• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.3
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• pp.210-224
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• 2006

A new analytical model for the static I-V characteristics of GaAs MESFET’s under optically controlled conditions in both linear and saturation region is presented in this paper. The novelty of the model lies in characterizing both photovoltaic (external, internal) and photoconductive effects. Deep level traps in the semi insulating GaAs substrate are also included in this model. Finally, effect of backgate voltage on I-V characteristics is explained analytically for the first time in literature. Small signal parameters of GaAs MESFET are derived under both dark and illuminated conditions. Some of the results are compared with reported experimental results to show the validity of the proposed model. Since accurate dc modeling is the key to accurate ac modeling, this model is very useful in the designing of photonic MMIC’s and OEIC’s using GaAs MESFET.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.11
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• pp.894-901
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• 1991

Contact-type linear image sensors have been fabricated by means of RF glow discharge decomposition method of silane and hydrogen mixtures. The dependences of the electrical and optical properties of these sensor on thickness, RF power, substrate temperature and ambient gas pressure have been investigated. the ITO/i-a-Si:H/Al structure film shows photosensitivity of 0.85 and photocurrent to dark current ratio ($I_{ph}/I_{d}$) of 150 at 5V bias voltage under 200${\mu}W/cm^[2}$ red light intensity. Under 200${\mu}W/cm^[2}$ green light intensity, the ratio is 100. In order to investigate photocarrier transport mechanism and to obtain ${\mu}{\gamma}$ product we have measured the I-V characteristics of these sensors favricated with several different deposition parameters under various light sources. The linear inage sensor for document reading has been operated under reverse bias condition with green light source, resulting in ${\mu}{\gamma}$ product of about 1.5$[\times}10^{-9}cm^{2}$/V.

• Journal of radiological science and technology
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• v.33 no.3
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• pp.289-294
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• 2010

The purpose of this study is an evaluation of the performance of a detector under radiographic irradiation condition by fabricating the polycrystalline $HgI_2$ film detector. The polycrystalline $HgI_2$ film detectors with thickness of 210 and $320\;{\mu}m$ were fabricated by screen print technology. Measurements of X-ray sensitivity and dark current were performed for two detectors. And measurements of the linearity of X-ray response and reproducibility were performed for the detector of thickness $320\;{\mu}m$. For applied electric field strengths from 0.05 to $2\;V/{\mu}m$ to the detector of thickness $320\;{\mu}m$, the X-ray sensitivities were measured from 233 to $1,408{\times}106\;electrons/mR{\cdot}mm^2$. And the dark currents were measured from 3.2 to $118\;pA/mm^2$. Compared with values reported by Zhong Su et al., the X-ray sensitivities exhibit about two times larger than the X-ray sensitivities measured by Zhong Su et al. And the dark currents exhibit about nine times larger than the dark currents measured by Zhong Su et al. The linearity of X-ray response acquired 0.988 as a coefficient of correlation (r). Reproducibility acquired 0.002 as a coefficient of variation. This study provides the performance data of fabricated polycrystalline $HgI_2$ film detector available for an active matrix flat panel imager under radiographic irradiation condition.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.196-208
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• 2007

An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1547-1549
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• 1996

The electrical and optical switching characteristics of gold-doped silicon p-i-n diodes have been investigated. The device shows a dark switching voltage of about 500 V. The switching voltage decreases rapidly when the illumination level is increased. The differential sensitivity of optical gating over linear region is $d(V_{Th}/V_{Tho})/dP_{Ph}$=0.25/uW. The turn-on delay time and the turn-on rise time decrease with increasing optical pulse power. The turn-off delay and the fall time are negligible.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.98-103
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• 2009

In this paper, we test the electrical resistance of flat wire in the PV module. normally solar cell has two kind of flat wire(inter connection ribbon and bus bar ribbon). we found the phenomenon that has a unbalance with resistance when we make a wiling between of string. So, we measurement the resistance of flat wire each other. and analysis of missmatch with resistance between flat wires on PV module. next to survey of IR picture on missmatch flat wire samples for analyze of missmatch with current in the wire. and we perform IR test with solar cell that has a connection with flat wire for test the effect of missmatch resistance on solar cell. Finally we perform the Dark I-V test for survey of effect by the unbalance of resistance. By the result of Dark I-V test, the series resistance of existing connection sample is large more then innovated connection sample.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.46.1-46.1
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• 2013

