• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.308-310
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• 2022

Ultrawide bandgap gallium oxide (Ga₂O₃) semiconductors are known to have excellent photocatalytic properties due to their high redox potential. In this study, CO₂ reduction is demonstrated using nanostructured Ga₂O₃ photocatalyst under ultraviolet (254 nm) light source conditions. After the CO₂ reduction, C₂H₄ remained as a by-product in this work. Nanostructured Ga₂O₃ photocatalyst also showed an excellent endurance characteristic. Photogenerated electron-hole pairs boosted the CO₂ reduction to C₂H₄ via nanostructured Ga₂O₃ photocatalyst, which is attributed to the ultrawide and almost direct bandgap characteristics of the gallium oxide semiconductor. The findings in this work could expedite the realization of CO₂ reduction and a simultaneous C₂H₄ production using a low cost and high performance photocatalyst.

• Applied Science and Convergence Technology
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• v.24 no.5
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• pp.151-155
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• 2015

The interfacial electronic structure between zinc phthalocyanine (ZnPc) and aluminumdoped zinc oxide (AZO) substrates has been evaluated by ultraviolet photoemission spectroscopy and angle-dependent x-ray absorption spectroscopy to understanding the molecular orientation of a ZnPc layer on the performance of small molecule organic photovoltaics (OPVs). We find that the ZnPc tilt angle improves the ${\pi}-{\pi}$ interaction on the AZO substrate, thus leading to an improved short-circuit current in OPVs based on phthalocyanine. Furthermore, the molecular orientation-dependent energy level alignment has been analyzed in detail using ultraviolet photoemission spectroscopy. We also obtained complete energy level diagrams of ZnPc/AZO and ZnPc/indium thin oxide.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.77-78
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• 2006

We fabricated photonic crystals on GaAs and GaN substrates. After anodizing the aluminium thin film in electrochemical embient, the porous alumina was implemented to the mask for reactive ion beam etching process of GaAs wafer. And photonic crystals in GaN wafer were also fabricated using electron beam nano-lithography process. The coated PMMA thin film with 200 nm-thickness on GaN surface was patterned with triangular lattice and etched out the GaN surface by the inductively coupled plasma source. The fabricated GaAs and GaN photonic crystals provide the enhanced intensities of light emission for the wavelengths of 858 and 450 nm, respectively. We will present the detailed dimensions of photonic crystals from SEM and AFM measurements.

• Journal of Sensor Science and Technology
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• v.31 no.4
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• pp.187-193
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• 2022

The accurate detection of environmental and biomarker gas species has attracted increasing attention due to their broad applications, such as air quality monitoring, disease diagnosis, and explosive chemicals detection. To accurately detect target gas species using chemiresistive gas sensors, using nanocatalysts on semiconducting metal oxides (SMOs) is considered the most promising approach. This review summarizes recent studies on methods for nanocatalysts functionalization on SMOs to achieve the highly selective gas sensors. To this end, we discuss various nanocatalyst decorated metal oxide-based chemiresistive gas sensors and provide an insight to construct highly accurate gas sensors.

• Journal of Powder Materials
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• v.31 no.4
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• pp.336-341
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• 2024

Molybdenum, valued for its high melting point and exceptional physical and chemical properties, is studied in diverse fields such as electronics, petrochemicals, and aviation. Among molybdenum oxides, molybdenum dioxide stands out for its higher electrical conductivity than other transition metal oxides due to its structural characteristics, exhibiting metallic properties. It is applied as pellets to gas sensors, semiconductors, and secondary batteries for its properties. Thus, research on molybdenum dioxide compaction and pressureless sintering is necessary, yet research on pressureless sintering is currently insufficient. This study synthesized MoO₃ powder via solution combustion synthesis and reduced it using the 3% hydrogen/argon gas mixture to investigate the effect of reduction temperature on the powder. Additionally, the reduced powder was compacted and subjected to pressureless sintering with temperature as a variable. The density and the microstructure of brown parts were analyzed and discussed.

• Journal of Sensor Science and Technology
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• v.29 no.6
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• pp.407-411
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• 2020

In this study, we propose an array-type gas sensor with high selectivity and response using multiple oxide semiconductors. The sensor array was composed of SnO₂ and In₂O₃, and the detection characteristics were improved by using Pt, Au, and Pd catalysts. All samples were deposited directly on the Pt interdigitated electrode (IDE) through the e-beam evaporator glancing angle deposition (GAD) method. They grew in the form of well-aligned nanorods at off-axis angles. The prepared SnO₂ and In₂O₃ nanorod samples were exposed to CH₃COCH₃, C₇H₈, and NO₂ gases in a 300℃ dry condition. Au-decorated SnO₂, Au-decorated In₂O₃, and Pd-decorated In₂O₃ exhibited high selectivity for CH₃COCH₃, C₇H₈, and NO₂, respectively. They demonstrated a high detection limit of the sub ppb level computationally. In addition, measurements from each sensor were executed in the 40% relative humidity condition. Although there was a slight reduction in detection response, high selectivity and distinguishable detection characteristics were confirmed.

