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Optically Controlled Silicon MESFET Modeling Considering Diffusion Process
S. N. Chattopadhyay,N. Motoyama,A. Rudra,A. Sharma,S. Sriram,C. B. Overton,P. Pandey 대한전자공학회 2007 Journal of semiconductor technology and science Vol.7 No.3
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 VT 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 Vgs is significantly increased with optical illumination for photon flux densities of Φ = 10<SUP>15</SUP> and 10<SUP>17</SUP> /㎠s compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage VDS is evaluated to find the I-V characteristics for various pinch-off voltages VP for optimization of impurity flux density QDiff 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 Cgs and gate-drain capacitance Cgd for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time τ of the OPFET device is computed for dark and illumination conditions. The switching time τ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density QDiff. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.
Optically Controlled Silicon MESFET Modeling Considering Diffusion Process
Chattopadhyay, S.N.,Motoyama, N.,Rudra, A.,Sharma, A.,Sriram, S.,Overton, C.B.,Pandey, P. The Institute of Electronics and Information Engin 2007 Journal of semiconductor technology and science Vol.7 No.3
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.
EFFECTS OF OZONATION AND CHLORINATION ON VIABILITY AND INFECTIVITY OF CRYPTOSPORIDIUM PARVUM OOCYSTS
Hirata, T.,Chikuma, D.,Shimura, A.,Hashimoto, A.,Motoyama, N.,Takahashi, K.,Moniwa,T.,Kaneko, M.,Saito, S.,Maede, S. 嶺南大學校 環境問題硏究所 1999 環境硏究 Vol.19 No.1
ABSTRACT Experimental studies on ozonation and chlorination were conducted to determine capacity for inactivating Cryptosporidium parvum oocysts in batch modes at pH 7, 20℃. In both experiments, the log reduction of animal infectivity was linear and clearly decreased as disinfectant CT product increased. However, the curve of reduction in viability determined by both in vitro excystation assay and DAPI/PI permeability assay exhibited a shoulder. The CT products of ozone per 1 log reduction in infectivity were 3 mg·min/L for 0.5 mg/L and 1.5mg·min/L for 0.3 mg/L, while viability determined by in vitro excystation was reduced by only 0.2 logs for the CT product of 3 mg·min/L. In the chlorination experiment, the reduction of animal infectiviry was up to 3 logs for the CT product of 2,700 mg·min/L, while reduction of viability was smaller at 0.16 logs in in vitro excystation and 0.04 logs in DAPI/PI permeability (in PI exclusion)for the same CT product. The CT product of free chlorine per 1 log reduction in infectivity was estimated to be in the range of 800 to 900 mg·min/L Experimental studies on ozonation and chlorination were conducted to determine capacity for inactivating Cryptosporidium parvum oocysts in batch modes at pH 7, 20℃. In both experiments, the log reduction of animal infectivity was linear and clearly decreased as disinfectant CT product increased. However, the curve of reduction in viability determined by both in vitro excystation assay and DAPI/PI permeability assay exhibited a shoulder. The CT products of ozone per 1 log reduction in infectivity were 3 mg·min/L for 0.5 mg/L and 1.5 mg·min/L for 0.3 mg/L, while viability determined by in vitro excystation was reduced by only 0.2 logs far the CT product of 3 mg·min/L. In the chlorination experiment, the reduction of animal infectivity was up to 3 logs for the CT product of 2,700 mg·min/L, while reduction of viability was smaller at 0.16 logs in in vitro excystation and 0.04 logs in DAPI/PI permeability (in PI exclusion) far the same CT product. The CT product of free chlorine per 1 log reduction in infectivity was estimated to be in the range of 800 to 900 mg·min/L.