• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.6
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• pp.447-452
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• 1998

The selective dry etching of GaAs to Al\ulcornerGa\ulcornerAs using $BCI_3/SF_6$ gas mixture in electron cyclotron resonance(ECR) plasma is investigated. A selectivity of GaAs to AlGaAs of more than 100 and maximum etch rate of GaAs are obtained at a gas ratio $SF_6/BCI_3+SF_6$ of 25%. We verified the formation of $AlF_3$ on $Al_{0.25}Ga_{0.75}As$from the Auger spectra which enhanced the etch selectivity. In order to investigate surface damage of AlGaAs caused by ECR plasma, we performed a low temperature photoluminescence(PL) measurement as a function of RF power. As the RF power. As the RF power increases, the PL intensity decreases monotonically from 50 to 100 Wand then repidly decreases until 250 W. This behavior is due to surface damage by plasma treatment. This dry etching technique using $BCI_3/SF_6$ gas mixture in ECR plasma is suitable for gate recess formation on the GaAs based pseudomorphic high electron mobility transistor(PHEMT)

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.322-323
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• 2006

The nano-sized Ce-doped YAG(Yttrium Aluminum Garnet, $Y_3Al_5O_{12}$) phosphor powders were prepared by combustion method from a mixed aqueous solution of metal nitrates, using citric acid as a fuel. The luminescence formation process and structure of phosphor powders were investigated by means of XRD, SEM and PL. The XRD patterns show that YAG phase can form at all of the $Ce^{3+}$ concentration. However, when $Ce^{3+}$ concentration is over 2.0mol%, XRD patterns show $CeO_2$ peak between (321) peak and (400) peak. The pure crystalline YAG:Ce with uniform size of 30nm was obtained at 0.6mol% of the $Ce^{3+}$ concentration. The crystalline YAG:Ce powders showed broad emission peaks in the range 475~630nm and had maximum intensity at 526nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1010-1014
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• 2004

High quality GaN layer and $In_xGa_{1-x}N$ alloy were obtained on (0001)sapphire substrate using ammonia$(NH_3)$ and dimethylhydrazine$(DMH_y)$ as a nitrogen source by gas source molecular hem epitaxy(GSMBE) respectively. As a result, RHEED is used to investigate the relaxation processes which take place during the growth of GaN and $In_xGa_{1-x}N$. The full Width at half maximum of the x-ray diffraction(FWHM) rocking curve measured from Plane of GaN has exhibitted as narrow as 8 arcmin. Photoluminescence measurement of GaN and $In_xGa_{1-x}N$ were investigated at room temperature, where the intensity of the band edge emission is much stronger than that of deep level emission. In content of $In_xGa_{1-x}N$ epitaxial layer according to growth condition was investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.106-108
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• 2004

We have investigated the photolithographic patterning method of light emitting polymer film for polymer light emitting diodes (PLED). Blue light emitting polymers based on polyfluorene, which can be cured photochemically to yield an insoluble form, have been synthesized using Ni(0) mediated Yamamoto polymerization. The relationship between patterning property and several variables such as the intensity of the exposed UV light, the concentrations of additives, has been studied by using optical microscope analysis, UV/visible spectroscopy, and photoluminescence. We have successfully fabricated PLEDs composed of the patterned emissive layer and their electroluminescence property has been also investigated. In this presentation, the detailed photolithographic patterning method and its application for polymer light emitting display will be discussed.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.743-746
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• 2003

We have successfully used hydrophobic direct-wafer bonding, along with H-induced layer splitting of Ge, to transfer 700nm think, single-crystal Ge films to Si substrates. Optical and electrical properties have been also observed on these samples. Triple-junction solar cell structures gown on these Ge/Si heterostructure templates show comparable photoluminescence intensity and minority carrier lifetime to a control structure grown on bulk Ge. When heavily doped p$^{+}$Ge/p$^{+}$Si wafer bonded heterostructures were bonded, ohmic interfacial properties with less than 0.3Ω$\textrm{cm}^2$ specific resistance were observed indicating low loss thermal emission and tunneling processes over and through the potential barrier. Current-voltage (I-V) characteristics in p$^{+}$Ge/pSi structures show rectifying properties for room temperature bonded structures. After annealing at 40$0^{\circ}C$, the potential barrier was reduced and the barrier height no longer blocks current flow under bias. From these observations, interfacial atomic bonding structures of hydrophobically wafer bonded Ge/Si heterostructures are suggested.ested.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.333-337
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• 2005

