• Title/Summary/Keyword: amorphous-Selenium

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Time of Fight Resonace Investigation of Amorphous Selenium Films (비정질 셀레늄 필름의 공명 비행시간 조사)

  • Park, J.K.;Park, S.K.;Lee, D.G.;Choi, J.Y.;Ahn, S.H.;Eun, C.K.;Nam, S.H.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11b
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    • pp.501-504
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    • 2001
  • We used time-of-flight method to analyze transport properties of charge carrier which is produced by X-ray exposure. It is the research of charge transport and specific property of trap that is performed in direct digital x-ray image receptor. But the results shows us different measurement value of electron and charge drift mobility and it is difficult to precise analysis about charge transport properties and trap mechanism. We measured transit time and drift mobility of charge carriers using time-of-flight method to evaluate the correlation of a-Se thickness change and electric field. We made a testing glass with a-Se of 400 ${\mu}m$ thickness on coming glass using thermoevaporation method and built Au electrode with 300nm, $2{\varphi}$ on both sides of a-Se, As a result of this experiment, electron and hole transit time was each $229.17{\mu}s$ and $8.73{\mu}s$ at $10V/{\mu}m$ electric field and Drift mobility was each $0.00174 cm^{2}/V{\cdot}s$, $0.04584cm^{2}/V{\cdot}s$.

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Structure design of Csl-Se Detector using Monte Carlo Simulation (몬테카를로 시뮬레이션을 통한 Csl-Se 검출기의 구조 설계)

  • Park, Ji-Koon;Kang, Sang-Sik;Choi, Jang-Young;Lee, Hung-Won;Nam, Sang-Hee
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.11a
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    • pp.420-423
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    • 2002
  • In recent years, there has been keen interest in developing f1at panel detectors for all modalities of radiology, including gerneral radiology, fluoroscopy(angiography and cardiology), electronic portal imaging, and mammography. In this paper, we report the new hybrid x-ray detector consisted of CsI(Tl) photoemission layer and a-Se photoconductor layer to resolve conventional x-ray detector such as the direct detector using a-Se and the indirect detector using CsI(Tl)/a-Si. To design the structure of CsI(Tl)/a-Se detector, the penetrated energy spectrum and absorption fraction was estimated using MCNP 4C code. Experimental results showed that the absorption fraction of $500{\mu}m-Se$ film and $150{\mu}m-CsI\left(Tl \right)/a-Se\left( 30{\mu}m \right)$ film is 70% at 70 kVp. The absorption energy is 90% at $350{\mu}m-CsI(Tl)$.

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Transport Properties of Conversion Materials for Digital Radiography

  • Kim, Jae-Hyung;Park, Chang-Hee;Nam, Sang-Hee
    • Transactions on Electrical and Electronic Materials
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    • v.8 no.6
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    • pp.250-254
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    • 2007
  • Applying the moving photo-carrier grating(MPG) technique and time-of-flight(TOF) measurements, we studied the transport properties of stabilized amorphous selenium typical of the material used in direct conversion X-ray imaging devices. For MPG measurement, we obtained electron and hole mobility and the recombination lifetime of $\alpha-Se$ films with arsenic(As) additions. We found an apparent increase in hole drift mobility and recombination lifetime, especially when 0.3 % As was added into $\alpha-Se$ film, whereas electron mobility decreased with the addition of As due to the defect density. For TOF measurement, a laser beam with pulse duration of 5 ns and wavelength of 350 nm was illuminated on the surface of $\alpha-Se$ with a thickness of 400 ${\mu}m$. The measured hole and electron transit times were about 8.73 ${\mu}s$ and 229.17 ${\mu}s$, respectively.

Time of Flight Resonace Investigation of Amorphous Selenium Films (비정질 셀레늄 필름의 공명 비행시간 조사)

  • 박지군;박성광;이동길;최장용;안상호
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.501-504
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    • 2001
  • We used time-of-flight method to analyse transport properties of charge carrier which is produced by X-ray exposure. It is the research of charge transport and specific property of trap that is performed in direct digital x-ray image receptor. But the results shows us different measurement value of electron and charge drift mobility and it is difficult to precise analysis about charge transport properties and trap mechanism. We measured transit time and drift mobility of charge carriers using time-of-fight method to evaluate the correlation of a-Se thickness change and electric field. We made a testing glass with a-Se of 470 ${\mu}{\textrm}{m}$ thickness on corning glass using thermoevaporation method and built Au electrode with 300nm, 2$\phi$ on both sides of a-Se. As a result of this experiment, electron and hole transit time was each 229.17 $\mu$s and 8.737 $\mu$s at 10V/${\mu}{\textrm}{m}$ electric field and Drift mobility was each 0.00174 $\textrm{cm}^2$/V.s, 0.04584 $\textrm{cm}^2$/V.s.

