• Journal of the Korean Society for Heat Treatment
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• v.28 no.1
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• pp.7-16
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• 2015

The fabrication of high quality graphene using chemical vapor deposition (CVD) method for application in semiconductor, display and transparent electrodes is investigated. Temperature and pressure have major impact on the growth of graphene. Graphene doping was obtained by deposition of $MoO_3$ thin films using thermal evaporator. Bilayer graphene and the metal layer graphene were obtained. According to the behavior of graphene growth P-type doping was confirmed. Graphene obtained through experiments was analyzed using optical microscopy, Raman spectroscopy, UV-visible light spectrophotometer, 4-point probe sheet resistance meter and atomic force microscopy.

• Current Photovoltaic Research
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• v.10 no.1
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• pp.23-27
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• 2022

In this study, we investigate organic-inorganic halide perovskite solar cells with a vacuum thermal evaporated hole transporting layer (NPB/MoO_3-x). By replacing solution process based Spiro-MeOTAD with vacuum thermal evaporation based NPB/MoO_3-x, a thin hole transporting layer was implemented. In addition, parasitic absorption that may occur during the doping process was eliminated by excluding solution process doping. In a solar cell with a thin vacuum thermal evaporated hole transporting layer, the short-circuit current density (Jsc) increased to 23.93 mA/cm², resulting in the highest power converstion efficiency (PCE) at 18.76%. Considering these results, it is essential to control the thickness of hole transporting layer located at the top in solar cell configuration.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1260_1261
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• 2009

A detailed investigation and structure of tested samples are clearly presented. As a reference, $Ge_1Se_1Te_2$/Sb only sample was also investigated. We used compound of Ge-Se-Te material for phase-change cell. Actually, the performance properties have been improved surprisingly then conventional Ge-Sb-Te. However, crystallization time was as long as ever for amorphization time. We conducted this esperiment in order to solve that problem by doping-Sb.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.98.2-98.2
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• 2007

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.1
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• pp.30-35
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• 2024

In order to improve the efficiency of the water splitting system for hydrogen production, the high overvoltage in the electrochemical reaction caused by the catalyst in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) must be reduced. Among them, transition metal-based compounds are attracting attention as catalyst materials that can replace precious metals such as platinum that are currently used. In this study, nickel foam, an inexpensive metal porous material, was used as a support, and Fe-doped β-Ni(OH)₂ microcrystals were synthesized through a hydrothermal synthesis process. In addition, in order to improve OER properties, changes in the shape, crystal structure, and water splitting characteristics of Fe-Mo co-doped β-Ni(OH)₂ microcrystals synthesized by co-doping with Mo were observed. The changes in the shape, crystal structure, and applicability as a catalyst for water splitting were examined.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.345-348
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• 2017

In this work, static characteristics of 4H-SiC SJ-ACCUFETs were obtained by adjusting the p-pillar region. The structure of this SJ-ACCUFET was designed by using a two-dimensional simulator. The static characteristics of SJ-ACCUFET, such as the breakdown voltages, on-resistance, and figure of merits, were obtained by varying the p-pillar doping concentration from $1{\times}10^{15}cm^{-3}$ to $5{\times}10^{16}cm^{-3}$ and the thickness from $0{\mu}m$ to $9{\mu}m$. The doping concentration and the thickness of p-pillar region are closely related to the break down voltage and on-resistance and threshold voltages. Hence a silicon carbide SJ-ACCUFET structure with highly intensified breakdown voltages and low on-resistances with good figure of merits can be achieved by optimizing the p-pillar thickness and doping concentration.

• 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.

• Applied Microscopy
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• v.47 no.1
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• pp.19-28
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• 2017

Since graphene was discovered in 2004, two-dimensional (2D) materials have been actively studied. Especially, 2D transition metal dichalcogenides (TMDs), such as $MoS_2$ and $WS_2$, have been the subject of significant research because of their exceptional optical, electrical, magnetic, catalytic, and morphological properties. Therefore, these materials are expected to be used in a variety of applications. Furthermore, tuning the properties of TMDs is essential to improve their performance and expand their applications. This review classifies the various doping methods of 2D TMDs, and it summarizes how the dopants interact with the materials and how the performance of the materials improves depending on the synthesis methods and the species of the dopants.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.564-569
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• 2018

$Cu_2ZnSn(S,Se)_4$ (CZTSSe) films were prepared on Mo coated soda lime glass substrates by sulfo-selenization of sputtered stacked Zn-Sn-Cu(CZT) precursor films. The precursor was dried in a capped state with aqueous NaOH solution. The CZT precursor films were sulfo-selenized in the S + Se vapor atmosphere. Sodium was doped during the sulfo-selenization treatment. The effect of sodium doping on the structural and electrical properties of the CZTSSe thin films were studied using FE-SEM(field-emission scanning electron microscopy), XRD(X-ray diffraction), XRF(X-ray fluorescence spectroscopy), dark current, SIMS(secondary ion mass spectrometry), conversion efficiency. The XRD, XRF, FE-SEM, Dark current, SIMS and cell efficiency results indicated that the properties of sulfo-selenized CZTSSe thin films were strongly related to the sodium doping. Further detailed analysis and discussion for effect of sodium doping on the properties CZTSSe thin films will be discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.10
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• pp.767-770
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• 2010

In this work, we investigated the static characteristics of 4H-SiC vertical metal-oxidesemiconductor field effect transistors (VMOSFETs) by adjusting the doping level of n-epilayer and the effect of a current spreading layer (CSL), which was inserted below the p-base region with highly doped n+ state ($5{\times}10^{17}cm^{-3}$). The structure of SiC VMOSFET was designed by using a 2-dimensional device simulator (ATLAS, Silvaco Inc.). By varying the n-epilayer doping concentration from $1{\times}10^{16}cm^{-3}$ to $1{\times}10^{17}cm^{-3}$, we investigated the static characteristics of SiC VMOSFETs such as blocking voltages and on-resistances. We found that CSL helps distribute the electron flow more uniformly, minimizing current crowding at the top of the drift region and reducing the drift layer resistance. For that reason, silicon carbide VMOSFET structures of highly intensified blocking voltages with good figures of merit can be achieved by adjusting CSL and doping level of n-epilayer.