• Journal of Powder Materials
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• v.26 no.3
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• pp.237-242
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• 2019

In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate ($NaNO_3$) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide ($TiO_2$) particles. The added $NaNO_3$ prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing $NaNO_3$ and NaF from the secondary particles, which consist of the salts and $TiO_2$ nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized $TiO_2$ nanoparticles have a size of approximately 2-10 nm a bandgap energy of 3.1-3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized $TiO_2$ nanoparticles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.576-581
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• 2023

The Ga₂O₃ thin films were deposited using an RF sputtering system and the effect of crystallographic and optical properties under rapid thermal annealing conditions on Ga₂O₃ thin film was evaluated. A rapid thermal annealing method can fabricate a crystalline Ga₂O₃ thin film which is applied to various fields with a low cost and a high efficiency compared with the conventional post-annealing method. In this study, the Ga₂O₃ treated at 900℃ for 1 min showed the beta and gamma phases in XRD measurement. In optical properties, the crystalline Ga₂O₃ represented a high transmittance of more than 80% in the visible region and was calculated with a high optical bandgap energy of 4.58 eV. The beta and gamma phases Ga₂O₃ can be obtained by adjusting the rapid thermal annealing temperatures, and the various properties such as the optical bandgap energy can be controlled. Moreover, it is expected that crystalline Ga₂O₃ can be applied to various devices by controlling not only temperature but process time.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.585-591
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• 2018

Characteristics of nano-structured $SiO_2:Zn$ hollow powders prepared in the micro drop fluidized reactor process were investigated with respect to bandgap energy and surface activity. The $SiO_2:Zn$ hollow powders were successfully prepared continuously in the one step process with reasonable production efficiency, with varying the amount of THAM (tris(hydroxymethyl)-aminomethane) additive and concentration of $Zn^{2+}$ ions. The doping of $Zn^{2+}$ ions into $SiO_2$ lattice led to the reduction of bandgap energy by forming the acceptor level of $Zn^{2+}$ below the conduction band of $Si^{4+}$ ions. The hollow shape also contributed to reduce the bandgap energy of $SiO_2:Zn$ powders. The doping of $Zn^{2+}$ ions into $SiO_2$ hollow powders could enhance the surface activity by forming SiO-H stretching and oxygen vacancies at the surface of $SiO_2:Zn$ powders.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.291.1-291.1
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• 2016

Graphene by one of the two-dimensional (2D) materials has been focused on electronic applications due to its ultrahigh carrier mobility, outstanding thermal conductivity and superior optical properties. Although graphene has many remarkable properties, graphene devices have low on/off current ratio due to its zero bandgap. Despite considerable efforts to open its bandgap, it's hard to obtain appropriate improvements. To solve this problem, heterojunction barristor was proposed based on graphene. Mostly, this heterojunction barristor is made by transition metal dichalcogenides (TMDs), such as molybdenum disulfide ($MoS_2$) and tungsten diselenide ($WSe_2$), which have extremely thickness scalability of TMDs. The heterojunction barristor has the advantage of controlling graphene's Fermi level by applying gate bias, resulting in barrier height modulation between graphene interface and semiconductor. However, charged impurities between graphene and $SiO_2$ cause unexpected p-type doping of graphene. The graphene's Fermi level modulation is expected to be reduced due to this p-doping effect. Charged impurities make carrier mobility in graphene reduced and modulation of graphene's Fermi level limited. In this paper, we investigated theoretically and experimentally a relevance between graphene's Fermi level and p-type doping. Theoretically, when Fermi level is placed at the Dirac point, larger graphene's Fermi level modulation was calculated between -20 V and +20 V of $V_{GS}$. On the contrary, graphene's Fermi level modulation was 0.11 eV when Fermi level is far away from the Dirac point in the same range. Then, we produced two types heterojunction barristors which made by p-type doped graphene and graphene treated 2.4% APTES, respectively. On/off current ratio (32-fold) of graphene treated 2.4% APTES was improved in comparison with p-type doped graphene.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.5
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• pp.294-300
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• 2017

$TeO_x$ thin films were deposited at various $O_2$/Ar gas-flow ratios by a reactive RFmagneton sputtering technique from $TeO_2$ and Te targets. X-ray diffraction (XRD) results revealed that the $TeO_x$ thin films were amorphous. The structure and chemical composition of the $TeO_x$ thin films were investigated by fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The optical characteristics of the $TeO_x$ thin films were investigated by an Ellipsometer and a UV-VIS-NIR spectrophotometer. According to the $O_2$/Ar gas-flow ratios, the atomic composition ratio of $TeO_x$ thin films was divided into two regions(x=1-2, 2-3). Different optical characteristics were shown in each region. With an increasing $O_2$/Ar gas-flow ratio, the refractive index of the $TeO_x$ thin films decreased and the optical bandgap of the films increased.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1280-1282
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• 1994

The method of passivation for protecting the $Hg_{l-x}Cd_xTe$ surface is important device fabrication process, because the surface components are highly reactive leading to its chemical and electrical instability. Especially, the material of which composition is x=0.2 or 0.3, is narrow bandgap semiconductor and used as detector of infrared radiation. The device performance of narrow bandgap semiconductors are largely governed by the properties of the semiconductor surface. The electro-chemical processing of $Hg_{l-x}Cd_xTe$ allows rigorous control of the surface chemistry and provides an in-situ monitor of surface reaction. So electro-chemical reduction at specific potential can selectively eliminate the undesirable species on the surface and manipulated to reproducibly attain the desired stoichiometry. This method shows to assess the quality or chemically treated $Hg_{l-x}Cd_xTe$ good surface.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.9
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• pp.1-6
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• 2000

Utilizing impurity free vacancy diffusion (IFVD) method, area selective intermixing of InGaAs/InGaAsP multi-quantum well (MQW) structure was done. After this, wavelength division demultiplexing waveguide type photodetectoers was integrated and measured. It showed large blue shift in bandgap due to intermixing of MQW. Photodetectors are based on typical p-i-n structure and devices having large and small bandgap areas line up linearly. Width of waveguide and length of each photodetector are 20 and 250 ${\mu}m$, respectively, TE/TM polarized light from tunable laser was butt-coupled to the photodetector and spectral response was measured. Photodetectors can demultiplexing 1480 and 1550 nm wavelength.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.204-204
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• 2009

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.20-22
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• 2003

본 논문에서는 Photonic Bandgap(PBG)를 공진 특성을 이용하여 마이크로파 발진기의 위상잡음을 줄이기 위한 기술을 제시한다. 마이크로스트립 라인으로 구현한 공진기는 낮은 Q(Quality factor)를 가진다. PBG를 적용했을 때 공진기의 Q값을 높여줌으로써 발진기의 위상잡음 특성이 향상됨을 보이고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2003.08a
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• pp.121-121
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• 2003