• Korean Journal of Materials Research
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• v.29 no.1
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• pp.1-6
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• 2019

Recent industrialization has led to a high demand for the use of fossil fuels. Therefore, the need for producing hydrogen and its utilization is essential for a sustainable society. For an eco-friendly future technology, photoelectrochemical water splitting using solar energy has proven promising amongst many other candidates. With this technique, semiconductors can be used as photocatalysts to generate electrons by light absorption, resulting in the reduction of hydrogen ions. The photocatalysts must be chemically stable, economically inexpensive and be able to utilize a wide range of light. From this perspective, cuprous oxide($Cu_2O$) is a promising p-type semiconductor because of its appropriate band gap. However, a major hindrance to the use of $Cu_2O$ is its instability at the potential in which hydrogen ion is reduced. In this study, gold is used as a bottom electrode during electrodeposition to obtain a preferential growth along the (111) plane of $Cu_2O$ while imperfections of the $Cu_2O$ thin films are removed. This study investigates the photoelectrochemical properties of $Cu_2O$. However, severe photo-induced corrosion impedes the use of $Cu_2O$ as a photoelectrode. Two candidates, $TiO_2$ and $SnO_2$, are selected for the passivation layer on $Cu_2O$ by by considering the Pourbaix-diagram. $TiO_2$ and $SnO_2$ passivation layers are deposited by atomic layer deposition(ALD) and a sputtering process, respectively. The investigation of the photoelectrochemical properties confirmed that $SnO_2$ is a good passivation layer for $Cu_2O$.

• Journal of radiological science and technology
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• v.43 no.6
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• pp.481-487
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• 2020

Radiation measurement technology has steadily improved and its usage is expanding in various industries such as nuclear medicine, security search, satellite, nondestructive testing, environmental industries and the domain of nuclear power plants (NPPs). Especially, the simultaneous measurements of gamma rays and neutrons can be even more critical for nuclear safety management of spent nuclear fuel and monitoring of the nuclear material. A semiconductor detector comprising cadmium, zinc, and tellurium (CZT) enables to detect gamma-rays due to the significant atomic weight of the elements via immediate neutron and gamma-ray detection. Semiconductor sensors might be used for nuclear safety management by monitoring nuclear materials and spent nuclear fuel with high spatial resolution as well as providing real-time measurements. We aim to introduce a portable nuclide-analysis device that enables the simultaneous measurements of neutrons and gamma rays using a CZT sensor. The detector has a high density and wide energy band gap, and thus exhibits highly sensitive physical characteristics and characteristics are required for performing neutron and gamma-ray detection. Portable nuclide-analysis device is used on NPP-decommissioning sites or the purpose of nuclear nonproliferation, it will rapidly detect the nuclear material and provide radioactive-material information. Eventually, portable nuclide-analysis device can reduce measurement time and economic costs by providing a basis for rational decision making.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.101-106
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• 2022

In this paper, WBG semiconductor such as SiC and GaN were applied as power switches for LCL circuit that can be applied to satellite power systems and the test results of the LCL circuit are reported. P-channel MOSFET and N-channel MOSFET, which were generally used in the conventional LCL circuit, were applied together to expand the utility of the test results. The design and stability evaluation were performed using a Micro Cap circuit simulation program. For the test circuit, a module using each switch was manufactured, and a total of 5 modules were manufactured and the steady state and transient state characteristics were compared. From the experimental results, the LCL circuit for power supply of the satellite power system constructed in this paper satisfied the constant current and constant voltage conditions under various operating conditions. The P-channel MOSFET showed the lowest efficiency characteristics, and the three N-channel switches of Si, SiC and GaN showed relatively high efficiency characteristics of up to 99.05% or more. In conclusion, it was verified that the on-resistor of the switch had a direct effect on the efficiency and loss characteristics.

