NO_3-N$ was less produced. For the anaerobic-aerobic-anoxic process added VFA, the removal efficiencies for $NH_3-N$ and $PO{_4}^{3-}-P$ were increased by 5% and 13%, respectively, comparing with them in the reactors not added VFA.

• Solar Energy
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• v.5 no.2
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• pp.46-53
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• 1985

Hydrogenated amorphous silicon solar cells which are fabricated by photo-chemical vapor deposition (photo-CVD) system has been investigated. In the photo-CVD system which consists of three separate reaction chambers, low-pressure mercury lamp has been used as a light source. The main reactant ($Si_2H_6/He$) gases which are premixed with a small amount of mercury vapor in a mercury-vaporizer kept at $50^{\circ}C$ have been used. Using $C_2H_2$ and $SiH_2(CH_3)_2$ as the carbon source, p-type wide band gap a-SiC:H films have been obtained. The result has been found that the undoped layers of the pin/substrate solar cells are influenced by the residual impurities, such as phosphorus and boron during the deposition process. By minimizing the effect of the impurities in the i-layer and optimizing conditions at the p-layer and p/i interface, the energy conversion efficiency of 9.61 % under AM-1 ($100mW/Cm^2$) has been achieved for pin/substrate solar cells illuminated through their p-layers, using the three separate reaction chamber apparatus. It is expected that a-SiC:H solar cells with the energy conversion efficiency over 10% have been fabricated by Photo-CVD method.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.7-10
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• 2022

A functional polyethylene terephthalate substrate to increase light extraction efficiency of organic light-emitting diodes is studied. We formed nano-structured PET surfaces by controlling the power, gas, and exposure time of the linear ion-beam. The haze of the polyethylene terephthalate can be controlled from 0.2% to 76.0% by changing the peak-to-valley roughness of nano structure by adjusting the exposure cycle. The treated polyethylene terephthalate shows average haze of 76.0%, average total transmittance of 86.6%. The functional PET increases the current efficiency of organic light-emitting diodes by 47% compared to that of organic light-emitting diode on bare polyethylene terephthalate. In addition to polyethylene terephthalate with light extraction performance, by conducting additional research on the development of functional PET with anti-reflection and barrier performance, it will be possible to develop flexible substrates suitable for organic light-emitting diodes lighting and transparent flexible displays.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.273-276
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• 2011

Ultraviolet (UV) light emitting diodes (LEDs) were grown on a patterned n-type GaN substrate (PNS) with 200 nm silicon-di-oxide (SiO2) nano pattern diameter to improve the light output efficiency of the diodes. Wet etched self assembled indium tin oxide (ITO) nano clusters serve as a dry etching mask for converting the SiO2 layer grown on the n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. PNS is obtained by n-GaN regrowth on the SiO2 nano patterns and UV-LEDs were fabricated using PNS as a template. Two UV-LEDs, a reference LED without PNS and a 200 nm PNS UV-LEDs were fabricated. Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) and Light output intensity- Input current- Voltage (L-I-V) characteristics were used to evaluate the ITO-$SiO_2$ nanopattern surface morphology, threading dislocation propagation, PNS crystalline property, PNS optical property and UVLED device performance respectively. The light out put intensity was enhanced by 1.6times@100mA for the LED grown on PNS compared to the reference LED with out PNS.

• Korean Journal of Materials Research
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• v.24 no.12
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• pp.645-651
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• 2014

GaN is most commonly used to make LED elements. But, due to differences of the thermal expansion coefficient and lattice mismatch with sapphire, dislocations have occurred at about $109{\sim}1010/cm^2$. Generally, a low temperature GaN buffer layer is used between the GaN layer and the sapphire substrate in order to reduce the dislocation density and improve the characteristics of the thin film, and thus to increase the efficiency of the LED. Further, patterned sapphire substrate (PSS) are applied to improve the light extraction efficiency. In this experiment, using an AlN buffer layer on PSS in place of the GaN buffer layer that is used mainly to improve the properties of the GaN film, light extraction efficiency and overall properties of the thin film are improved at the same time. The AlN buffer layer was deposited by using a sputter and the AlN buffer layer thickness was determined to be 25 nm through XRD analysis after growing the GaN film at $1070^{\circ}C$ on the AlN buffer CPSS (C-plane Patterned Sapphire Substrate, AlN buffer 25 nm, 100 nm, 200 nm, 300 nm). The GaN film layer formed by applying a 2 step epitaxial lateral overgrowth (ELOG) process, and by changing temperatures ($1020{\sim}1070^{\circ}C$) and pressures (85~300 Torr). To confirm the surface morphology, we used SEM, AFM, and optical microscopy. To analyze the properties (dislocation density and crystallinity) of a thin film, we used HR-XRD and Cathodoluminescence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.314-315
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• 2008

