• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.308-309
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• 2012

One of the critical issues in the growth of multijunction solar cell is the formation of a highly doped Esaki interband tunnel diode which interconnects unit cells of different energy band gap. Small electrical and optical losses are the requirements of such tunnel diodes [1]. To satisfy these requirements, tens of nanometer thick gallium arsenide (GaAs) can be a proper candidate due to its high carrier concentration in low energy band gap. To obtain highly doped GaAs in molecular beam epitaxy, the temperatures of Si Knudsen cell (K-cell) for n-type GaAs and Be K-cell for p-type GaAs were controlled during GaAs epitaxial growth, and the growth rate is set to 1.75 A/s. As a result, the doping concentration of p-type and n-type GaAs increased up to $4.7{\times}10^{19}cm^{-3}$ and $6.2{\times}10^{18}cm^{-3}$, respectively. However, the obtained n-type doping concentration is not sufficient to form a properly operating tunnel diode which requires a doping concentration close to $1.0{\times}10^{19}cm^{-3}$ [2]. To enhance the n-type doping concentration, n-doped GaAs samples were grown with a lower growth rate ranging from 0.318 to 1.123 A/s at a Si K-cell temperature of $1,180^{\circ}C$. As shown in Fig. 1, the n-type doping concentration was increased to $7.7{\times}10^{18}cm^{-3}$ when the growth rate was decreased to 0.318 A/s. The p-type doping concentration also increased to $4.1{\times}10^{19}cm^{-3}$ with the decrease of growth rate to 0.318 A/s. Additionally, bulk resistance was also decreased in both the grown samples. However, a transmission line measurement performed on the n-type GaAs sample grown at the rate of 0.318 A/s showed an increased specific contact resistance of $6.62{\times}10^{-4}{\Omega}{\cdot}cm^{-2}$. This high value of contact resistance is not suitable for forming contacts and interfaces. The increased resistance is attributed to the excessively incorporated dopant during low growth rate. Further studies need to be carried out to evaluate the effect of excess dopants on the operation of tunnel diode.

• Current Photovoltaic Research
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• v.4 no.2
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• pp.31-41
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• 2016

n-type PERT (passivated emitter, rear totally diffused) bifacial solar cells with boron and phosphorus diffusion as p+ emitter and n+ BSF (back surface field) have attracted significant research interest recently. In this work, the influences of wafer thickness, bulk lifetime, emitter, BSF on the photovoltaic characteristics of solar cells are discussed. The performance of the solar cell is determined by using one-dimensional solar cell simulation software PC1D. The simulation results show that the key role of the BSF is to decrease the surface doping concentration reducing the recombination and thus, increasing the cell efficiency. A lightly phosphorus doped BSF (LD BSF) was experimentally optimized to get low surface dopant concentration for n type bifacial solar cells. Pre-oxidation combined with a multi-plateau drive-in, using limited source diffusion was carried out before pre-deposition. It could reduce the surface dopant concentration with minimal impact on the sheet resistance.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.2
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• pp.76-81
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• 2007

Threshold voltage ($V_{th}$) modeling of doublegate (DG) MOSFETs was performed, for the first time, by considering barrier lowering in the short channel devices. As the gate length of DG MOSFETs scales down, the overlapped charge-sharing length ($x_h$) in the channel which is related to the barrier lowering becomes very important. A fitting parameter ${\delta}_w$ was introduced semi-empirically with the fin body width and body doping concentration for higher accuracy. The $V_{th}$ model predicted well the $V_{th}$ behavior with fin body thickness, body doping concentration, and gate length. Our compact model makes an accurate $V_{th}$ prediction of DG devices with the gate length up to 20-nm.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.10
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• pp.15-22
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• 2008

The bulk-planer MOSFET has a scaling limitation due to the short channel effect (SCE). The Double-Gate MOSFET (DG-MOSFET) is a next generation device for nanoscale with excellent control of SCE. The quantum effect in lateral direction is important for subthreshold characteristics when the effective channel length of DG-MOSFET is less than 10nm, Also, ballistic transport is setting important. This study shows modeling and design issues of nanoscale DG-MOSFET considering the 2D quantum effect and ballistic transport. We have optimized device characteristics of DG-MOSFET using a proper value of $t_{si}$ underlap and lateral doping gradient.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.168-172
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• 2011

