• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.605-611
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• 2014

$SrGd_{2-x}(MoO_4)_4:Er^{3+}/Yb^3$ phosphors with doping concentrations of $Er^{3+}$+ and $Yb^{3+}$ ($x=Er^{3+}+Yb^{3+}$, $Er^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) were successfully synthesized by the cyclic microwave-modified sol-gel method, and their upconversion mechanism and spectroscopic properties have been investigated in detail. Well-crystallized particles showed a fine and homogeneous morphology with grain sizes of $2-5{\mu}m$. Under excitation at 980 nm, $SrGd_{1.7}(MoO_4)_4:Er_{0.1}Yb_{0.2}$ and $SrGd_{1.5}(MoO_4)_4:Er_{0.05}Yb_{0.45}$ particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the domination of strong peaks at higher frequencies of 1023, 1092, and $1325cm^{-1}$ and at lower frequencies of 223, 2932, 365, 428, 538, and $594cm^{-1}$ induced by the incorporation of the $Er^{3+}$+ and $Yb^{3+}$+ elements into the $Gd^{3+}$ site in the crystal lattice, which resulted in the unit cell shrinkage accompanying a new phase formation of the $[MoO_4]^{2-}$ groups.

• Current Photovoltaic Research
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• v.2 no.1
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• pp.1-7
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• 2014

We developed a method of growing thin Si film at $600^{\circ}C$ by hot wire CVD using a very thin large-grained poly-Si seed layer for thin-film Si solar cells. The seed layer was prepared by crystallizing an amorphous Si film by vapor-induced crystallization using $AlCl_3$ vapor. The average grain size of the p-type epitaxial Si layer was about $20{\mu}m$ and crystallographic defects in the epitaxial layer were mainly low-angle grain boundaries and coincident-site lattice boundaries, which are special boundaries with less electrical activity. Moreover, with a decreasing in-situ boron doping time, the mis-orientation angle between grain boundaries and in-grain defects in epitaxial Si decreased. Due to fewer defects, the epitaxial Si film was high quality evidenced from Raman and TEM analysis. The highest mobility of $360cm^2/V{\cdot}s$ was achieved by decreasing the in-situ boron doping time. The performance of our preliminary thin-film solar cells with a single-side HIT structure and $CoSi_2$ back contact was poor. However, the result showed that the epitaxial Si film has considerable potential for improved performance with a reduced boron doping concentration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.35-36
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• 2009

In this work, we demonstrate 800V 4H-SiC power DMOSFETs with several structural alterations to obtain a low threshold voltage ($V_{TH}$) and a high figure of merit ($V_B^2/R_{SP,ON}$). To optimize the device performance, we consider four design parameters; (a) the doping concentration ($N_{CSL}$) of current spreading layer (CSL) beneath the p-base region, (b) the thickness of p-base ($t_{BASE}$), (c) the doping concentration ($N_J$) and width ($W_J$) of a JFET region, (d) the doping concentration ($N_{EPI}$) and thickness ($t_{EPI}$) of epi-layer. These parameters are optimized using 2D numerical simulation and the 4H-SiC DMOSFET structure results in a threshold voltage ($V_{TH}$) below ~3.8V, and high figure of merit ($V_B^2/R_{SP,ON}$>${\sim}200MW/cm^2$) for a power MOSFET in $V_B$-800V range.

• Current Photovoltaic Research
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• v.10 no.1
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• pp.16-22
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• 2022

The long-term stability of PSCs against visual and UV light, moisture, electrical bias and high temperature is an important issue for commercialization. In particular, since the operation temperature of solar cell can rise above 85℃, a study on thermal stability is required. In this study, the cause of thermal-induced degradation of PSCs was investigated using the SCAPS-1D simulation tool. First, PSCs of TiO₂/CH₃NH₃PbI₃/Spiro-OMeTAD/Au structure were exposed to a constant temperature of 85℃ to observe changes in conversion efficiency and quantum efficiency. Because the EQE reduction above 500 nm was remarkable, we simulated PSCs performance as a function of lifetime, doping density of perovskite and spiro-OMeTAD. Consequently, the main cause of thermal-induced degradation is considered to be the change in the perovskite doping concentration and lifetime due to ion migration of perovskite.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.4
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• pp.159-163
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• 2016

Up-conversion (UC) luminescence properties of polycrystalline $Er^{3+}/Yb^{3+}$ doped $NaGd(MoO_4)_2$ phosphors synthesized by a simple solid-state reaction method were investigated in detail. Used to 980 nm excitation (InfraRed area), $Er^{3+}/Yb^{3+}$ co-doped $NaGd(MoO_4)_2$ exhibited very weak red emissions near 650 and 670 nm, and very strong green UC emissions at 540 and 550 nm corresponding to the infra 4f transitions of $Er^{3+}(^4F_{9/2},\;^2H_{11/2},\;^4S_{3/2}){\rightarrow}Er^{3+}(^4I_{15/2})$. The optimum doping concentration of $Er^{3+}$, $Yb^{3+}$ for highest emission intensity was determined by XRD and PL analysis. The $Er^{3+}/Yb^{3+}$ (10.0/10.0 mol%) co-doped $NaGd(MoO_4)_2$ phosphor sample exhibited very strong shiny green emission. A possible UC mechanism for $Er^{3+}/Yb^{3+}$ co-doped $NaGd(MoO_4)_2$ depending on the pump power dependence was discussed.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.599-603
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• 2014