• Journal of IKEEE
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• v.26 no.4
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• pp.537-544
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• 2022

This paper analyzes the occurrence and cause of bond wires fusing used in the manufacture of pulsed high power amplifiers. Recently GaN HEMT has been spotlight in the fields of electronic warfare, radar, base station and satellite communication. In order to produce the maximum output power, which is the main performance of the high-power amplifier, optimal impedance matching is required. And the material, diameter and number of bond wires must be determined in consideration of not only the rated current but also the heat generated by the transient current. In particular, it was confirmed that compound semiconductor with a wide energy band gap such as GaN trigger fusing of the bond wire due to an increase in thermal resistance when the design efficiency is low or the heat dissipation is insufficient. This data has been simulated for exothermic conditions, and it is expected to be used as a reference for applications using GaN devices as verified through IR microscope.

• Journal of IKEEE
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• v.26 no.4
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• pp.553-559
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• 2022

In this paper, RC snubber circuit design technology for oscillation suppression in half-bridge configuration of cascode gallium nitride (GaN) field effect transistors (FETs) is analyzed. A typical wide band-gap (WBG) device, cascode GaN FET, has excellent high-speed switching characteristics. However, due to such high-speed switching characteristics, a false turn-off problem is caused, and an RC snubber circuit is essential to suppress this. In this paper, the commonly used experimental-based RC snubber design technique and the RC snubber design technique using the root locus method are compared and analyzed. In the general method, continuous circuit changes are required until the oscillation suppression performance requirement is met based on experimental experience . However, in root locus method, the initial value can be set based on the non-oscillation R-C map. To compare the performance of the two aforementioned design methods, a simulation experiment and a switching experiment using an actual double pulse circuit are performed.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.3
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• pp.59-68
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• 2023

Currently, yellow phosphor of Y3Al5O12:Ce3+ (YAG:Ce) fluorescent material is applied to a 450~480nm blue LED light source to implement a white LED device and it has a simple structure, can obtain sufficient luminance, and is economical. However, in this method, in terms of spectrum analysis, it is difficult to mass-produce white LEDs having the same color coordinates due to color separation cause by the wide wavelength gap between blue and yellow band. There is a disadvantage that it is difficult to control optical properties such as color stability and color rendering. In addition, this method does not emit purple light in the range of 380 to 420nm, so it is white without purple color that can not implement the spectrum of the entire visible light spectrum as like sunlight. Because of this, it is difficult to implement a color rendering index(CRI) of 90 or higher, and natural light characteristics such as sunlight can not be expected. For this, need for a method of implementing sunlight with one LED by using a method of combining phosphors with one light source, rather than a method of combining red, blue, and yellow LEDs. Using this method, the characteristics of an artificial sunlight LED device with a spectrum similar to that of sunlight were demonstrated by implementing LED devices of various color temperatures with high color rendering by injecting phosphors into a 405nm deep blue LED light source. In order to find the spectrum closest to sunlight, different combinations of phosphors were repeatedly fabricated and tested. In addition, reliability and mass productivity were verified through temperature and humidity tests and ink penetration tests.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.491-496
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• 2023

As the demand for p-type semiconductors increases, much effort is being put into developing new p-type materials. This demand has led to the development of novel new p-type semiconductors that go beyond existing p-type semiconductors. Copper iodide (CuI) has recently received much attention due to its wide band gap, excellent optical and electrical properties, and low temperature synthesis. However, there are limits to its use as a semiconductor material for thin film transistor devices due to the uncontrolled generation of copper vacancies and excessive hole doping. In this work, p-type CuI semiconductors were fabricated using the chemical vapor deposition (CVD) process for thin-film transistor (TFT) applications. The vacuum process has advantages over conventional solution processes, including conformal coating, large area uniformity, easy thickness control and so on. CuI thin films were fabricated at various deposition temperatures from 150 to 250 ℃ The surface roughness root mean square (RMS) value, which is related to carrier transport, decreases with increasing deposition temperature. Hall effect measurements showed that all fabricated CuI films had p-type behavior and that the Hall mobility decreased with increasing deposition temperature. The CuI TFTs showed no clear on/off because of the high concentration of carriers. By adopting a Zn capping layer, carrier concentrations decreased, leading to clear on and off behavior. Finally, stability tests of the PBS and NBS showed a threshold voltage shift within ±1 V.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.293-293
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• 2014