• Journal of Sensor Science and Technology
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• v.30 no.5
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• pp.309-313
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• 2021

Organic semiconductors have received tremendous attention for their research because of their tunable electrical and optical properties that can be achieved by changing their molecular structure. However, organic materials are inherently unstable in the presence of oxygen and moisture. Therefore, it is necessary to develop moisture and air stable semiconducting materials that can replace conventional organic semiconductors. In this study, we developed a NiO_x thin film through a solution process. The electrical characteristics of the NiO_x thin film, depending on the thermal annealing temperature and UV-ozone treatment, were determined by applying them to the hole injection layer of an organic light-emitting diode. A high annealing temperature of 500 ℃ and UV-ozone treatment enhanced the conductivity of the NiO_x thin films. The optimized NiO_x exhibited beneficial hole injection properties comparable those of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN), a conventional organic hole injection layer. As a result, both devices exhibited similar power efficiencies and the comparable electroluminescent spectra. We believe that NiO_x could be a potential solution which can provide robustness to conventional organic semiconductors.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.497-497
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• 2013

Semiconducting amorphous InGaZnO (a-IGZO) has attracted significant research attention as improved deposition techniques have made it possible to make high-quality a-IGZO thin films. IGZO thin films have several advantages over thin film transistors (TFTs) based on other semiconducting channel layers.The electron mobility in IGZO devices is relatively high, exceeding amorphous Si (a-Si) by a factor of 10 and most organic devices by a factor of $10^2$. Moreover, in contrast to other amorphous semiconductors, highly conducting degenerate states can be obtained with IGZO through doping, yet such a state cannot be produced with a-Si. IGZO thin films are capable of mobilities greaterthan 10 $cm^2$/Vs (higher than a-Si:H), and are transparent at visible wavelengths. For oxide semiconductors, carrier concentrations can be controlled through oxygen vacancy concentration. Hence, adjusting the oxygen partial pressure during deposition and post-deposition processing provides an effective method of controlling oxygen concentration. In this study, we deposited IGZO thinfilms at optimized conditions and then analyzed the film's electrical properties, surface morphology, and crystal structure. Then, we explored how to generate IGZO thin films using DC magnetron sputtering. We also describe the construction and characteristics of a bottom-gate-type TFT, including the output and transfer curves and bias stress instability mechanism.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.164-164
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• 2010

The impurity doped ZnO has been extensively studied because of its optoelectric properties. GIZO (Ga-In-Zn-O) amorphous oxide semiconductors has been widely used as transparent flexible semiconductor material. Recently, various amorphous transparent semiconductors such as IZO (In-Zn-O), GIZO, and HIZO (Hf-In-Zn-O) were developed. In this work, we examined the local structures of IZO, GIZO, and HIZO. The local coordination structure was investigated by the extended X-ray absorption fine structure. The IZO, GIZO and HIZO thin films ware deposited on the glass substrate with thickness of 400nm by the radio frequency sputtering method. The targets were prepared by the mixture of $In_2O_3$, ZnO and $HfO_2$ powders. The percent ratio of In:Zn in IZO, Ga:In:Zn in GIZO and Hf:In:Zn in HIZO was 45:55, 33:33:33 and 10:35:55, respectively. In this work, we found that IZO, GIZO and HIZO are all amorphous and have a similar local structure. Also, we obtained the bond distances of $d_{Ga-O}=1.85\;{\AA}$, $d_{Zn-O}=1.98\;{\AA}$, $d_{Hf-O}=2.08\;{\AA}$, $d_{In-O}=2.13\;{\AA}$.

• Journal of Sensor Science and Technology
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• v.28 no.6
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• pp.377-384
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• 2019

People currently spend more than 80% of their time indoors; therefore, the management of indoor air quality has become an important issue. The contamination of indoor air can cause sick house syndrome and various environmental diseases such as atopy and nephropathy. Formaldehyde gas, which is the main contaminant of indoor air, is lethal even with microscopic exposure; however, it is commonly used as an adhesive and waterproofing agent for indoor building materials. Therefore, there is a need for a gas sensor capable of detecting trace amounts of formaldehyde gas. In this review, we summarize recent studies on metal oxide-based semiconductor gas sensors for formaldehyde gas detection, methods to improve the gas-sensing properties of metal oxides of various dimensions, and the effects of catalysts for the detection of parts-per-billion level gases. Through this, we discuss the necessary characteristics of the metal oxidebased semiconductors for gas sensors for the development of next-generation sensors.