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タイトル: Theoretical Study on Electron States Floating in Internal Space of Condensed Matter Based on First-Principle Calculations
その他のタイトル: 第一原理計算に立脚した凝縮物質の内包空間に広がる電子状態の研究
著者: Matsushita, Yu-ichiro
著者(別言語): 松下, 雄一郎
発行日: 2013年3月25日
抄録: We report first-principles electronic-structure calculations that clarify the floating nature of electron states in covalent semiconductors. It is found that wave functions of several conduction- and valence-band states, including the conduction-band minima, do not distribute near atomic sites, as was taken for granted, but float in interstitial channels in most semiconductors. The floating states have a nearly-free-electron(NFE)-like character, and extend in the channels broadly without atomic-orbital characters. The electrostatic potential at the channels and the directions and shapes of the interstitial channels depend on the crystal symmetry so that mysterious variation of the energy gaps in silicon carbide (SiC) polytypes is naturally explained by considering the floating nature. In addition, we have found that the floating states are closely related to the anisotropy in effective masses in SiC. It has been found that most conduction-band minima have floating nature. The existence of the floating state comes from the internal space in the crystal structures, and non-spherical charge distribution. The substantial band-gap variation in SiC has been analyzed by an empirical parameter "hexagonality" for a half century. Yet, we have clarified that the parameter "hexagonality" is a misleading parameter. Instead, we have found that a new parameter "channel length", which represents the spatial extension of the floating state, is essential in describing the band-gap variation in SiC. In addition, we have performed the linear-combination-of-atomic-orbitals (LCAO) calculations and compared the results with those calculated by the plane-wave-basis set. It is found that the floating characters in the electron states are difficult to be pursued in the LCAO calculations. We have also examined the floating states in pressurized sp3-bonded materials. We have also found that the energy bands with floating character manifest different behavior from other bands with atomic-orbital character under the pressurized circumstances.
内容記述: 報告番号: ; 学位授与日: 2013-03-25 ; 学位の種別: 博士 ; 学位の種類: 博士(工学) ; 学位記番号: ; 研究科・専攻: 工学系研究科物理工学専攻
URI: http://hdl.handle.net/2261/55684
出現カテゴリ:021 博士論文
1132620 博士論文(物理工学専攻)

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