$NaLa_{1-x}(MoO_4)_2:Eu^{3+}/Yb^3$ phosphors with doping concentrations of $Eu^{3+}$ and $Yb^{3+}$ ($x= Eu^{3+}+Yb^{3+}$, $Eu^{3+}=0.05$, 0.1, 0.2 and $Yb^{3+}= 0.2$, 0.45) were successfully synthesized by the microwave-modified sol-gel method, and the upconversion and spectroscopic properties were investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, $NaLa_{0.5}(MoO_4)_2:Eu_{0.05}Yb_{0.45}$ particles exhibited a strong 525-nm emission band and a weak 550-nm emission band in the green region, and a very weak 665-nm emission band in the red region. The strong 525-nm emission in the green region corresponds to the $^7F_1{\rightarrow}^5D_1$ transition and the weak 550-nm emission in the green region corresponds to the $^7F_0{\rightarrow}^5D_2$ transition, while the very weak emission 665-nm band in the red region corresponds to the $^5D_0{\rightarrow}^7F_3$ transition. The Raman spectra of the doped particles indicated the domination of strong peaks at higher frequencies of 762, 890, 1358 and $1430cm^{-1}$ and weak peaks at lower frequencies of 323, 388 and $450cm^{-1}$ induced by the disorder of the $[MoO4]^{2-}$ groups with the incorporation of the $Eu^{3+}$ and $Yb^{3+}$ elements into the crystal lattice or by a new phase formation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.133-134
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• 2006

A simple doping method to fabricate a very thin channel body of the n-type fin field-effect-transistor (FinFET) with a 20 nm gate length by solid-phase-diffusion (SPD) process is presented. Using As-doped spin-on-glass as a diffusion source of arsenic and the rapid thermal annealing, the n-type source-drain extensions with a three-dimensional structure of the FinFET devices were doped. The junction properties of arsenic doped regions were investigated by using the $n^+$-p junction diodes which showed excellent electrical characteristics. Single channel and multi-channel n-type FinFET devices with a gate length of 20-100 nm was fabricated by As-SPD and revealed superior device scalability.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.5
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• pp.394-398
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• 2007

A simple doping method to fabricate a very thin channel body of the nano-scaled n-type fin field-effect-transistor (FinFET) by arsenic solid-Phase-diffusion (SPD) process is presented. Using the As-doped spin-on-glass films and the rapid thermal annealing for shallow junction, the n-type source-drain extensions with a three-dimensional structure of the FinFET devices were doped. The junction properties of arsenic doped regions were investigated by using the $n^+$-p junction diodes which showed excellent electrical characteristics. The n-type FinFET devices with a gate length of 20-100 nm were fabricated by As-SPD and revealed superior device scalability.

• Transactions on Electrical and Electronic Materials
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• v.18 no.6
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• pp.364-369
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• 2017

Double molybdate $NaGd_{1-x}(MoO_4)_2:Ho^{3+}/Yb^{3+}$ phosphors with proper doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0$ and 0.05, and $Yb^{3+}=0$, 0.35, 0.40, 0.45, and 0.50) were successfully synthesized using the microwave sol-gel method. Well-crystallized particles formed after heat-treatment at $800^{\circ}C$ for 16 h showed fine and homogeneous morphologies with particle sizes of $1{\sim}3{\mu}m$. The spectroscopic properties were examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the upconversion doped samples exhibited strong yellow emissions, from the combination of strong emission bands at 545 nm and 655 nm in the green and red spectral regions, respectively. The strong 545 nm emission band in the green region corresponded to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions, while the strong 655 nm band in the red region appeared because of the $^5F_5{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions. The pump power dependence and the Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.29-34
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• 2016

$NaLa_{1-x}{(MoO_4)}_2$:$Ho^{3+}/Yb^{3+}$ phosphors with the correct doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0.05$ and $Yb^{3+}=0.35$, 0.40, 0.45 and 0.50) were successfully synthesized by the microwave-modified sol-gel method. Well-crystallized particles formed after heat-treatment at $900^{\circ}C$ for 16 h showed a fine and homogeneous morphology with particle sizes of $3-5{\mu}m$. The optical properties were examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at 545-nm and 655-nm emission bands in green and red spectral regions, respectively. The strong 545-nm emission band in the green region corresponds to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition in $Ho^{3+}$ ions, while the strong emission 655-nm band in the red region appears due to the $^5F_5{\rightarrow}^5I_8$ transition in $Ho^{3+}$ ions. Pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.