• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.283-289
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• 2003

In this paper, we proposed novel multilayer photonic bandgap(PBG) structure using DSL(Descended Signal Line). From measurement result, the proposed PBG structure using DSL is reduced 72 % at size and increased 13 % at bandwidth compared to typical multilayer DGS(Defected Ground Structure). It is also reduced 42 % at size and increased 23 % at bandwidth compared to PBG structure using EGP(Elevated Ground Plane). In case of measurement for manufactured six PBG patterns, all patterns have the same cutoff frequency and bandstop characteristics. So it can be used for bandstop filter having very precise tolerance of below 300 MHz at 20 ㎓ if it is applied to real product and this filter will be useful for small microwave integrated circuit and module development.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.671-675
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• 2010

Gallium nitride (GaN), wide bandgap semiconductor, has attracted much attention because they are projected to have much better performance than silicon. In this paper, effects of design parameters change of GaN power static induction transistor (SIT) on the electrical characteristics (breakdown voltage, on resistance) were analyzed by computer simulation. According to the analyzed results, the optimization was performed to get power GaN SIT that has 600 V class breakdown voltage. As a result, we could get optimized 600 V class power GaN SIT that has higher breakdown voltage and lower On resistance with a thin (a several micro-meters) thickness of the channel layer.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.62.1-62.1
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• 2011

The structural, optical, and electrical properties of Ga-doped ZnO (GZO) thin films on glass substrates grown by radio-frequency(RF) magnetron sputtering were investigated. The flow ratio of Ar was varied as a deposition parameter for growing high-quality GZO thin films. The structural properties and surface morphologies of GZO were characterized by the X-ray diffraction. To analyze the optical properties of GZO, the optical absorbance was measured in the wavelength range of 300-1100 nm by using UV-VIS spectrophotometer. The optical transmittance, absorption coefficient, and optical bandgap energy of GZO thin films were calculated from the measured data. The crystallinity of GZO thin films is improved and the bandgap energy increases from 3.08 to 3.23eV with the increasing Ar flow ratio from 10 to 100 sccm. The average transmittance of the films is over 88% in the visible range. The lowest resistivity of the GZO is $6.215{\times}10^{-4}{\Omega}{\cdot}cm$ and the hall mobility increases with the increasing Ar flow ratio. We can optimize the characteristics of GZO as a transparent electrode for thin film solar cells by controlling Ar flow ratio during deposition process.

• Korean Journal of Optics and Photonics
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• v.21 no.5
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• pp.200-205
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• 2010

We report temperature and strain sensing characteristics of two kinds of in-line fiber interferometers. One interferometer consists of a section of Hollow Optical Fiber(HOF) spliced between two Photonic Bandgap Fibers(PBGF) and the other is built by splicing a section of HOF between two Large Mode Area-Photonic Crystal Fibers(LMA-PCF). To minimize the splice losses, we carefully optimized the heating time and arc current of the splicer so as not to collapse the air holes of the fiber. It is found that the first interferometer has a temperature sensitivity of 15.4 pm/$^{\circ}C$ and a strain sensitivity of 0.24 pm/${\mu}\varepsilon$. The other interferometer exhibits a temperature sensitivity of 17.4 pm/$^{\circ}C$ and a strain sensitivity of 0.2 pm/${\mu}\varepsilon$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.93-93
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• 2003

Photoluminescence(PL) properties of Silicon nanocrystals (nc-Si) as a function of temperature is reported to consider the mechanism of PL. Nc-Si has been made by $Si^+$ ion-implantation into thermal $SiO_2$ and subsequent annealing. And after gold had been diffused at the same samples above, the resultant PL spectra has been compared to the PL spectra from the non-gold doped nc-Si. PL peak energy variation from nc-Si is same with the variation of energy bandgap of bulk silicon as temperature changes from 6 K to room temperature. This result may mean nc-Si is still indirect transition material like bulk silicon. Gold doped nc-Si reveals short peak wavelength of PL spectrum than gold undoped one. PL peak shift through gold doing process shows clearly the PL mechanism is not from defect or interface states. PL intensity increases from 6K to a certain temperature and then decrease to room temperature. This characteristic with temperature shows that phonon have a role for the luminescence as theory explains that electron and hole can be recombined radiatively by phonon's assist in nc-Si, which is almost impossible in bulk silicon. Therefore luminescence is observed in nc-Si constructed less than a few of unit cell and the peak energy of luminescence can be higher than the bulk bandgap energy by the bandgap widening effect occurs in nanostructure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1182-1190
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• 2001

