• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.355-355
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• 2010

We studied the dependence of the performance of schottky barrier metal-oxide-field effect transistors(SB MOSFETs) on the work function of source/drain metals. A strong impact of the various work functions and the light wavelengths on the transistor characteristics is found and explained using experimental data. We used an insulator of a high thickness (100nm) and back gate issues in SOI substrate, subthreshold swing was measured to 300~400[mV/dec] comparing with a ideal subthreshold swing of 60[mV/dec]. Excellent characteristics of Al/Si was demonstrated higher on/off current ratios of ${\sim}10^7$ than others. In addition, extensive photoresponse analysis has been performed using halogen and deuterium light sources(200<$\lambda$<2000nm).

• Current Optics and Photonics
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• v.6 no.4
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• pp.367-374
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• 2022

A photodetector based on a reduced graphene oxide (RGO)/n-Si heterojunction with high responsivity, detectivity and fast response speed is presented. Here, we put forward a simple vacuum filtration method to prepare RGO film and transfer it onto an n-Si substrate to form an RGO/n-Si heterojunction. The experimental results show that the heterojunction has good rectification characteristics, and the response and recovery time are less than 0.31 s and 0.25 s, respectively. Under 470 nm light conditions at -2 V applied voltage, the responsivity and detectivity of the device are 65 mA/W and 4.02 × 10¹⁰ cmHz^1/2W^-1, respectively. The simple preparation process and good performance of the RGO/n-Si heterojunction make it a promising material for photoelectric detection, especially in the near-ultraviolet band.

• Journal of IKEEE
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• v.10 no.2 s.19
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• pp.161-167
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• 2006

The effect of aging on the optoelectronic properties of a single ZnO nanowire is investigated in this study. The photoluminescence (PL), photocurrent spectrum, current-voltage characteristics, and photoresponse were measured for the as-grown ZnO nanowire and for the same nanowire exposed to air for three months. For the aged nanowire, the broad PL band is weaker, the intensity of the photocurrent is strengthened, and the photoresponse is slower, compared with the as-grown nanowire. It Is suggested in this paper that the observed aging effect on the PL is due to the reduction in the number of oxygen vacancies within the nanowire and that the aging effect on the photocurrent and photoresponse originates from the formation of oxygen vacancies near the surface.

• Korean Journal of Materials Research
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• v.29 no.9
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• pp.542-546
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• 2019

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : $n^+-i(QD)-n^+$ QDIP with undoped quantum dot(QD) active region and $n^+-n^-(QD)-n^+$ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the $n^+-n^-(QD)-n^+$ structure, Si dopant is directly doped in InAs QD at $2{\times}10^{17}/cm^3$. Undoped and doped QDIPs show a photoresponse peak at about $8.3{\mu}m$, ranging from $6{\sim}10{\mu}m$ at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.110-111
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• 2014

RGB laser 를 이용하여 rf-magnetron sputtering 법으로 합성한 a-IGZO 박막의 photoresponse 를 관찰하였다. Air 분위기에서 red 파장을 조사 할 경우 비교적 slow recovery 특성을 보였으며, green 과 blue 파장을 조사 할 경우 red 보다 fast recovery 특성을 나타내었다. 그러나 진공에서 측정할 경우, red 파장에서는 recovery 가 빨라졌으며, green 과 blue 파장의 경우 recovery 가 매우 느려짐을 확인하였다. 이는 passivation 을 하지 않은 소자의 oxygen gas 의 흡/탈착 때문으로 예상할 수 있었으며, red 파장이 gas 탈착에 기여하는 정도가 매우 작고, green 과 blue 파장이 gas 탈착에 기여하는 정도가 매우 크기 때문인 것으로 생각할 수 있었다. 온도를 증가시킬 경우, 모든 경우에서 recovery 가 빠르게 나타났는데 이는 흡/탈착에 필요한 barrier 및 $V_o{^{2+}}$에서 Vo 로 돌아오기 위한 barrier 를 쉽게 넘어갈 수 있기 때문으로 이해 할 수 있었다. 이러한 결과를 stretched exponential equation 을 이용하여 해석하였으며 수치화 하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.70-73
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• 2004

Two different $SnO_2$ nanomaterials(nanowires and nanobelts) were synthesized from the thermal evaporation of ball-milled $SnO_2$ powders at $1350^{\circ}C$ without the presence of any catalysts, and their structural properties are then investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This investigation reveals that the $SnO_2$ nanowires are single-crystalline and their growth direction is parallel to the [100] direction, and that the $SnO_2$ nanobelts are single crystalline and their shape is zigzag. In addition, photoresponse of a single $SnO_2$ nanowire was performed with light above-gap energy, and different characteristics of photoresponse were obtained for the nanowire at ambient atmosphere and in vacuum.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.127-127
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• 2010