Over last decade InGaN alloy structures have become the one of the most promising materials among the numerous compound semiconductors for high efficiency light sources because of their direct band-gap and a wide spectral region (ultraviolet to infrared). The primary cause for the high quantum efficiency of the InGaN alloy in spite of high threading dislocation density caused by lattice misfit between GaN and sapphire substrate and severe built-in electric field of a few MV/cm due to the spontaneous and piezoelectric polarizations is generally known as the strong exciton localization trapped by lattice-parameter-scale In-N clusters in the random InGaN alloy. Nonetheless, violet-emitting (390 nm) conventional low-In-content InGaN/GaN multi-quantum wells (MQWs) show the degradation in internal quantum efficiency compared to blue-emitting (450 nm) MQWs owing higher In-content due to the less localization of carrier and the smaller band offset. We expected that an improvement of internal quantum efficiency in the violet region can be achieved by replacing the conventional low-In-content InGaN/GaN MQWs with ultra-thin, high-In-content (UTHI) InGaN/GaN MQWs because of better localization of carriers and smaller quantum-confined Stark effect (QCSE). We successfully obtain the UTHI InGaN/GaN MQWs grown via employing the GI technique by using the metal-organic chemical vapor deposition. In this work, 1 the optical and structural properties of the violet-light-emitting UTHI InGaN/GaN MQWs grown by employing the GI technique in comparison with conventional low-In-content InGaN/GaN MQWs were investigated. Stronger localization of carriers and smaller QCSE were observed in UTHI MQWs as a result of enlarged potential fluctuation and thinner QW thickness compared to those in conventional low-In-content MQWs. We hope that these strong carrier localization and reduced QCSE can turn the UTHI InGaN/GaN MQWs into an attractive candidate for high efficient violet emitter. Detailed structural and optical characteristics of UTHI InGaN/GaN MQWs compared to the conventional InGaN/GaN MQWs will be given.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.603-609
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• 2022

Passivation quality is mainly governed by epitaxial growth of crystalline silicon wafer surface. Void-rich intrinsic a-Si:H interfacial layer could offer higher resistivity of the c-Si surface and hence a better device efficiency as well. To reduce the resistivity of the contact area, a modification of void-rich intrinsic layer of a-Si:H towards more ordered state with a higher density is adopted by adapting its thickness and reducing its series resistance significantly, but it slightly decreases passivation quality. Higher resistance is not dominated by asymmetric effects like different band offsets for electrons or holes. In this study, multilayer of intrinsic a-Si:H layers were used. The first one with a void-rich was a-Si:H(I₁) and the next one a-SiO_x:H(I₂) were used, where a-SiO_x:H(I₂) had relatively larger band gap of ~2.07 eV than that of a-Si:H (I₁). Using a-SiO_x:H as I₂ layer was expected to increase transparency, which could lead to an easy carrier transport. Also, higher implied voltage than the conventional structure was expected. This means that the a-SiO_x:H could be a promising material for a high-quality passivation of c-Si. In addition, the i-a-SiO_x:H microstructure can help the carrier transportation through tunneling and thermal emission.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.275-281
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• 2017

AlN is a promising material for wide band gap and high-frequency electronics device due to its wide bandgap and high thermal conductivity. AlN has advantages as materials for power semiconductors with a larger breakdown field, and a smaller specific on-resistance at high voltage. The growth of a p-type AlN epilayer with high conductivity is important for a manufacturing an AlN-based applications. In this paper, Mg doped AlN epilayers were grown by a mixed-source HVPE. Al and Mg mixture were used as source materials for the growth of Mg-doped AlN epilayers. Mg concentration in the AlN was controlled by modulating the quantity of Mg source in the mixed-source. Surface morphology and crystalline structure of AlN epilayers with different Mg concentrations were characterized by FE-SEM and HR-XRD. XPS spectra of the Mg-doped AlN epilayers demonstrated that Mg was doped successfully into the AlN epilayer by the mixed-source HVPE.