In this paper, microstrip photonic bandgap (PBG) structure with special perforation patterns etched on the line itself is analyzed and optimized in shape, then used for harmonic tuning of power amplifier. This PBG has an advantage in being fabricated and grounded. The dimension of unit lattice is enlarged vertically, but its input and output line maintain 50 Ω using tapered line. This modification from original structure can lessen possible error in etching PCB. The analysis and design of PBG structure are acquired from using EM simulation. The measured insertion loss of the final structure is 0.3 ∼0.4 dB, and its bandwidth of stopband is 6∼7 GHz. Measured results of improved characteristics by using PBG structure at the output of the power amplifier are 0.72∼0.99 dB in output power, 1.14∼7.8 % in PAE, and 1 dBc in the third IMD.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.9
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• pp.38-48
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• 2000

This paper presents the photonic bandgap structure that has a defect mode within a broad stopband. In order to create a broad stopband, we eliminated one of periodic stopbands of PBG structure by using a quarter-wavelength transformer and cascaded another PBG structure having a center frequency corresponding to the eliminated stopband. We have demonstrated that it is a simple and effective method that can solve an overlapping problem of periodic stopband in two cascaded PBG structures.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.695-698
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• 2017

ZnMgBeGaO/Ag/ZnMgBeGaO multilayer structures were sputter grown and characterized in detail. Results indicated that the electrical properties of the ZnMgBeGaO films were significantly improved by inserting an Ag layer with proper thickness (~ 10 nm). Structures with thicker Ag films showed much lower optical transmission, although the electrical conductivity was further improved. It was also observed that the electrical properties of the multilayer structure were sizably improved by annealing in vacuum (~35 % at $300^{\circ}C$). The optimum ZnMgBeGaO(20nm)/Ag(10nm)/ZnMgBeGaO(20nm) structure exhibited an electrical resistivity of ${\sim}2.6{\times}10^{-5}{\Omega}cm$ (after annealing), energy bandgap of ~3.75 eV, and optical transmittance of 65 % ~ 95 % over the visible wavelength range, representing a significant improvement in characteristics versus previously reported transparent conductive materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.308-310
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• 2022

Ultrawide bandgap gallium oxide (Ga₂O₃) semiconductors are known to have excellent photocatalytic properties due to their high redox potential. In this study, CO₂ reduction is demonstrated using nanostructured Ga₂O₃ photocatalyst under ultraviolet (254 nm) light source conditions. After the CO₂ reduction, C₂H₄ remained as a by-product in this work. Nanostructured Ga₂O₃ photocatalyst also showed an excellent endurance characteristic. Photogenerated electron-hole pairs boosted the CO₂ reduction to C₂H₄ via nanostructured Ga₂O₃ photocatalyst, which is attributed to the ultrawide and almost direct bandgap characteristics of the gallium oxide semiconductor. The findings in this work could expedite the realization of CO₂ reduction and a simultaneous C₂H₄ production using a low cost and high performance photocatalyst.

• Nanomaterials
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• v.11 no.3
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• pp.767-780
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• 2021

Tin sulfide polymorph (π-SnS) nanoparticles exhibit promising optoelectrical characteristics for photovoltaic and hydrogen production performance, mainly because of the possibility of tuning their properties by adjusting the synthesis conditions. This study demonstrates a chemical approach to synthesize π-SnS nanoparticles and the engineering of their properties by altering the Sn precursor concentration (from 0.04 M to 0.20 M). X-ray diffraction and Raman studies confirmed the presence of pure cubic SnS phase nanoparticles with good crystallinity. SEM images indicated the group of cloudy shaped grains, and XPS results confirmed the presence of Sn and S in the synthesized nanoparticles. Optical studies revealed that the estimated energy bandgap values of the as-synthesized π-SnS nanoparticles varied from 1.52 to 1.68 eV. This work highlights the effects of the Sn precursor concentration on the properties of the π-SnS nanoparticles and describes the bandgap engineering process. Optimized π-SnS nanoparticles were used to deposit nanocrystalline π-SnS thin films using the drop-casting technique, and their physical properties were improved by annealing (300 ℃ for 2 h).