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Multi-layer design of Hybrid method for digital X-ray imaging (디지털 X-ray imaging을 위한 Hybrid 방식의 다층구조 설계)

  • Cho, Sung-Ho;Park, Ji-Koon;Lee, Dong-Gil;Kim, Dae-Hwan;Kim, Jae-Hyung;Nam, Sang-Hee
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.05c
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    • pp.75-78
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    • 2003
  • In recent years, there has been keen interest in developing flat panel detectors for all modalities of radiology, including gerneral radiology, fluoroscopy, electronic portal imaging, and mammography. In this paper, we report the new hybrid x-ray detector consisted of ZnS(Ag) photoemission layer and a-Se photoconductor layer to resolve problem of conventional x-ray detector such as the direct detector and the indirect detector. To design the structure of ZnS(Ag)/a-Se detector, the penetrated energy spectrum and absorption fraction was estimated using MCNP 4C code. Also, we carried out the experiment to demonstrate the result of MCNP 4C code. Experimental results showed that the absorption fraction of $500{\mu}m$-ZnS(Ag) film was above 87%, 75% at 60 and 80 kVp. As a results, we can determined the thickness of suitable phosphor and the thickness of photoconductor.

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The study of Na Doping rate for application CsI:Na in the amorphous selenium (비정질 셀레늄 기반에서 CsI:Na 응용을 위한 Na의 조성비 연구)

  • Cha, Byung-Youl;Park, Ji-Koon;Kang, Sang-Sik;Lee, Kyu-Hong;Nam, Sang-Hee;Choi, Heung-Kook
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.11a
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    • pp.412-414
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    • 2003
  • This paper is about research of scintillator layer, which is used for Hybrid method to increase electric signals in a-Se, the material of Direct method. In case of the thermal evaporation, CsI has column structure which is an disadvantage as scintillator. But it decreases scattering of incident X-ray, has better Light output intensity than other scintillation materials. CsI was made by Thermal evaporation. The Doping material, Na, 0.1, 0.3, 0.5, 0.7g were added in each sample. Analysis of absorbed wavelength, PL(Photoluminescence), Light output intensity, SEM, and XRD analysis were performed to analyze optical characteristics. Doping rate of CsI:Na to use as scintillation layer in a-Se based detector could be optimized.

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Comparison of the I-V Characteristic as Various Composition ratio of Iodine in a-Se of $BrO_2/a-Se$ based Radiation Conversion Sensor ($BrO_2/a-Se$ 구조의 방사선 변환센서에서 a-Se에 첨가된 조성비 변화에 따른 I-V 특성 비교)

  • Choi, Jang-Yong;Park, Ji-Koon;Gong, Hyun-Gi;Ahn, Sang-Ho;Nam, Sang-Hee
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.11a
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    • pp.440-443
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    • 2002
  • Present1y the X-Ray diagnosis system is a real condition that is changing by digital ways in it's existent analog ways. This digital radiation detector is divided by the direct method and the indirect method. The indirect method of applied voltage has special qualities that the resolution is low than direct method by diffusion effect that happens. The conversion process ( radiation${\rightarrow}$visible ray${\rightarrow}$electrical signal of two times, has shortcomings that the energy conversion efficiency of electrical signal is low. The direct method has shortcomings that need strong electric fie1d to detect electrical signal efficiently. This research achieved to develop digital detector of the Hybrid method that have form that mixes two ways to supplement shortcoming of direct. indirect method. A studied electrical characteristic by Iodine's Mixture ratio change is added to selenium in the detector which has a multi-layer structure (Oxybromide + a-Se). There are 8 kinds of Manufactured compositions to amorphous selenium Iodine each 30ppm, 100ppm, 200 ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm by a doped photoconductor through a vacuum thermal evaporation method. The phosphor layer is consisted of Oxybromide ($BrO_2$) which uses optical adhesives multi-layer structure. The manufactured compositions calculates and compares Net Charge and signal to noise ratio measuring Photocurrent about Darkcurrent and X-ray. When doped Iodine Mixture ratio is 500ppm to the multi-layer structure (Oxybromide + a-Se), applied voltage of $3V/{\mu}m$, leakage current of compositions $2.61nA/cm^2$ and net charge value by 764pC/$cm^2$/mR then the best result appeared.

