• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.42.2-42.2
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• 2010

Transparent conducting oxides (TCOs) are of significant importance for their applications in various devices, such as light-emitting diodes, thin-film solar cells, organic light-emitting diodes, liquid crystal displays, and so on. In order for TCOs to contribute to the performance improvement of these devices, TCOs should have high transmittance and good electrical properties simultaneously. Sn-doped $In_2O_3$ (ITO) is the most commonly used TCO. However, indium is toxic and scarce in nature. Thus, ZnO has attracted a lot of attention because of the possibility for replacing ITO. In particular, group III impurity-doped ZnO showed the optoelectronic properties comparable to those of ITO electrodes. Al-doped ZnO exhibited the best performance among various doped ZnO films because of the high substitutional doping efficiency. However, in order for the Al-doped ZnO to replace ITO in electronic devices, their electrical and optical properties should further significantly be improved. In this connection, different ways such as a variation of deposition conditions, different deposition techniques, and post-deposition annealing processes have been investigated so far. Among the deposition methods, RF magnetron sputtering has been extensively used because of the easiness in controlling deposition parameters and its fast deposition rate. In addition, when combined with post-deposition annealing in a reducing ambient, the optoelectronic properties of Al-doped ZnO films were found to be further improved. In this presentation, we deposited Al-doped ZnO (ZnO:$Al_2O_3$ = 98:2 wt%) thin films on the glass and sapphire substrates using RF magnetron sputtering as a function of substrate temperature. In addition, the ZnO samples were annealed in different conditions, e.g., rapid thermal annealing (RTA) at $900^{\circ}C$ in $N_2$ ambient for 1 min, tube-furnace annealing at $500^{\circ}C$ in $N_2:H_2$=9:1 gas flow for 1 hour, or RTA combined with tube-furnace annealing. It is found that the mobilities and carrier concentrations of the samples are dependent on growth temperature followed by one of three subsequent post-deposition annealing conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.172-173
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• 2012

Currently GaN based LED is known to show high internal or external efficiency at low current range. However, this LED operation occurs at high current range and in this range, a significant performance degradation known as 'efficiency droop' occurs. Auger process, carrier leakage process, field effect due to lattice mismatch and thermal effects have been discussed as the causes of loss of efficiency, and these phenomena are major hindrance in LED performance. In order to investigate the main effects of efficiency loss and overcome such effects, it is essential to obtain relative proportion of measurements of internal quantum efficiency (IQE) and various radiative and nonradiative recombination processes. Also, it is very important to obtain radiative and non-radiative recombination times in LEDs. In this research, we measured the IQE of InGaN/GaN multiple quantum wells (MQWs) LEDs with PSS and Planar substrate using modified ABC equation, and investigated the physical mechanism behind by analyzing the emission energy, full-width half maximum (FWHM) of the emission spectra, and carrier recombination dynamic by time-resolved electroluminescence (TREL) measurement using pulse current generator. The LED layer structures were grown on a c-plane sapphire substrate and the active region consists of five 30 ${\AA}$ thick In0.15Ga0.85N QWs. The dimension of the fabricated LED chip was $800um{\times}300um$. Fig. 1. is shown external quantum efficiency (EQE) of both samples. Peak efficiency of LED with PSS is 92% and peak efficiency of LED with planar substrate is 82%. We also confirm that droop of PSS sample is slightly larger than planar substrate sample. Fig. 2 is shown that analysis of relation between IQE and decay time with increasing current using TREL method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.411-416
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• 2020

An optical arrangement has been set inside a photo-spectrometer to measure the reflectance of IR optics materials in mid IR range. The optical arrangement consists of equally spaced 4 gold coated full reflecting mirrors with the incidence angle of 45°. Baseline beam intensity I_B has been measured while the beam proceeds through the 4 mirrors. Reflectance of a mirror has been estimated from the I_B. And the beam intensity I_S with the specimen in the optical path has been measured with the 4th mirror replaced with the specimen. Reflectance of the specimen has been estimated from the value of I_S/I_B. Then the estimated reflectance has been put in Fresnel equation relating reflectance and refractive index(RI) to estimate the RI of the material. Measurement has been made for sapphire, germanium, magnesium fluoride, and zinc sulfide. The estimated RI of the materials are closely matching with reference data and the maximum difference less than 2% over the wavelength range 3-5㎛ for all materials tested. As an FT-IR photo-spectrometer with a broadband wavelength infrared light source is used, this method has the advantage of measuring the refractive index at multiple wavelengths in a single measurement.

