• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.201-206
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• 2005

In this work, we tried to improve the fabrication process in HVPE (Hydride Vapor Phase Epitaxy) system by using Si(111) substrate with pre-deposited Al layer. PL measurements was done for samples with and without pre-deposited Al on Si and it was also examined the dependence of the optical characteristic properties on AlN buffer thickness for GaN/AIN/Al/Si. A sample with thin Al nucleation layer on Si substrate reveals a better optical property than the other. And it suggests that the thickness for AlN buffer layer with thin Al nucleation layer on Si(111) substrate is most proper about $260{\AA}$ to grow GaN in HVPE system. The surface morphology of GaN clearly shows the hexagonal crystallization. The XRD pattern showed strong peak at GaN{0001} direction.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1022-1025
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• 2005

The effect of substrate surface to the formation of ZnO nanostructures has been investigated using Si (111), $Al_2O_3$(C-plane) $Al_2O_3$(A-plane), and $Al_2O_3$(R-plane) substrates. The growth temperature was controlled from 500$^{\circ}C$ ${\sim}$ 600$^{\circ}C$, and the luminescence properties were investigated by a series of photoluminescence (PL) measurements at the elevating temperatures. ZnO nanostructures grown on Si substrate show strong UV emission intensity along with green emission positioned at 3.22 eV and 2.5 eV, respectively. However, green emission was not observed from the ZnO nanostructures grown on $Al_2O_3$ substrates. It is explained in terms of the difference of the surface energy between Si and $Al_2O_3$. Also, the origin of UV emissions has been discussed by using the temperature-dependent PL. The distinction of the PL spectra is interpreted in terms of the difference of the impurity included in the nanostructures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.272-279
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• 2015

$Y_2O_3:Eu^{3+}$ is an excellent red-emitting phosphor, which has been widely used for display devices due to highly luminescent property and chemical stability. In this study, $Y_2O_3:Eu^{3+}$ red phosphors were prepared using the solid state reaction and RF thermal plasma synthesis. The particle size of $Y_2O_3:Eu^{3+}$ phosphors obtained by the solid state reaction varied from 10 to $20{\mu}m$, and 30~100 nanometer sized $Y_2O_3:Eu^{3+}$ particles were obtained from a liquid form of raw material through RF thermal plasma synthesis without an additional heat treatment. Photoluminescence measurements of the obtained $Y_2O_3:Eu^{3+}$ particles showed a red emission peak at 611 nm ($^5D_0{\rightarrow}^7F_2$). PL intensity of red nano phosphors prepared by RF thermal plasma synthesis was comparable to that of red phosphors prepared by the solid state reaction, indicating that nano-sized $Y_2O_3:Eu^{3+}$ red phosphors could be successfully synthesized using one-step process of RF thermal plasma.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.889-894
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• 2001

2wt% $Al_2O_3-doped$ ZnO (AZO) thin films were deposited on sapphire (0001) single crystal substrate by parellel type rf magnetron sputtering at 55$0^{\circ}C$. The as-grown AZO thin films was polycrystalline and showed only broad deep defect-level photoluminescence (PL). In order to examine the change of PL property, AZO thin films were annealed in $N_2$ (N-AZO) and $H_2$ (H-AZO) at the temperature of $600^{\circ}C$~$1000^{\circ}C$ through rapid thermal annealing. After annealed at $800^{\circ}C$, N-AZO shows near band edge emission (NBE) with very small deep-level emission, and then N-AZO annealed at $900^{\circ}C$ shows only sharp NBE with 219 meV FWHM. In Comparison with N-AZO, H-AZO exhibits very interesting PL features. After $600^{\circ}C$ annealing, deep defect-level emission was quire quenched and NBE around 382 nm (3.2 eV) was observed, which can be explained by the $H_2$passivation effect. At elevated temperature, two interesting peaks corresponding to violet (406 nm, 3.05 eV) and blue (436 nm, 2.84 eV) emission was firstly observed in AZO thin films. Moreover, peculiar PL peak around 694 nm (1.78 eV) is also firstly observed in all the H-AZO thin films and this is believed good evidence of hydrogenation of AZO. Based on defect-level scheme calculated by using the full potential linear muffin-tin orbital (FP-LMTO), the emission 3.2 eV, 3.05 eV, 3.84 eV and 1.78 eV of H-AZO are substantially deginated as exciton emission, transition from conduction band maximum to $V_{ Zn},$ from $Zn_i$, to valence band maximum $(V_{BM})$ and from $V_{o} to V_BM}$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.317-321
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• 2014

