• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.191.2-191.2
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• 2013

The negative photoconductivity was frequently observed in some semiconductors. It was known that the origin of the negative photoresponse from ZnO is molecular chemisorption or the charging effect of nanoparticles in bulk matrix. However, the origin of the negative photoresponse of thin film was not still clear. One of possible explanation is due to the deep level trap scheme, which describes the origin of the negative photoresponse via defect state under illumination of light. However, the defect states below Fermi level have high capture rate by Coulomb effect, so that these states are usually filled by electrons if the defect states have donor-like character. Therefore the condition which the defect states located in below Fermi level should be partially filled by electrons make more difficult to understand of mechanism of the negative photoresponse. In this study, n-ZnO/p-Si heterojunction diodes were fabricated by UHV RF magnetron sputter. Then, some diodes show the negative photoresponse under ultra-violet light illumination. The defect state of the ZnO was analyzed by photoluminescence and deep level transient spectroscopy. To interpret the negative photoconductivity, band diagram was simulated by using SCAPS program.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.6
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• pp.576-580
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• 2013

We investigate the enhanced effects of asymmetry ratio variations of the source and drain area in silicon (Si) field-effect transistor (FET). Photoresponse according to the variation of asymmetry difference between the width of source and drain are obtained by using the plasmonic terahertz (THz) wave detector simulation based on technology computer-aided design (TCAD) with the quasi-plasma 2DEG model. The simulation results demonstrate the potential of Si FETs with asymmetric source and drain structures as the promising plasmonic THz detectors.

• Elastomers and Composites
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• v.56 no.4
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• pp.250-253
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• 2021

Polypyrrole is an organic thermoelectric material which has been receiving extensive attention in recent years. Polypyrrole is applicable in various fields because its electrical properties are controllable by its doping concentration. In this study, the effects of the polypyrrole doping state on its photoresponse were investigated. The degree of doping was controlled by ammonia solution treatment. Then, the chemical structure as a function of the doping states was observed by Raman analysis. Moreover, the photocurrent and photovoltage characteristics for various doping states were measured by an asymmetrically irradiated light source. As the degree of doping increased, the electrical conductivity increased, which affected the photocurrent. Meanwhile, the photovoltage was related to the temperature gradient caused by light irradiation.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.520-526
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• 1994

A rectifying heterojunction consisting of polyparaphenylene(PPP) and polypyrrole(PPY) films was prepared by the electrochemical method. The photoresponse in the heterojunction of PPY and PPP is similar to the absorption spectrum of undoped PPP. This fact suggests that photoresponse depends strongly upon polyparaphenylene of semiconductor. The fill-factor was calculated from the photo current-voltage curve to be 0.19, which is relatively small compared to polyacetylene-polythiophene heterojunctions.

• Proceedings of the KIEE Conference
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• 2005.11a
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• pp.60-61
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• 2005

Electrodes were fabricated on a single ZnO nanowire by photolithography process, metal evaporation, and lift-off. The slow photoresponses of the ZnO nanowire under the continuous illumination of 325nm-wavelength light (corresponding to above-bandgap excitation) indicate that the traps related to oxygen vacancy disturb the flow of electron in ZnO nanowire. The photoresponse and PL spectra were measured, and observed that the excitonic band in the PL spectrum was absent in the photoresponse.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.207-207
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• 2008

ZnO is one of the widely utilized n-type semiconducting oxide materials in the field of optoelectronic devices. For its application to the fabrication of promising ultraviolet (UV) photodetectors, ZnO with various structures has been extensively studied. However, study on the photodetectors using zero-dimensional (0-D) ZnO nanoparticle is scarce while the 0-D nanoparticle structure has many advantages compared to the other dimensional structures for absorption of light. In this study, the photocurrent characteristics of ZnO nanoparticles were investigated through a simply pasting of the nanoparticles across the pre-patterned electrodes. Then the photoluminescence (PL) characteristic, photocurrent response spectrum, photo- and dark-current and photoresponse spectrum were investigated with a He-Cd laser and an Xe lamp. An dominant PL peak of the ZnO nanoparticles was located at the wavelength of 380 nm under the illumination of 325-nm wavelength light. The ratio of photocurrent to dark current (on/off ratio) is as high as 106 which is considerable value for promising photodetectors. On the other hand, the time constants in photoresponse were relatively slow. The reasons of the high on/off ratio and relatively slow photoresponse characteristic will be discussed.

• Transactions on Electrical and Electronic Materials
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• v.5 no.3
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• pp.93-97
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• 2004

Structural and optoelectronic properties of as-synthesized SnO$_2$ nanowires were examined in this study. The SnO$_2$ nanowires were first synthesized by thermal evaporation of ball-milled SnO$_2$ powders in argon atmosphere without the presence of any catalysts, arid their structural properties are then investigated by X-ray diffraction, Raman scattering, scanning electron microscopy, and transmission electron microscopy. This investigation revealed that the synthesized SnO$_2$ nanowires are single-crystalline and that their growth direction is parallel to the [100] direction. In addition, photoresponse of a single SnO$_2$ nanowire was performed with light with above-gap energy, and different characteristics of photoresponses were obtained for the nanowire at ambient atmosphere and in vacuum. The photoresponse mechanism is briefly discussed in this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.25-28
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• 2004

Photocurrent spectrum, photoresponse, and I-V measurements were made for close-packed HgTe nanoparticles without organic capping materials to investigate their photocurrent characteristics in the infrared range. In absorption and photoluminescence (PL) spectra taken for the close-packed nanoparticles film, the wavelengths of exciton peaks was red-shifted, compared with organic capped HgTe nanoparticles dispersed in solution. This red-shift is caused by the lessening of the exciton binding energy. The I-V curves and photoresponse for the close-packed nanoparticles film reveal their dark current and fast photoresponse with no current decay, respectively. The observation suggests that the HgTe nanoparticles are a very prospect material applicable for photodetectors in the whole IR range.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.33-34
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• 2005

Electrodes were fabricated on a single ZnO nanowire by photolithography process, metal evaporation, and lift-off. The slow photoresponses of the ZnO nanowire under the continuous illumination of 325nm-wavelength light (corresponding to above-bandgap excitation) indicate that the traps related to oxygen vacancy disturb the flow of electron in ZnO nanowire. The photoresponse and PL spectra were measured, and observed that the excitonic band in the PL spectrum was absent in the photoresponse.

• Journal of Sensor Science and Technology
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• v.28 no.2
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• pp.117-120
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• 2019

Graphene is recognized as a promising material for silicon photonics, since it has a wide optical-window that entirely covers the optical communication wavelength region ($1.3{\sim}1.6-{\mu}m$) and extremely high-carrier mobility that makes it possible to fabricate the high-speed photodetectors. However, the maximum absorbance of monolayer graphene is only 2.3%, which limits the photoresponse characteristics of graphene photodetectors. As a result, a low photoresponsivity of graphene photodetector is a critical issue limiting the use of graphene photodetectors in the optical communications field. In this paper, we investigated effects of optically-modulated metal-graphene contact on the photoresponsivity of graphene photodetectors. The optical modulation of the contact resistance mainly determined the photoresponse characteristics of graphene photodetectors. The Ni-contact graphene photodetector which has a characteristic of the significant optical modulation of metal-graphene contact showed a higher photoresponsivity than the Pd-contact device. This work will provide a way to improve the photoresponse characteristics of graphene-based photodetector and contribute to the development of high-speed/high-responsivity graphene photodetector.