• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.11
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• pp.1373-1379
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• 1988

This paper describes a two-dimensional analysis of the potential distribution and electron concentration of the MODFET at channel using FDM. More exact analysis can be obtained by two-dimensional analysis which considers parasitic effects ignored in one-dimensional analysis. Using Poisson and Shrodinger equations, the potential distribution and the wave function are calculated within a constant error bound. As a result, the relations between the thickness of spacer, doping concentration of (n) AlGaAs layer, and the sheet density of the 2DEG (2 Dimensional Electron Gas) of MODFET at channel are suggested quantitively. The sheet density of the 2DEG is increased as the thickness of the spacer is decreased of the doping concentration of the (n)AlGaAs layer is lowered.

• Journal of the Korean Magnetics Society
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• v.3 no.4
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• pp.305-309
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• 1993

Thermal stability of Co/Cu artificial superlattice (AS) prepared by RF-magnetron sputtering and the effect of low temperature annealing on the magnetoresistance of the AS have been investigated in this work. Dependence of annealing behavior on the Cu spacer thickness, Fe underlayer thickness, and kind of the underlayer was examined and the relationship between the interfacial reaction and magnetoresistance was studied. It turned out that when Co/Cu AS was annealed at low temperature ($<450^{\circ}C$), the magnetoresistance could increase in the case of AS with thick spacer Cu ($20~25\AA$) layer, whereas it decreased in the case of AS with thin spacer Cu ($7\AA$) layer, which of the former is in contrast with previous reports and the latter in consistent with them. The increase of magnetoresistance is due to increase of interfacial atomic sharpness, which is supported by low angle X-ray diffraction analysis. The thermal stability of Co/Cu AS was better in the case of thick Fe underlayered AS. Interfacial reaction (separation of intermixed Co and Cu) could be observed at lower temperature for (200)-textured samples than for (111)-textured samples, which can be interpreted in terms of interdiffusion kinetics depending on the crystallographic orientation.

• Journal of the Korean Vacuum Society
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• v.7 no.3
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• pp.208-213
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• 1998

Silicidation of the Co/Ti/Si bilayer system in which Ti is used as epitaxy promoter for $CoSi_2$has recently received much attention. The Co/Ti bilayer on the spacer oxide of gate electrode must be thermally stable at high temperatures for a salicide transistor to be fabricated successfully. In the $SiO_2$substrate was rapid-thermal annealed. The Sheet resistances of the Co/Ti bilayer increased substantially after annealing at $600^{\circ}C$, which is due to the agglomeration of the Co layer to reduce the interface energy between the Co layer and the $SiO_2$substrate. In the bilayer system insulating Ti oxide stoichiometric Ti oxide and silicide were not found after annealing.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.465-468
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• 1987

This paper describes a model to calculate the equilibrium electron density of MODFET at the interface that takes into account the simultaneous shallow and deep level in the Al-GaAs layer. In the present study we have made an investigation of the interface electron density with different values of the AlGaAs doping density and spacer layer thickness, considering simultaneously two doner levels. In this case, the ratio of the shallow to the deep donor concentraction is considered. From the comparison with early experimental results we could find the deep level and that the deep donor concentration is about 50% with the Al mole fraction X ${\sim}0.3$, activation energy Edx=65meV, temperature $77^{\circ}K$ and spacer thickness range $50A{\sim}100A$. Also we have investigated the effect of the temperature. As temperature increase, at critical mole fraction X the nature of the donor concentration changes from $\Gamma$ to L and X.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.7
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• pp.1036-1043
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• 1993

GaAs/AIGaAs resonant tunneling structures have been grown by atmospheric pressure MOCVD. Resonant tunneling diodes fabricated with the structure grown at 650t showed a high peak-to-valley (P/V) current ratio of 2.35 at room temperature. P/V current ratio increased to 15.3 at 77K. Numerically calculated peak current agrees well with the experimental result. Resonant tunneling diodes with AIGaAs as a barrier and InGaAs as a quantum well and a spacer layer yielded a high P/V current ratio of 4.0 and a peak current density of 8.6KA/c# at room temperature because of increased carrier supply.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.186-186
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• 2006