Hydrothermal synthesis technique could be carried out for growth of ZnO nanowires at relatively low process temperature, and it could be freely utilized with various substrates for fabrication process of functional electronic devices. However, it has also a demerit of relatively slow growth characteristics of the resulting ZnO nanowires. In this paper, an external DC bias of positive and negative 0.5 [V] was applied in the hydrothermal synthesis process for 2~8 [h] to prepare ZnO nanowires on a seed layer of AZO with high electrical conductivity. Growth characteristics of the synthesized ZnO nanowires were analyzed by FE-SEM. Material property of the grown ZnO nanowires was examined by PL analysis. The ZnO nanowires grown with positive bias revealed distinctively enhanced growth characteristics, and they showed a typical material property of ZnO.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2002.05a
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• pp.251-259
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• 2002

The design concept of diesel engines for sea-going ships has been directed to Low-speed/Long-Stroke type to improve the efficiencies of combustion and propelling. But the time-delay property inevitable at such low speed engines gives much difficulties for governors to control the engine speed because they would be apt to go into unstable region especially when operating at low speed. The purpose of this paper is to study the problem of how the governor gain can be calculated dynamically in accordance with the variance of engine speed at least for an engine to be stable. In this study, the property of diesel engine was described as composed of combustion element including dead time and rotating element, and the ultimate gain for the speed control system to be located on the condition of stability limit was proposed based on the frequency characteristics. And the target gains with optimized stability also were proposed by giving proper margin to these ultimate conditions. The results were applied to a model system and the availability was confirmed to be satisfactory.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.55-56
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• 2005

The properties of phosphorus doped ZnO thin films deposited on (001) sapphire substrates by pulsed laser deposition (PLD) were investigated depending on various deposition conditions. The phosphorus (P) doped ZnO target was composed of ZnO + x wt% Al (x=1, 3, 5). The structural, electrical and optical properties of the ZnO thin films were measured by X-ray diffraction (XRD), Hall measurements and photoluminescence (PL). As the deposition temperature optimized, the electrical properties of the phosphorus doped ZnO (ZnO:P) layer showed a electron concentration of $7.76\times10^{16}/cm^3$, a mobility of 10.225 $cm^2/Vs$, a resistivity of 7.932 $\Omega$cm. It was observed the electrical property of the film was changed by dopant activation effect as target variations and deposition conditions.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.25.2-25.2
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• 2009

Vertically aligned zinc oxide(ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate with different deposition condition. Based on the surface morphology, ZnO nanostructures are divided into three types: nanoneedles, nanonails and nanorods with rounded tip. Variable temperature photoluminescence (PL) have employed to probe the exciton recombination in high density and vertically aligned ZnO Nanorod arrays. Low temperature photoluminescence measurements do not show any significant yellow emission, but the near band edge excitonic emission shows very strong dependence with the surface morphology. The recombination properties are expected to be different due to different surface-to-volume ratio and distribution of potential fluctuations of intrinsic defects.

• Journal of the Korean Applied Science and Technology
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• v.15 no.3
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• pp.85-90
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• 1998

In this study, organic electroluminescent devices(OELD) with a structure of a glass $substrate/ITO/TPD/Tb(ACAC)_3(Phen-Cl)/Alq_3/Al$ was fabricated by vacuum evaporation method, where Tb complex was known to have green light emitting property. Electroluminescent(EL) and I-V characteristics of this structure were investigated. This triple-layer structure shows the green EL spectrum at the wavelwngth of 546nm, which is almost the same as the PL spectrum of $Pb(ACAC)_3(Phen_Cl)$. It was found in current-voltage(I-V) characteristics of the devices that the operating voltage was about 12V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.65-66
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• 2008

The realization and origin of p-type ZnO are main issue for photoelectronic devices based on ZnO material. N-doped and nominally undoped p-type ZnO films were achieved on silicon (100) and homo-buffer layers by RF magnetron sputtering and post in-situ annealing. The undoped film shows high hole mobility of 1201 $cm^2V^{-1}s^{-1}$ and low resistivity of $0.0454\Omega{\cdot}cm$ with hole concentration of $1.145\times10^{17}cm^{-3}$. The photoluminescence(PL) spectra show the emissions related to FE, DAP and defects of $V_{Zn}$, $V_O$, $Zn_O$, $O_i$ and $O_{Zn}$.