| Project/Area Number |
14550297
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Gifu University |
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Principal Investigator |
SHIMAKAWA Koichi Gifu University, Faculty of Engineering, Professor, 工学部, 教授 (60021614)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2002: ¥3,200,000 (Direct Cost: ¥3,200,000)
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| Keywords | chalcogenide glasses / X-ray digital detector / carrier diffusion / X-ray induced defect / photo-induced defect / image degradation / flat panel / electronic space charge / X-ray digital detector for Medical use / X-ray detector / photoinduced defect / photoinduced structural changes |
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| Research Abstract |
To obtain X-ray images directly for medical use, a new system without using X-ray films has been proposed (direct conversion from X-ray into free electrons and holes using chalcogenide glasses). A large area and real-time observations should be required in the new system. The following big problems should be overcome : (1) A signal intensity (sensitivity) decreases with X-ray exposures, and (2) The real time observations are limited owing to a response time.
In the present research project, the principal object is to understand the problem (1). It is well known that microscopic defects increase with visible light exposure in chalcogenide glasses. These light-induced defects lead to the decrease in sensitivity of optical devices. If the number of defect increases with X-ray exposure, sensitivity of X-ray images decreases, which is attributed to a decrease in collective efficiency of free electrons and holes induced by X-ray. Therefore, firstly, we should understand a correlation between defect creation arid sensitivity of X-ray images.
The following results have been obtained in amorphous selenium which is one of chalcogenide glasses: (1) Carrier collective efficiency decreases with X-ray exposure time. Time dependence of the decreases in sensitivity is empirically described by a stretched exponential function. (2) The photoconductivity is unchanged by X-ray-exposure. (3) Photoluminescence (PL) intensity is unchanged by X-ray exposure. The above results suggest that new defects are not induced by X-ray exposure.
Probably, trapping of electrons and holes induced by X-ray in deep localized states may affect carrier collection efficiency. These are also studied theoretically. Photo-structural changes have been also studied to understand these phenomena.
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