We have studied a property change of organic light-emitting diodes (OLED)s due to a surface reformation of indium-tin-oxide(ITO) substrate. An ITO is widely used as a transparent electrode in light-emitting diodes, and the OLEDs device performance is sensitive to the surface properties of the ITO. The ITO surface reformation could reduce the Schottky barrier at the ITO/organic interface and increase the adhesion of the organic layer onto the electrode. We have studied the characteristics of OLEDs with a treatment by a wet processing of the ITO substrate. The self-assembled monolayer(SAM) was used for wet processing. The characteristics of OLEDs were improved by SAM treatment of an ITO in this work. The OLEDs with a structure of ITO/TPD(50nm)/$Alq_3$(70nm)/LiF(0.5nm)/Al(100nm) were fabricated, and the surface properties of ITO were investigated by using seneral characterization techniques. Self-assembled monolayer introduced at the anode/organic interface gave an improvement in turn-on voltage, luminance and external quantum efficiency compared to the device without the SAM layer. SAM-treatment time of the ITO substrate was made to be 0/10/15/20/25min. The current efficiency of the device with 15min. treated SAM layer was increased by 3 times and the external quantum efficiency by 2.6 times.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.1
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• pp.1-5
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• 2010

In this paper, we directly compare the program efficiency of conventional channel hot electron (CHE) injection methods and a novel hot electron injection methods using substrate forward biases in our silicon-oxide-nitride-oxide-silicon (SONOS) cell. Compared with conventional CHE injection methods, the proposed injection method showed improved program efficiency including faster program operation at lower bias voltages as well as localized trapping features for multi-bit operation with a threshold voltage difference of 1 V at between the forward and reverse read. This program method is expected to be useful and widely applied for future nano-scale multi-bit SONOS memories.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.636-641
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• 2012

In this study, we have investigated highly efficient nanoscale surface corrugated light emitting diodes (LEDs) for the enhancement of light extraction efficiency (LEE) of nitride semiconductor LEDs. Nanoscale indium tin oxide (ITO) surface corrugations are fabricated by using the conformal nanoimprint technique; it was possible to observe an enhancement of LEE for the ITO surface corrugated LEDs. By incorporating this novel method, we determined that the total output power of the surface corrugated LEDs were enhanced by 45.6% for patterned sapphire substrate LEDs and by 41.9% for flat c-plane substrate LEDs. The enhancement of LEE through nanoscale surface corrugations was studied using 3-dimensional Finite Different Time Domain (FDTD) calculation. From the FDTD calculations, we were able to separate the light extraction from the top and bottom sides of device. This process revealed that light extraction from the top and bottom sides of a device strongly depends on the substrate and the surface corrugation. We found that enhanced LEE could be understood through the mechanism of enhanced light transmission due to refractive index matching and the increase of light scattering from the corrugated surface. LEE calculations for the encapsulated LEDs devices also revealed that low LEE enhancement is expected after encapsulation due to the reduction of the refractive index contrast.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.294-300
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• 2009

To improve the output power of a photomixer as a THz source, we propose a four-leaf clover-shaped antenna structure which is composed of a highly resonant radiation element and a stable DC feed element. The resonance characteristics of the proposed structure were investigated on a half-infinite substrate first as a simplified radiation environment in order to save the computation time. Based on the antenna characteristics on a half-infinite substrate, the antenna structure was designed to have a maximum total efficiency and a maximum directivity on an extended hemispherical lens. In comparison with a full-wavelength dipole, an input resistance of this structure increased six fold and this characteristic significantly improved the mismatch efficiency between a photomixer and an antenna. THz output power from this structure is expected to increase by 2.7 times as compared to a full-wavelength dipole case.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.902-905
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• 2012

This study is explore the photoelectric conversion change of dye-sensitized solar cells with surface treatment of the conductive substrate. gases of FTO surface treatment were $N_2$, and $O_2$. Treatment conditions of surface were gas flux from 25 sccm to 50 sccm and RF power were from 25 W to 50 W. Treatment time and pressure were fixed 5 min and 100 mtoor. The best sheet resistance and surface roughness were obtained by $O_2$ 50 sccm and 50 W and that result were 7.643 ${\Omega}/cm^2$ and 17.113 nm, respectively. The best efficiency result was obtained by $O_2$ 50 sccm and 50 W and that result of Voc, Jsc, FF and efficiency were 7.03 V, 14.88 $mA/cm^2$, 63.75% and 6.67%, respectively.