• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.84-84
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• 2008

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.4
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• pp.285-296
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• 2005

Reduced pressure chemical vapor deposition technology has been used to study SiGe heterostructure epitaxy and device issues, including SiGe relaxed buffers, proper control of Ge component and crystalline defects, two dimensional delta doping, and their influence on electrical properties of devices. From experiments, 2D profiles of B and P presented FWHM of 5 nm and 20 nm, respectively, and doses in 5×10/sup 11/ ∼ 3×10/sup 14/ ㎝/sup -2/ range. The results could be employed to fabricate SiGe/Si heterostructure field effect transistors with both Schottky contact and MOS structure for gate electrodes. I-V characteristics of 2D P-doped HFETs revealed normal behavior except the detrimental effect of crystalline defects created at SiGe/Si interfaces due to stress relaxation. On the contrary, sharp B-doping technology resulted in significant improvement in DC performance by 20-30 ％ in transconductance and short channel effect of SiGe HMOS. High peak concentration and mobility in 2D-doped SiGe heterostructures accompanied by remarkable improvements of electrical property illustrate feasible use for nano-sale FETs and integrated circuits for radio frequency wireless communication in particular.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.145-149
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• 2016

$(Bi_{1/2}Na_{1/2})_{0.94}Ba_{0.06}(Ti_{1-x}Nb_x)O_3$ (BNBTxNb) ceramics were investigated in terms of the crystal structure as well as the ferroelectric, dielectric, and piezoelectric properties. While little change was observed in the microstructure except for a slight decrease in the average grain size, a significant change was noticed in the temperature dependence of dielectric and piezoelectric properties. It was shown that the property changes are closely related to the downward shift in the position of the ferroelectric-to-relaxor transition temperature with increasing amount of Nb doping. A special emphasis is put on the fact that Nb doping is so effective at decreasing the ferroelectric-to-relaxor transition temperature that even at no more than 2 at.% Nb addition, the transition temperature was already brought down slightly below room temperature, resulting in the birth of a large strain at 0.46 %, equivalent to $S_{max}/E_{max}=767pm/V$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.12
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• pp.2939-2945
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• 2014

This paper has analyzed the change of threshold voltage for oxide structure of symmetric and asymmetric double gate(DG) MOSFET. The asymmetric DGMOSFET can be fabricated with different top and bottom gate oxide thickness, while the symmetric DGMOSFET has the same top and bottom gate oxide thickness. Therefore optimum threshold voltage is considered for top and bottom gate oxide thickness of asymmetric DGMOSFET, compared with the threshold voltage of symmetric DGMOSFET. To obtain the threshold voltage, the analytical potential distribution is derived from Possion's equation, and Gaussian distribution function is used as doping profile. We investigate for bottom gate voltage, channel length and thickness, and doping concentration how top and bottom gate oxide thickness influences on threshold voltage using this threshold voltage model. As a result, threshold voltage is greatly changed for oxide thickness, and we know the changing trend greatly differs with bottom gate voltage, channel length and thickness, and doping concentration.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.36-41
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• 2014

Temperature dependence of magnetic moment (m-T) and the magnetization (M-H) at 5 K and 20 K of the in situ processed $MgB_2$ bulk pellets with/without carbon (C) doping were examined. The superconducting critical temperature ($T_c$), the superconducting transition width (${\delta}T$) and the critical current density ($J_c$) were estimated for ten test samples taken from the $MgB_2$ bulk pellets. The reliable m-T characteristics associated with the uniform $MgB_2$ formation were obtained for both $MgB_2$ pellets. The $T_cs$ and ${\delta}Ts$ of all test samples of the undoped $MgB_2$ were the same each other as 37.5 K and 1.5 K, respectively. The $T_cs$ and ${\delta}Ts$ of the C-doped $MgB_2$ were 36.5 K and 2.5 K, respectively. Unlike the m-T characteristics, there existed the difference among the M-H curves of the test samples, which might be caused by the microstructure variation. In spite of the slight $T_c$ decrease, the C doping was effective in enhancing the $J_c$ at 5 K.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.401-406
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• 2015

The change of subthreshold swing for channel length of asymmetric double gate(DG) MOSFET has been analyzed. The subthreshold swing is the important factor to determine digital chracteristics of transistor and is degraded with reduction of channel. The subthreshold swing for channel length of the DGMOSFET developed to solve this problem is investigated for channel thickness, oxide thickness, top and bottom gate voltage and doping concentration. Especially the subthreshold swing for asymmetric DGMOSFET to be able to be fabricated with different top and bottom gate structure is investigated in detail for bottom gate voltage and bottom oxide thickness. To obtain the analytical subthreshold swing, the analytical potential distribution is derived from Possion's equation, and Gaussian distribution function is used as doping profile. As a result, subthreshold swing is sensitively changed according to top and bottom gate voltage, channel doping concentration and channel dimension.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.05a
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• pp.755-758
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• 2014