In order to improve the performance of green emitting phosphors for plasma display panel, the $Zn_2SiO_4:Mn,Al$ phosphors were synthesized using sol-gel technique and studied using SEM and VUV photoluminescence spectrometer. pH values of the starting solutions (pH = 0.5$\~$2.34) were controled by HCl as the catalysis of hydrolysis and wet gels were dried at $80^{\circ}C$ and $120^{\circ}C$, respectively. We investigated the effects of pH and drying temperatures during sol-gel processes. The results indicated that the phosphor prepared at pH = 1 showed the maximum emission intensity in both drying conditions and the effect of pH of the starting solution on morphology were increased with particle size as HCl and phosphor dried at high temperature showed more spherical and smaller particles than at low.

• Rapid Communication in Photoscience
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• v.4 no.3
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• pp.70-72
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• 2015

Oligomers of p-phenylene vinylene and its derivatives have drawn much attention due to their unusual emission characteristics of showing increased emission when they form into nanoparticles. We have investigated the optical properties of the oligo-(p-phenylene vinylene) and its cyano-substituted derivatives in solution and in nanoaggregate media by femtosecond and picosecond time resolved fluorescence as well as stationary spectroscopies. All the spectroscopic data are consistent with the conclusion that the cyano substitution on the ${\beta}$-position of oligo-(p-phenylene vinylene) leads to breakage of the otherwise planar structure of cyano-unsubstituted molecules, which opens up an extremely efficient, as fast as 100 fs, non-radiative relaxation channel of the excited state. Formation of the nanoaggregates reverts the effect to make the molecules planar and to block the non-radiative relaxation channel. Therefore, concerning the applications in organic electroluminescent devices and organic light emitting diodes, substitution by the cyano group is not advantageous, although such modification should be useful in respect of controlling fluorescence intensity in different media.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.127-128
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• 2012

ZnO nanostructures were grown by the hydrothermal method on ZnO seed layers post-heated in the range $350-500^{\circ}C$. The effects of the post-heated ZnO seed layers on the structural and optical properties of the ZnO nanostructures were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and photoluminescence (PL) spectroscopy. The average grain sizes in the ZnO seed layers increased with increasing post-heating temperature, and nano-fibrous structures were observed on the surface of the ZnO seed layers post-heated at $450^{\circ}C$. The ZnO seed layers post-heated in the range $350-500^{\circ}C$ affected the residual stress, lattice distortion in the ZnO nanostructures and the intensity, positions, and full widths at half maximum of the 2-theta and PL peaks in the XRD and PL spectra for the ZnO nanostructures.

• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.206-211
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• 2015

We investigated the formation of a nanopyramidal structure and fabricated nanotextured Si solar cells using an Ag metal-assisted chemical etching process. The nanopyramidal structure was formed on a Si flat surface and the nanotexturing process was performed on the p-type microtextured Si surface. The nanostructural formation shows a transition from nanopits and nanopores to nanowires with etching time. The nanotextured surfaces also showed the photoluminescence spectra with an enhanced intensity in the wavelength range of 1,100~1,250 nm. The photoreflectance of the nanotextured Si solar cells was strongly reduced in the wavelength range of 337~596 nm. However, the quantum efficiency is decreased in the nanotextured samples due to the increased nanosurface recombination. The nanotexturing process provides a better p-n junction impedance of the nanotextured cells, resulting in an enhanced shunt resistance and fill factor which in turn renders the possibility of the increased conversion efficiency.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2213-2216
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• 2009

A novel carbazole functionalized bis-$\beta$-diketone type organic ligand, 1,1′-(2,6-bispyridyl)bis-3-(9-ethylcarbazole- 3-yl)-1,3-propanedione ($H_2L$) and its corresponding lanthanide complexes $Eu_2(L)_3\;and\;Tb_2(L)_3$ were successfully prepared. The ligand and complexes were characterized in detail based on FT-IR spectra, $^1H$ NMR and elemental analysis. The observed UV-Vis absorption and photoluminescence properties of the complexes were investigated, it shows that the Eu(III) and Tb(III) ions can be sensitized efficiently by the ligand ($H_2L$) to some extent, in particular, the complex $Tb_2(L)_3$ exhibits a more excellent luminescence property than the Eu(III) complex. Meanwhile, the introduction of the carbazole moiety can enlarge the $\Pi$-conjugated system of the ligand and enhance the luminescent intensity of the complexes. The results show that the complexes would be used as excellent luminescent materials.