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標題: | 以緊束縛近似法計算矽和二硫化鉬的能帶結構與電性質 Tight Binding Calculations of Silicon and MoS2 Band Structure and Electronic Properties |
作者: | Shuo-Fan Chen 陳爍帆 |
指導教授: | 吳育任(Yuh-Renn Wu) |
關鍵字: | 緊束縛近似法, Tight Binding, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 多年以來,半導體元件的推導大都基於泊松方程和電流平衡方程式的迭代,通常將材料視為完美晶格,如此一來能帶圖和相對應的能帶密度、載子有效質量和載子濃度都可以被寫成解析解。然而當金氧半場效電晶體的尺度到達原子等級,基於多體物理且運算量適當的模型將迫切需求,此模型必須將原子的週期位能效應考慮進薛丁格方程式的哈密頓算符中,並選取適當基底求解方程,在所有方法中,緊束縛近似法是最普遍的。在這篇論文中,我們將應用緊束縛近似法來計算矽奈米線的能帶和有效質量,以此研究不同寬度下,量子侷限效應對矽奈米線的影響,結果顯示量子侷限效應將增大材料的能隙和載子有效質量,且因於矽在不同方向的電子傳輸有效質量不同,量子侷限效應將改變傳導帶最低能態在倒置晶格空間中的位子。我們進一步將此模型應用於二硫化鉬上,二硫化鉬是一種具有很好的機械性質的二維材料,它可以承受很大的應力 (最高到12%),且它的奈米帶結構具有特別的表面特性,因此我們將緊束縛近似法應用在二硫化鉬和它的奈米帶結構上,來研究它的應力效應和表面性質,結果顯示外加拉伸應力會減小能隙和載子有效質量,然而主導價帶在倒置晶格空間中位子的改變,反而大幅增加電洞的有效質量。 For several decades, the semiconductor device theory was basically based on semi-classical model, where Poisson, drift-diffusion, and Schrodinger equation with effective mass or k.p method are solved to obtain the solution. The materials were often treated as perfect crystals, then the E-k relation and factors like density of state, effective mass and carrier density can all be written as analytical terms. However, as the dimensions of metal-oxide field effect transistors reach a few atomic scale, a model considering many-body physics with a reasonable time consumption is necessary. The new method needs to include the atomic potential into the Schrodinger Hamiltonian, then choose a suitable basis to solve the eigenvalue problem. Among all these approaches, the Tight Binding method (TBM) is the most popular. TBM directly uses the atomic orbital as the basis, and assumes that the potential is bonded tightly at the central atom. In this paper, we applied the tight binding method to silicon nanowires, and calculated the bandgap, effective mass and density of states. We studied the quantum confinement effect on the nanowires with different width, and compared to the infinite quantum well and the perfect crystal models. The results show that the quantum confinement effect will enlarge the bandgap and the carrier effective mass, and also rearrange the conduction band edge position in the k-space due to the effective mass difference between the lateral and perpendicular directions. Then we further applied our model to the novel 2D material. Molybdenum disulfide (MoS2) is a 2D material with good mechanical and chemical properties. It can endure a large strain (12%), and its nanoribbon structure has interesting edge properties. So we applied TBM to MoS2 and its nanoribbon to study the strain effects and edge states properties. The results show that the tensile strain can make the bandgap and the carrier effective mass smaller; however, the K-to-Gamma valley transition at the valence band edge gives it a larger hole effective mass. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/2668 |
DOI: | 10.6342/NTU201700233 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 光電工程學研究所 |
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