Owing to many advantages on indirect intersubband absorption from the hole miniband to the electron miniband based on the type-II band alignment in InAs/GaSb strained-layer superlattice (SLS), InAs/GaSb SLS infrared photodetector (SLIP) has emerged as a promising system to realize high-detectivity quantum photodetector operating up to room temperature in the spectral range of mid-infrared (MIR) to far-infrared (FIR). In particular, n-barrier-n (n-B-n) structure designed for blocking the majority-carrier dark current makes it possible for MIR/FIR dual-band SLIP whose photoresponse (PR) band can be exclusively selected by the bias polarity. In this study, we present the MIR and FIR photoresponse (PR) mechanism identified by dual-band PR spectra and photoluminescence (PL) profiles taken from InAs/GaSb SLIP. In the MIR/FIR PR spectra measured by changing bias polarity, each spectrum individually shows a series of distinctive peaks related to the transitions from the hole subbands to the conduction one. The PR mechanism at each polarity is discussed in terms of diffusion current, and a superposition of MIR-PR in the FIR-PR spectrum is explained by tunnelling of electrons activated in MIR-SLS. The effective FIR-PR spectrum decomposed into three curves for HH1, LH1, and HH2 has revealed the edge energies of 120, 170, and 220 meV, respectively, and the temperature variation of the MIR-PR edge energies shows that the temperature behavior of the SLS systems can be approximately expressed by the Varshni empirical equation.

• Journal of Sensor Science and Technology
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• v.30 no.5
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• pp.279-285
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• 2021

Recently, cesium tellurium iodine (Cs₂TeI₆) has emerged as an inorganic halide perovskite material with potential application in optoelectronic devices due to its high absorption coefficient, suitable bandgap and because it consists of nontoxic and earth-abundant elements. However, studies on its fabrication process as well as photoresponse characteristics are limited. In this study, a simple and effective method is introduced for the synthesis of Cs₂TeI₆ thin films by a two-step dry process. A Cs₂TeI₆-based lateral photosensor was fabricated, and its photoresponse characteristics were explored under laser illuminations of four different wavelengths in the visible range: 405, 450, 520, and 655 nm. The initial photosensing results suggest potential application and can lead to more promising studies of Cs₂TeI₆ film in optoelectronics.

• Journal of IKEEE
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• v.13 no.1
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• pp.57-64
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• 2009

The optoelectrical characteristics of the ZnO nanoparticles (NPs) annealed in vacuum or oxygen condition from $200^{\circ}C$ to $600^{\circ}C$ were examined. Increased on-off ratio (or, the ratio of photocurrent to dark current) was observed when they were annealed at $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$ with the values enhanced about 4 orders compared to the as-prepared ZnO NPs in both annealing conditions, while the maximum efficiency was shown at the annealing temperature of $600^{\circ}C$ for the ZnO NPs annealed in vacuum with the value of 29.8 mA/W and at the temperature of $500^{\circ}C$ for those annealed in oxygen condition with the value of 40.3 mA/W. Photoresponse behavior of the ZnO NPs annealed in oxygen showed the sharp increase right after the ir exposure to the light followed by the slow decay and saturation during steady illumination, differing from the ZnO NPs annealed in vacuum which only exhibited the gradual increase. This difference occurred due to the curing effect of the oxygen vacancies. SEM images indicated no change in their morphologies with annealing, indicating the change in their internal structures by annealing, and most remarkably at $600^{\circ}C$. As for their photoluminescence(PL) spectra, the decrease of the deep-level(DL) emission was observed when they were annealed in oxygen at $400^{\circ}C$, and not at $200^{\circ}C$ and $600^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.806-811
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• 2017

An all-transparent ultraviolet (UV) photodetector was fabricated by structuring $p-NiO/n-SnO_2/ITO$ on a glass substrate. $SnO_2$ is an important semiconductor material because of its large bandgap, high electron mobility, high transmittance (as high as 80% in the visible range), and high stability under UV light. For these reasons, $SnO_2$ is suitable for a range of applications that involve UV light. In order to form a highly transparent p-n junction for UV detection, $SnO_2$ was deposited onto a device containing NiO as a high-transparent metal conductive oxide for UV detection. We demonstrated that all-transparent UV photodetectors based on $SnO_2$ could provide a definitive photocurrent density of $4nA\;cm^{-2}$ at 0 V under UV light (365 nm) and a low saturation current density of $2.02nA{\times}cm^{-2}$. The device under UV light displayed fast photoresponse with times of 31.69 ms (rise-time) and 35.12 ms (fall-time) and a remarkable photoresponse ratio of 69.37. We analyzed the optical and electrical properties of the $NiO/SnO_2$ device. We demonstrated that the excellent properties of $SnO_2$ are valuable in transparent photoelectric device applications, which can suggest various routes for improving the performance of such devices.