This paper has analyzed the change of threshold voltage for oxide structure of symmetric and asymmetric double gate(DG) MOSFET. The asymmetric DGMOSFET can be fabricated with different top and bottom gate oxide thickness, while the symmetric DGMOSFET has the same top and bottom gate oxide thickness. Therefore optimum threshold voltage is considered for top and bottom gate oxide thickness of asymmetric DGMOSFET, compared with the threshold voltage of symmetric DGMOSFET. To obtain the threshold voltage, the analytical potential distribution is derived from Possion's equation, and Gaussian distribution function is used as doping profile. We investigate for bottom gate voltage, channel length and thickness, and doping concentration how top and bottom gate oxide thickness influences on threshold voltage using this threshold voltage model. As a result, threshold voltage is greatly changed for oxide thickness, and we know the changing trend very differs with bottom gate voltage, channel length and thickness, and doping concentration.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.3
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• pp.209-213
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• 2019

Recently, demand for high energy density and long cycling stability of energy storage system has increased for application using with frequency regulation (F/R) in power grid. Supercapacitor have long lifetime and high charge and discharge rate, it is very adaptable to apply a frequency regulation in power grid. Supercapacitor can complement batteries to reduce the size and installation of batteries. Because their utilization in a system can potentially eliminate the need for short-term frequent replacement as required by batteries, hence, saving the resources invested in the upkeep of the whole system or extension of lifecycle of batteries in the long run of power grid. However, low energy density in supercapacitor is critical weakness to utilization for huge energy storage system of power grid. So, it is still far from being able to replace batteries and struggle in meeting the demand for a high energy density. But, today, LIC (Lithium Ion Capacitor) considered as an attractive structure to improve energy density much more than EDLC (Electric double layer capacitor) because LIC has high voltage range up to 3.8 V. But, many aspects of the electrochemical performance of LIC still need to be examined closely in order to apply for commercial use. In this study, in order to improve the capacitance of LIC related with energy density, we designed new method of pre-doping in anode electrode. The electrode in cathode were fabricated in dry room which has a relative humidity under 0.1% and constant electrode thickness over $100{\mu}m$ was manufactured for stable mechanical strength and anode doping. To minimize of contact resistance, fabricated electrode was conducted hot compression process from room temperature to $65^{\circ}C$. We designed various pre-doping method for LIC structure and analyzing the doping mechanism issues. Finally, we suggest new pre-doping method to improve the capacitance and electrochemical stability for LIC.

• Journal of Environmental Science International
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• v.18 no.11
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• pp.1215-1224
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• 2009

This study evaluated the applicability of visible-light-driven N- and S-doped titanium dioxide($TiO_2$) for the control of low-level dimethyl sulfide(DMS) and dimethyl disulfide(DMDS). In addition, a photocatalytic unit(PU)-adsorption hybrid was evaluated in order to examine the removal of DMS and DMDS which exited the PU and a gaseous photocatalytic byproduct($SO_2$) which was generated during the photocatalytic processes. Fourier-Tranform-Infrared(FTIR) spectrum exhibited different surface characteristics among the three-types of catalysts. For the N- and S-doped $TiO_2$ powders, a shift of the absorbance spectrum towards the visible-light region was observed. The absorption edge for both the N- and S-doped $TiO_2$ was shifted to $\lambda$ 720 nm. The N-doped $TiO_2$ was superior to the S-doped $TiO_2$ in regards to DMS degradation. Under low input concentration(IC) conditions(0.039 and 0.027 ppm for DMS and DMDS, respectively), the N-doped $TiO_2$ revealed a high DMS removal efficiency(above 95%), but a gradual decreasing removal efficiency under high IC conditions(7.8 and 5.4 ppm for DMS and DMDS, respectively). Although the hybrid system exhibited a superior characteristic to PU alone regarding the removal efficiencies of both DMS and DMDS, this capability decreased during the course of a photocatalytic process under the high IC conditions. The present study identified the generation of sulfate ion on the catalyst surface and sulfur dioxide(maximum concentrations of 0.0019 and 0.0074 ppm for the photocatalytic processes of DMS and DMDS, respectively) in effluent gas of PU. However, this generation of $TiO_2$ would be an insignificant addition to indoor air quality levels.