We report a new architecture for high efficiency polymer solar cells introducing a new concept of 'optical spacer' with new material. By implementing a novel solution-based titanium oxide ($TiO_{x}$) layer between the active layer and the electron collecting Al electrode, we invented a way to increase ${\sim}50\;%$ in power conversion efficiency compared to conventional polymer solar cells. Now the new devices exhibit ${\sim}6\;%$ power conversion efficiency, which is the highest value reported to date for a polymer based photovoltaic cell. The $TiO_{x}$ layer increases the efficiency by modifying the spatial distribution of the light intensity inside the device, thereby creating more photogenerated charge carriers in the bulk heterojunction layer.

• Journal of Magnetics
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• v.3 no.3
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• pp.92-95
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• 1998

In this paper we report the low and high angle diffraction results, and the magnetic and magnetroesistive characteristics of the spin valve multilayer structure prepared by the sputter machine Emerald II in the Balzers Laboratory. The investigated system consists of a ferromagnetic free layer (7 nm NiFe) and a ferromagnetic pinned layer (7 nm NiFe), separated from each other by a nonmagnetic (2.1 nm Cu) spacer. The NiFe pinned layer is fixed by the exchange coupling with an antiferromagnetic layer (10 nm FeMn). For such system the magnetoresistance ratio ΔR/R=3.58%, the interlayer exchange coupling $H_c=6.4$ Oe and the field sensitivity 1.15%/Oe were otained.

• Korean Journal of Crystallography
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• v.12 no.3
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• pp.166-170
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• 2001

Dopants implanted in silicon substrate affect the reaction between cobalt and silicon substrate. Phosphorous, unlike boron and arsenic, suppressing the reaction between cobalt and silicon induces CoSi formation during a low temperature thermal treatment instead of CoSi₂formation. The CoSi layer should move to the silicon substrate to fill the vacant volume that is generated in the silicon substrate due to the silicon out-diffusion into the cobalt/CoSi interface. The movement of CoSi at gate sidewall spacer region is suppressed by a cohesion between gate oxide and CoSi layers, resulting in a void formation at the gate sidewall spacer edge.

• KSTLE International Journal
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• v.10 no.1_2
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• pp.27-32
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• 2009

In this study, fretting wear tests of nuclear fuel rods have been performed by using two kinds of spacer grid springs with a concave and a convex shape in room temperature dry and distilled water conditions. The objectives were to examine the variation of the wear mechanism with increasing fretting cycles and to evaluate the difference of the wear debris detachment behavior at each test environment. From the test results, the wear volume of each spring condition increased with increasing fretting cycles regardless of the test environments. However, the wear rate did not show a regular tendency and apparently changed with increasing fretting cycles. This is because the formation of the wear particle layer and/or the variation of the contact condition between the fuel rod and spring surfaces could affect a critical plastic deformation for detaching the wear debris. Based on the test results, the relationship between the wear behavior of each spring shape and test environment condition, and the variation of the surface characteristics are discussed in detail.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.86-92
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• 1999

A SiGe p-channel MESFET using $\delta$-doped layers is designed and the considerabel enhancement of the current driving capability of the device is observed from the result of simulation. The channel consists of double $\delta$-doped layers separated by a low-doped spacer which consists of Si and SiGe. A quantum well is formed in the valence band of the Si/SiGe heterojunction and much more holes are accumulated in the SiGe spacer than those in the Si spacer. The saturation current is enhanced by the contribution of the holes in the spacer. Among the design parameters that affect the performance of the device, the thickness of the SiGe layer and the Ge composition are studied. The thickness of 0~300$\AA$ and the Ge composition of 0~30% are investigated, and saturation current is observed to be increased by 45% compared with a double $\delta$-doped Si p-channel MESFET.