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Evaluation of Contrast-detail Characteristics of an A-Se Based Digital X-ray Imaging System (A-Se 기반 디지털 X-선 영상장치의 Contrast-detail 특성 평가)

  • Hyun, Hye-Kyung;Park, So-Hyun;Kim, Keun-Young;Cho, Hee-Moon;Cho, Hyo-Sung
    • Journal of the Korean Society of Radiology
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    • v.1 no.1
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    • pp.11-16
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    • 2007
  • In this study, we have performed contrast-detail analysis for an amorphous selenium(a-Se) based digital X-ray imaging system by using a contrast-detail phantom(CDRAD 2.0) to test its low contrast performance. The X-ray imaging system utilizes an 500-mm-thick a-Se semiconductor X-ray absorber coated over an amorphous silicon(a-Si) TFT(thin-film transistor) detector matrix with a $139mm{\times}139mm$ pixel size and a $46.7cm{\times}46.7cm$ active area. In the measurement of contrast-detail curves we first acquired X-ray images of the CDRAD 2.0 phantom at given test conditions(i.e., 40, 50, 60, 70, 80 kVp, and 16 mA.s), and then evaluated the contrast-detail characteristics of the imaging system from each phantom image by using an image quality factor called the image-quality-figure-inverse(IQFinv). The IQFinv values for the imaging system gradually improved with the photon fluence, indicating the improvement of image visibility: 24.4, 35.3, 39.2, 41.5, and 43.4 at photon fluences of $1.8{\times}105$, $5.9{\times}105$, $11.3{\times}105$, $19.4{\times}105$, and $29.4{\times}105$ photons/$mm^2$, respectively.

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Study on the effect of DSSC(Dye Sensitizer Solar Cell) Material on the electrical properties of Mercuric Iodide (염료감응형태양열 물질이 요오드화수은의 전기적 특성에 미치는 영향에 관한 연구)

  • Cho, Gyu-Seok;Park, Ji-koon;Heo, Seung-Wook;Song, Yong-keun;Han, Moo-Jae;Kim, Kum-Bae;Choi, Sang-Hyun
    • Journal of the Korean Society of Radiology
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    • v.11 no.6
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    • pp.525-529
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    • 2017
  • As a photoconductive material with a high X-ray sensitivity, many researches about mercury iodide has been carried out to substitute for amorphous selenium. However, it has many limitations in commercialization because of the high leakage current. In this study, we fabricated $HgI_2$ unit-cells with mixed silicon oxide($SiO_2$) and titanium oxide($TiO_2$) to reduce a high leakage current and we evaluated an electrical properties of the fabricated unit-cells. As a result, we confirmed that both mixtures were effective in reduing the leakage current of the $HgI_2$ and x-ray sensitivity were significantly increased in fabricated $HgI_2-TiO_2$ unit-cell.

Transport parameters in a-Se:As films for digital X-ray conversion material (디지털 X-선 변환물질 a-Se:As의 수송변수)

  • Park, Chang-Hee
    • Korean Journal of Digital Imaging in Medicine
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    • v.8 no.1
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    • pp.51-55
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    • 2006
  • The effects of Asaddition in amorphous selenium(a-Se) films for digital X-ray conversion material have been studied using the moving photocarrier grating(MPG) technique. This method utilizes the moving interference pattern generated by the superposition of the two frequency shifted laser beams for the illumination of the sample. This moving intensity grating induces a short circuit current, j$_{sc}$ in a-Se:As film. The transport parameters of the sample are extracted from the grating-velocity dependent short circuit current induced in the sample along the modulation direction. The electron and hole mobility, and recombination lifetime of a-Se films with arsenic(As) additions have been obtained. We have found an Increase in hole drift mobility and recombination lifetime, especially when 0.3% As is added into a-Se film, whereas electron mobility decreases with As addition due to the defect density. The transport properties for As doped a-Se films obtained by using MPG technique have been compared with X-ray sensitivity for a-Se:As device. The fabricated a-Se(0.3% As) device film exhibited the highest X-ray sensitivity out of 5 samples.

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