• The korean journal of orthodontics
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• v.32 no.6 s.95
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• pp.443-453
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• 2002

The principal aims of this study were to identify the composition of salivary pellicles formed on various orthodontic brackets and to obtain a detailed information about the protein adsorption profiles from whole saliva and two major glandular salivas. Four different types of orthodontic brackets were used. All were upper bicuspid brackets with a $022{\times}028$ slot Roth prescription; stainless steel metal, monocrystalline sapphire, polycrystalline alumina, and plastic brackets. Bracket pelicles were formed by the incubation of orthodontic brackets with whole saliva, submandibular-sublingual saliva, and parotid saliva for 2 hours. The bracket pellicles were extracted and confirmed by employing sodium dodecyl sulfatepolyacrylamide gel electrophoresis, Western transfer methods, and immunodetection. The results showed that low-molecular weight salivary mucin, ${\alpha}-amylase$, secretory IgA (sIgA), acidic proline-rich proteins, and cystatins were attached to all of these brackets regardless of the bracket types. High-molecular weight mucin, which promotes the adhesion of Streptococcus mutans, did not adhere to uy orthodontic brackets. Though the same components were detected in all bracket pellicles, however, the gel profiles showed qualitatively and quantitatively different pellicles, according to the origins of saliva and the bracket types. In particular, the binding of sIgA was more prominent in the pellicles from parotid saliva and the binding of cystatins was prominent in the pellicles from the form plastic brackets. This study indicates that numerous salivary proteins adhere to the orthodontic brackets and these salivary proteins adhere selectively according to bracket types and the types of the saliva.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.113-116
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• 2010

We report on the growth and characteristics of the structural and optical properties of InGaN nano-structures doped with antimony (Sb) as a catalyst. The use of catalyst has been explored to modify the growth and defect generation during strained layer heteroepitaxial growth. We performed the growth of the InGaN nano-structures on c-sapphire substrates using mixed-source hydride vapor phase epitaxy (HVPE). The characteristic of samples was measured by scanning electron microscope (SEM) and photoluminescence (PL). The aligning direction of c-axis of the InGaN nano-structures was changed from vertical to parallel or inclined to the surface of substrates when the Sb was added as a catalyst. The indium composition was estimated about 3.2% in both cases of with or without the addition of Sb in the InxGal-xN structures. From the results of InGaN nano-structures formed with the addition of Sb, we can expect the performance of optical devices would be more improved by reduced piezo-electric field if we use the InGaN nano-structures of which c-axes are aligned parallel to the substrates as an active layer.

• Journal of the Mineralogical Society of Korea
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• v.18 no.4 s.46
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• pp.313-323
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• 2005

XRD, XRF, EPMA, FT-IR, and SEM-CL studies were carried out in order to characterize gemological features of corundum from Tanzania. Fluorescence reaction of the Tanzanian corundum to short and long wave ultraviolet rays was weakly detected. Inclusions in Tanzanian corundum are divided into five types, Type I is fluid-rich inclusion, Type II is gas-rich inclusion, Type III is liquid $CO_{2}$ inclusion, Type IV is solid-rich inclusion, and Type V is a mixture of fluid and solid inclusion and daughter minerals. SEM-CL images show twin structure with growth texture, microphenocryst of spinel solid inclusions, massive and growth texture. Ruby and sapphire from Tanzania are distinctly distinguished by concentrations of Fe and Cr, and plotted in the particular field at $Al_{2}O_{3}/100-Cr_{2}O_{3}-Fe_{2}O_{3}$ diagram. According to FT-IR analysis, all corundum specimens from Tanzania showed the similar patterns, and absorption peaks of $455.09\~459.23\;cm^{-1},\;603.15\~611.71\;cm^{-1},\;1509.00\~1655.05\;cm^{-1}\;and\;3436.41\~3468.87\;cm^{-1}$. These distinctive characteristics mentioned above can be used to identify the locality and source of corundum stones from Tanzania.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.245-250
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• 2005

