• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.611-613
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• 2016

The characteristics of tunnel field-effect transistor(TFET) structure with source-overlapped gate was investigated using a TCAD simulations. Tunneling is mostly divided into line-tunneling and point-tunneling, and line-tunneling is higher performance than point-tunneling in terms of subthreshold swing(SS) and on-current. In this paper, from the simulation results of source-overlapped gate length effects at silicon(Si), germanium(Ge), Si-Ge hetero TFET structure, the guideline of optimal structure with highest performance are proposed.

• Journal of Navigation and Port Research
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• v.32 no.9
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• pp.723-727
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• 2008

Sensing performances of evanescent field absorption (EFA) hetero-core fiber sensor has been presented based on EFA by changing the length and the core diameter of the single mode fiber. Experimental results have demonstrated a good feature in their relationship between the length and the core diameter of the single mode fiber. The sensor consists of 2 fiber optics which have the same cladding diameter of $125{\mu}m$ However one fiber optic used is single mode and has varying core diameter ranging from 3.3 to $5.6{\mu}m$. The other fiber is multimode type and has a thicker fixed core diameter of $62.5{\mu}m$. The 2 fiber optics are thermally spliced together. Experiments conducted to measure the resonance wavelength were carried out over a range of refractive index, to find the optimum sensing length Experiments show that core diameter of the single mode fiber and sensing length offects the linearity and sensitivity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.250-254
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• 2006

Hetero-junction sheet actuator composed of carbon nanotubes and $V_{2}O_5$ nanowires were demonstrated in a bimetal configuration. The successive filtration of $V_{2}O_5$ nanowire solution followed by carbon nanotube dispersed water solution in the same way produced a dark-gray colored sheet. A significant actuation was observed in sodium chloride electrolyte solution with a bending direction to the carbon nanotube side at the positive bias voltage against the copper counter-electrode. As the frequency of the applied voltage increased, the amplitudes decreased, indicating a rather slow response of the hetero-film actuator in the electrolyte solution. The hybrid structure enabled an easy fabrication of the film actuator with the enhanced efficiencies.

• Korean Journal of Crystallography
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• v.1 no.2
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• pp.99-104
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• 1990

The hetero-epitaxial growth of AmB v type onto-electronic material is attempted by means of the laser-induced chemical vapour deposition technique. The bimolecular gas phase reaction of trimethylgallium with ammonia on (001) alumina substrate for the epitaxy of gallium nitride is chosen as a model system. In this study, ArF exciter laser (193nm) is employed as a photon source. Marked difference is found in nucleation and in subsequent crystal incorporation between the doposits formed with and without the laser-irradiation. The surface coverage with isomorphically grown drystallites is pronounced upon "volume-excited" irradiation in comparison with the conventional thermal process. As to the crystal structure of the grown layers, the laser-induced deposits of GaN may be represented by either of the following two models: (001) plane of sapphire //y (001) plane of wurtzite-type GaN, OR (001) plane of sapphire//(001) plane of wurtzite-type-GaN (111) plane of twinned zinc blende-type GaN.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.401-408
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• 2019

The objective of this study is to develop a new type of buried sensor module that can directly assess pre-stressed concrete by measuring strain using a hetero-core optical fiber sensor. In this regard, experiments were conducted to evaluate the performance of the sensor using an exposure sensor module. Based on the experimental results, when the values of the displacement control velocity were 0.12 mm/min and 1.80 mm/min, the corresponding delays in the measurement were 52.1 s and 2.6 s respectively, which indicated that the maximum delay between the two measurements was a factor of 19. Due to the measurement delay phenomena, the sensor module used in the experiments cannot be employed to check the real-time state of the structure. Thus, additional experiments were needed to develop a new sensor module that can measure the real-time state of the structure. To investigate the cause of the measurement delay phenomena, three experiments were conducted. It was confirmed that measurement delay is mainly attributed to frictional resistance. The measurement delay phenomena were not observed in the experiments using the friction-removed device.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.245-245
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• 2003

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.11a
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• pp.144-144
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• 2002

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.281-284
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• 1995

A molecular photodiode was fabricated with hetero-Langmuir-Blodgett (LB) film consisting of an electron accepter(A) and sensitizer. N-Allyl-N-[3-propylamido-N\",N\"-야(n-octadecyl)]-4,4-bipyridum Dibromide and 7,8-dimethyl-10-dodecyl isoalloxan-zine were used as A and S units, respectively. By aligning hefter-LB film of A/S units on ITO glass with an aluminium thin film, a molecular photodiode with the structure of Metal/Insulator/Metal(MIM) was constructed. Due to excitation by irradiation with a 460nm monochromatic light source, the photo-induced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The direction of energy flow was in accordance with the energy level profile across the LB films. The photo switching function was achieved and the rectifying characteristics was obserbed in the molecular devise.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.511-514
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• 1987

Langmuir-Blodgett (LB) films of TCNQ(tetracyanoquinodimethane) with alkyl radical($C_{12}TCNQ$) were prepared on the sample of Al/LB film/Al type where Al are electrode, and polarization in LB film and dipolar moment of molecules in the films were measured by TSC. $Al_2O_3$ layer was yielded on the electrode by natural oxidation in air. According to the cooperation of $Al_2O_3$ dielectric layer and the polarization of $C_{12}TCNQ$-LB film, the macroscopic electrical field was yielded in LB film and $Al_2O_3$ layer. The field strength in $C_{12}TCNQ$-LB films was evaluated at about $1{\times}10^6{\sim}5{\times}10^6\;V/cm$.