| Project/Area Number |
05640369
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | Tohoku University |
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Principal Investigator |
KATAYAMA-YOSHIDA Hiroshi Dept.of Physics, Tohoku University, Assoc.Professor, 理学部, 助教授 (30133929)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1994: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1993: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | ab intio Molecular Dynamics / Electronic Excitation / Amorphous / Negative Effective U / Dangling Bonol / 水素化アモルファスシリコン |
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| Research Abstract |
The nature of the isolated dangling-bonds (D) in amorphous silicon (a-Si), hydrogenated amorphous silicon (a-Si : H) and crystalline silicon (c-Si) are investigated using ab-initio molecular-dynamics simulation. We find that the bistability of dangling-bonds at sp^3- and sp^2-like configuration which exhibit a large lattice-relaxation in all cases. Neutral dangling-bond at sp^3-like configuration shows negative effective-U nature with large lattice-relaxation. Therefore the neutral dangling-bond (D^0) is unstable at the thermal equilibrium and disproportionate into negatively- and positively-charged dangling-bond ; 2D^0 --> D^- + D^+. On the other hand, neutral dangling-bond at sp^2-like configuration shows positive effective-U nature, and positively-, neutrally-, and negatively-charged dangling bonds appear with increasing the chemical potential.
These bistabilities in dangling-bonds with the positive and negative effective-U nature are related to the microscopic mechanism of the X-ray-irradiation-enhanced crystallization in amorphous silicon in which the vacancy-interstitial-pair formation by X-ray irradiation reduces the formation energy of the vacancy and enhances the crystallization. We also find that the negative effective-U nature of the dangling-bond at sp^3-like configuration is related to the origin of Staebler-Wronski effect in which the neutral dangling-bonds of positive effective-U at sp^2-like configuration are created by the recombination-enhanced defect-reaction with the exposure to the visible light. Our prediction can explain all available experimental data very reasonably.
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