ZnO was deposited on sapphire single crystal substrate by an ultrasonic pyrolysis of Zinc Acetate Dehydrate (ZAH) with carrying Ar gas. Through Thermogravimetry-Differential Scanning Calorimetry(TG-DSC), zinc acetate dihydrate was identified to be dissolved into ZnO above $380^{\circ}C$. ZnO deposited at $380-700^{\circ}C$ showed polycrystalline structures with ZnO (101) and ZnO (002) diffraction peaks like bulk ZnO in XRD, and from which c-axis strain ${\Sigma}Z=0.2\%$ and compressive biaxial stress$\sigma=-0.907\;GPa$ was obtained for the ZnO deposited $400^{\circ}C$. Scanning electron microscope revealed that microstructures of the ZnO were dependent on the deposition temperature. ZnO grown below temperature $600^{\circ}C$ were aggregate consisting of zinc acetate and ZnO particles shaped with nanoblades. On the other hand the grain of the ZnO deposited at $700^{\circ}C$ showed a distorted hexagonal shape and was composed of many ultrafine ZnO powers of 10-25 nm in size. The formation of these ulrafine nm scale ZnO powers was explained by the model of random nucleation mechanism. The optical property of the ZnO was analyzed by the photoluminescence (PL) measurement.

• Progress in Superconductivity
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• v.13 no.2
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• pp.97-104
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• 2011

In the dielectric resonator method, which has been widely used for measuring the microwave surface resistance of superconductors, accuracies in the geometrical factors (G-factors) affect the uncertainty in the measured surface resistance. We compare the G-factors of short-ended sapphire resonator as obtained by using field analysis with those by using computer simulations: The former is obtained by using the analytic expressions for the electric and the magnetic field components inside the resonator, and the latter by using computer software. The G-factors as obtained by using the latter appear to be closer to those obtained by using the former as the resonator space is divided into larger number of sub-space, i.e., a tighter mesh, with a difference of ~8 % observed for a mesh of 14400 sub-spaces reduced to ~2 % for 114996 sub-spaces. Variations in the relative uncertainty in the surface resistance of typical $YBa_2Cu_3O_{7-\delta}$ superconductor films with those in the G-factors are studied, which provides an upper limit of the relative uncertainty in the G-factors required for realizing the target uncertainty in the surface resistance. These results could be useful in estimating the optimum number of meshes for obtaining the G-factors through computer simulations.

• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.339-344
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• 2011

The Ohmic contact of Ti/Au metals on n-type ZnO thin film deposited on c-plane sapphire substrates by pulsed laser deposition was investigated by TLM (transfer length method) patterns. The Ti/Au metal films with thickness of 35 nm and 90 nm were deposited by electron-beam evaporator and thermal evaporator, respectively. By using the photo-lithography method, the $100{\times}100{\mu}m^2$ TLM patterns with $6{\sim}61{\mu}m$ gaps were formed. To improve the electrical properties as well as to decrease an interface states and stress between metal and semiconductor, the post-annelaing process was done in oxygen ambient by rapid thermal annealing system at temperature of $100{\sim}500^{\circ}C$ for 1 min. In this study, it appeared that the minimum specific contact resistivity shows about $1.1{\times}10^{-4}{\Omega}{\cdot}cm^2$ in $300^{\circ}C$ annealed sample, which may be originated from formation of oxygen vacancies of ZnO during an oxidation of Ti metal at the interface of Ohmic contacts.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.420-420
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• 2013

We investigated oxygen plasma effect on defect states near the interface of AlGaN/GaN High Electron Mobility Transistor (HEMT) structure grown on a silicon substrate. After the plasma treatment, electrical properties were evaluated using a frequency dependant Capacitance-Voltage (C-V) and a temperature dependant C-V measurements, and a deep level transient spectroscopy (DLTS) method to study the change of defect densities. In the depth profile resulted from the temperature dependant C-V, a sudden decrease in the carrier concentration for two-dimensional electron gas (2DEG) nearby 250 K was observed. In C-V measurement, the interface states were improved in case of the oxygen-plasma treated samples, whereas the interface was degraded in case of the nitrogen-plasma treated sample. In the DLTS measurement, it was observed the two kinds of defects well known in AlGaN/GaN structure grown on sapphire substrate, which have the activation energies of 0.15 eV, 0.25 eV below the conduction band. We speculate that this defect state in AlGaN/GaN on the silicon substrate is caused from the decrease in 2DEG's carrier concentrations. We compared the various DLTS signals with filling pulse times to identify the characteristics of the newly found defect. In the filling pulse time range under the 80 us, the activation energies changed as the potential barrier model. On the other hand, in the filling pulse time range above the 80 us, the activation energies changed as the extended potential model. Therefore, we suggest that the found defect in the AlGaN/GaN/Si structure could be the extended defect related with AlGa/N/GaN interface states.