High velocity clouds (HVCs) are H I clouds that move with large speed (${\mid}V_{LSR}{\mid}$ >100 km/s) in the halo of the Milky Way. It is now evident that at least some populations of HVCs originated from extragalactic sources, either primordial gas left over from the galaxy formation or gaseous material stripped off from other galaxies closely passing by the Milky Way. HVCs with extragalactic origin play an important role in the star formation of the Milky Way when they eventually collide with the disk of the Milky Way. Although it is still observationally controversial whether HVCs are surrounded by dark matter or not, it is theoretically interesting to investigate the effect of dark matter on the collision of HVCs with the disk of the Milky Way. We model this scenario by using hydrodynamic simulations and search for proper parameters that explain the currently available observations such as the Smith Cloud that is thought to have collided with the Galactic disk already.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.6
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• pp.48-56
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• 1989

Contact-type linear image sensors for facsimile have been fabricated by means of rf glow discharge decomposition method of silane. The dependence of their electrical and optical properties on rf power, $SiH_4$ flow rate, ambient gas pressure, $H_2SiH_4$ ratio and substrate temperature are described. The a-Si:H monolayer demonstriated photosensitivity of 0.85 and $I_{ph}/I_d$ ratio of 100 unger 100 lux illumination. However, this monolayer has relatively high dark current due to carrier injection from both electrodes, resulting in low $I_{ph}/I_{dd}$ ratio. To suppress the dark current we have fabricated $SiO_2/i-a-Si:H/p-a-Si:H:B$ multilayer film with blocking structure. The photocurrent of this multilayer sensor with 6 V bias became saturated ar about 20nA under 10 lux illumination, while the dark current was less than 0.2 nA. Moreover, the spectral sensitivity of the multilayer film was enhanced for short wavelength visible region, compared with that of the a-Si:H monolayer. These results show that the fabricated photocon-ductive film can be used as the linear image sensor of the facsimile.

• Journal of the Korean Vacuum Society
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• v.19 no.3
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• pp.217-223
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• 2010

We grew multi-stacked InAs/$In_{0.1}Ga_{0.9}As$ DWELL (dot-in-a-well) structure by metal organic chemical vapor deposition and investigated optical properties by photoluminescence and I-V characteristics by dark current measurement. When stacking InAs quantum dots (QDs) with same growth parameter, the size and density of QDs were changed, resulting in the bimodal emission peak. By decreasing the flow rate of TMIn, we achieved the uniform multi-stacked QD structure which had the single emission peak and high PL intensity. As the growth temperature of n-type GaAs top contact layer (TCL) is above $600^{\circ}C$, the PL intensity severely decreased and dark current level increased. At bias of 0.5 V, the activation energy for temperature dependence of dark current decreased from 106 meV to 48 meV with increasing the growth temperature of n-type GaAs TCL from 580 to $650^{\circ}C$. This suggest that the thermal escape of bounded electrons and non-radiative transition become dominant due to the thermal inter-diffusion at the interface between InAs QDs and $In_{0.1}Ga_{0.9}As$ well layer.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.72-75
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• 2012

In our experiments, strain-free nanowires(NWs) were dispersed on to the substrate, followed by e-beam lithography(EBL) to fabricate single nanowire ultraviolet(UV) sensor devices. Focused-ion beam(FIB), micro-Raman spectroscopy and photoluminescence were employed to characterize the structural and optical properties of AlGaN/GaN NWs. Also, I-V characteristics were obtained under both dark condition and UV lamp to demonstrate AlGaN/GaN NW-based UV sensors. The conductance of a single AlGaN/GaN UV sensor was 9.0 ${\mu}S$(under dark condition) and 9.5 ${\mu}S$ (under UV lamp), respectively. The currents were enhanced by excess carriers under UV lamp. Fast saturation and decay time were demonstrated by the cycled processes between UV lamp and dark condition. Therefore, we believe that AlGaN/GaN NWs have a great potential for UV sensor applications.