利用第一原理計算探討TMxCd1-xS (TM: Ti2+, Cr2+, Mn2+, Fe2+, Co2+, and Ni2+, x=0.03, 0.25)飛秒雷射與電光特性

In this thesis, the band structure and partial density of state (PDOS) of CdS, and TMxCd1-xS (TM = Ti2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, x = 0.03, 0.25) were analysed by first-principles calculations based on density functional theory. The band gap of 8-atoms CdS compound is 1.20 eV, and Cr2+0.25Cd0.75S compound has the smallest band gap of 0.71 eV. In addition, the band gap of 64-atoms CdS compound is 0.50 eV, and Cr2+0.03Cd0.97S compound also has the smallest band gap of 0.22 eV among all the TM doped into CdS compound. The analytic results from HOMO and LUMO reported Cr2+0.03Cd0.97S produced three defect levels which are dominated by Cr-3d and S-3p between valence-band and conduction-band of CdS. Therefore, the results told us Cr2+0.03Cd0.97S is the most suitable for the use as laser gain medium among Ti2+0.03Cd0.97S, Mn2+0.03Cd0.97S, Fe2+0.03Cd0.97S, Co2+0.03Cd0.97S and Ni2+0.03Cd0.97S.本論文係以第一原理(First-principles)計算基於密度泛函理論(Density functional theory, DFT)研究CdS與TMxCd1-xS (TM = Ti2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, x = 0.03, 0.25)能帶結構及部分能態密度，以探討過渡金屬濃度3%及25%置換Cd原子形成TM0.25Cd0.75S及TM0.03Cd0.97S晶體材料，所產生之缺陷能階及電子軌域分佈情形。在CdS模型使用8原子晶胞的部分，CdS能隙值經計算為1.20 eV，而Cr2+0.25Cd0.75S經計算具有最小之能隙為0.71 eV，且在CdS能隙間分裂產生由Cr-3d及S-3p主導之缺陷能階|0>及|-1>。而在CdS模型使用64原子晶胞的部分，CdS能隙值經計算為0.50 eV，而Cr2+0.03Cd0.97S具有最小之能隙為0.22 eV，並且在CdS能隙間分裂產生最多的缺陷能階|1>、|0>及|-1>。致謝....................................................I 摘要...................................................II Abstract..............................................III 目錄...................................................IV 表目錄.................................................VI 圖目錄................................................VII 第一章 緒論.............................................1 1.1 前言 ................................................1 1.2 研究動機與目的......................................2 1.3 論文架構............................................2 第二章 背景介紹與文獻回顧...............................4 2.1 雷射工作原理與裝置介紹..............................4 2.2 雷射種類與應用......................................5 2.3 過渡金屬Cr2+離子摻雜CdS晶體材料之雷射應用...........6 第三章 計算方法.........................................8 3.1 前言 ................................................8 3.2 Hohenberg-Kohn Theorem..............................8 3.3 Generalized Gradient Approximation (GGA)...........10 3.4贗勢(Pseudopotential)...............................11 第四章 8原子晶胞CdS基化合物之研究......................13 4.1 前言 ...............................................13 4.2 CdS與TM0.25Cd0.75S三元化合物模型建構 ...............13 4.3 CdS與TM0.25Cd0.75S三元化合物之能帶特性.............13 4.4 CdS與TM0.25Cd0.75S三元化合物電子結構特性分析 .......14 4.5 結論 ...............................................16 第五章 64原子晶胞CdS基化合物之研究.....................40 5.1 前言 ...............................................40 5.2 CdS與TM0.03Cd0.97S三元化合物模型建構 ...............40 5.3 CdS與TM0.03Cd0.97S三元化合物之能帶特性.............40 5.4 CdS與TM0.03Cd0.97S三元化合物電子結構特性分析 .......42 5.5 CdS與TM0.03Cd0.97S之HOMO與LUMO能階分析.............43 5.6 CdS與TM0.03Cd0.97S之能隙修正及光激發螢光光譜計算...44 5.7 結論 ...............................................45 第六章 總結論..........................................69 參考文獻 ...............................................7