Alumina powder was added in a general porcelain (Backja) with clay, feldspar and quartz contents to promote the mullite ($3Al_2O_3{\cdot}2SiO_2$) generation in the porcelain. Low melting materials ($B_2O_3(450^{\circ}C)$, $MnO_3(940^{\circ}C)$, CuO($1080^{\circ}C$)) were doped at ~3 wt% to modify the sinterability of porcelain with a high alumina contents and promote the mullite generation. Green body was made by slip casting method with blended slurry and then, they were fired at $1280^{\circ}C$ for 1hr by a $2^{\circ}C/min$. Densifications of samples with high alumina contents (20~30 wt%) were impeded. As the doping contents of low melting materilas increased, the sinterability of samples was improved. The shrinkage rate and bulk density of samples were improved by doping with low melting materials. Mullite phase increased with increasing the low melting contents in the phase analyses. This means lots of alumina and quartz were transformed into mullite phase by low melting contents doping. In the results, high bending strength of samples with high alumina contents was accomplished by improving the densification and mullite generation in the porcelain.

• Journal of the Korean Institute of Telematics and Electronics
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• v.20 no.1
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• pp.22-26
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• 1983

P+N and P+NN+ solar cells with the area of 3.36 $\textrm{cm}^2$ were fabricated by thermal diffusion. Under the light intensity of 100 mW/$\textrm{cm}^2$, total area(active area) conversion efficiency was 13.4%(14.7%) for P+N cell fabricated by 15 min boron predeposition at 94$0^{\circ}C$ and 20 min annealing at 80$0^{\circ}C$, and 14.3%(15.6%) for P+NN+ cell processed by 15 min boron predeposition at 94$0^{\circ}C$ and 50 min annealing at 80$0^{\circ}C$ after 20 min back phosphorus diffusion at 1,05$0^{\circ}C$. The minority carrier lifetime in bulk of P+NN+ cells was increased about 2~3 times comparing with P+N cells because of guttering and BSF effect due to back phosphorus doping. The methods used for efficiency improvement were AR coating, Ag electroplating, back doping and fine grid pattern as well as the control of front doping profile.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.508-517
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• 2014

We design and analyze the n-channel junctionless fin-shaped field-effect transistor (JL FinFET) with 10-nm gate length and compare its performances with those of the conventional bulk-type fin-shaped FET (conventional bulk FinFET). A three-dimensional (3-D) device simulations were performed to optimize the device design parameters including the width ($W_{fin}$) and height ($H_{fin}$) of the fin as well as the channel doping concentration ($N_{ch}$). Based on the design optimization, the two devices were compared in terms of direct-current (DC) and radio-frequency (RF) characteristics. The results reveal that the JL FinFET has better subthreshold swing, and more effectively suppresses short-channel effects (SCEs) than the conventional bulk FinFET.

• Progress in Superconductivity
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• v.11 no.1
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• pp.67-71
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• 2009

The effect of Cu substitution on the structural and superconducting properties of the $(Ru_{1-x}Cu_x)Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$ system with x = 0, 0.25 and 0.5 prepared under ambient pressure have been investigated. The X-ray diffraction patterns indicated that the Ru ions are replaced by the Cu ions. It is found that the Cu substitution for Ru significantly reduces the ferromagnetic component of field-cooled magnetic susceptibility, but results in a small change in diamagnetic onset transition temperature of zero-field-cooled magnetic susceptibility. In contrast to the Ru $Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$, bulk Meissner effect is observed in the field-cooled magnetization measurements of the Cu doped samples. The experimental results are discussed in connection with the spontaneous vortex phase interpretation.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.737-739
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• 1992

The microstructure and humidity sensitive characteristics of $V_2O_5$ doped $CaTiO_3$ were studied. Sensing elements were prepared in bulk form. This element exhibits a porous structure. The grain grows and electrical conductivity increases as doping amount of $V_2O_5$ increases. The change of impedance and capacitance under different r.h is remarkable, and the conduction carriers of this element were ions.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.248-248
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• 2010

We have demonstrated new functionalities of Ag-doped chalcogenide glasses based on their capabilities as solid electrolytes. The influence of silver on the properties of the newly formed materials is regarded in terms of diffusion kinetics, and Ag saturation is related to the composition of the hosting material. Silver saturated in chalcogenide glass has been used in the formation of solid electrolyte, which is the active medium in the programmable metallization cell (PMC) device. In this paper, we investigated the optical properties of Ag-doped chalcogenide thin film by He-Ne laser beam exposure, which is concerned with the Ag-doping effect of PMCs before or after annealing. Chalcogenide bulk glass was fabricated by a conventional melt quenching technique. Amorphous chalcogenide and Ag thin films were prepared by e-beam evaporation at a deposition rate of about $4\;{\AA}/sec$. As a result of resistance change with laser beam exposure, the resistance abruptly dropped from the initial value of $1.4\;M{\Omega}$ to the saturated value of $400\;{\Omega}$.