近年來，陸陸續續有許多二維材料被發現，其中最受矚目的莫過於過渡金屬二硫族化物(TMD)，TMD的導電特性可以由電壓調變且能隙適中，除此之外具有獨特的光學特性、高載子遷移率等，在各方面應用都非常具有潛力。
對半導體材料進行摻雜是調控材料特性的主要方式，二維材料由於其厚度較薄無法使用離子佈值，因此多數是採用化學氣相沉積法成長材料時同時放入摻雜源，然而此摻雜方式為全區性的且無法精準控制濃度，在本論文中我們提出了一種可以達到選區摻雜又同時控制濃度的摻雜方式，以開有窗口的石墨烯作為遮罩保護覆蓋住的二硒化鎢區域，石墨烯惰性且結構穩定，可以控制只有窗口處之二硒化鎢被鉻原子摻雜與置換，且根據掃描穿隧式電子顯微鏡分析原子結構，鉻原子摻雜的濃度隨反應時間呈線性成長，這樣的實驗結果為局部改變二維材料特性提供了更多可能性。
另外，改善接觸電阻對於二維半導體也是一個重要議題，本論文提出了一個新穎的想法嘗試使用氫電漿移除二硒化鎢上層硫族原子層，之後直接鍍上金屬電極，使電極與過渡金屬層接觸形成鍵結，期望能消除穿隧能障，提升電子注入效率，改善接觸電阻。

Over the recent years, many two-dimensional (2D) materials have been explored, and transition-metal dichalcogenide (TMD) semiconductors have become an emerging research topic especially due to their tunable electronic and optical properties. Substitutional doping in TMD can manipulate the electrical, excitonic and optical properties through the variation of d-electron population. So far, the doping strategies in 2D materials are whole-area with the dopants embedded along with the growing process because the 2D thin layer is easily destroyed by ion implantation which is commonly used in 3D material. In this thesis, we demonstrate a post-growth site-selective Cr atoms doping and substituting the W atoms method in a mono-layer WSe2 via patterned graphene mask, which is chemically inert and effectively separated the spatial reaction. Meanwhile, the atomic characterization with scanning transmission electron microscopy shows that the Cr dopants concentration is controllable and increases linearly to the reaction time in the current doping approach.
However, the presence of large contact resistances remains a fundamental challenge in 2D semiconductors. In this thesis, we attempt to do defect engineering at the contact region by using hydrogen plasma treatment to reduce contact resistance. The plasma treatment selectively creates Se vacancies in the top Se atomic layer at the contact regions and the metal electrode directly bonds to transition metal W in WSe2 which eliminates the tunneling barrier and improves the contact resistance. Our findings suggest that defect engineering at the contact regions can be a feasible scheme to lower contact resistance and accomplish high-performance devices.

第 1 章 緒論...................................................... 1
1.1 半導體技術的進程.............................................. 1
1.2 傳統半導體的微縮與限制........................................ 2
1.3 低維半導體材料的發展.......................................... 5
1.4 低維半導體的侷限.............................................. 7
1.5 論文結構...................................................... 10
第 2 章 過渡金屬二硫族化物介紹.................................... 12
2.1 過渡金屬二硫族化物之組成與晶體結構............................ 12
2.2 過渡金屬二硫族化物之電子能帶特性.............................. 14
2.3 過渡金屬二硫族化物材料製備方法 ............................... 17
2.3.1 機械剝離法 (Mechanical exfoliation) ........................ 17
2.3.2 化學氣相沉積法 (Chemical vapor deposition, CVD)............. 18
2.4 材料檢測方式 ................................................. 21
2.4.1 拉曼散射頻譜 ............................................... 21
2.4.2 光致螢光光譜 ............................................... 24
第 3 章 半導體材料與金屬接觸接面探討.............................. 27
3.1 傳統半導體之金屬接觸特性 ..................................... 27
3.2 二維半導體之金屬接觸特性 ..................................... 30
3.2.1 過渡金屬二硫族化物與金屬接觸機制............................ 30
3.2.2 接觸金屬與費米能階釘扎的問題................................ 32
3.2.3 接觸電阻改善之方法一：金半接面弱耦合接觸.................... 36
3.2.4 接觸電阻改善之方法二：金半接面強耦合接觸.................... 37
3.3 蕭特基能障分析探討............................................ 40
第 4 章 元件製程與材料分析........................................ 43
4.1 二硒化鎢區域性鉻摻雜樣品製程.................................. 43
4.2 二硒化鎢與石墨烯材料成長 ..................................... 43
4.2.1 CVD 系統與流程.............................................. 43
4.2.2 拉曼散射檢測 ............................................... 46
4.2.3 光致螢光光譜檢測............................................ 49
4.3 製程設備...................................................... 49
4.4 鉻與硫之置換與分析 ........................................... 51
4.4.1 鉻與硫置換流程.............................................. 51
4.4.2 鉻置換樣品材料分析 ......................................... 55
4.4.3 鉻置換原理.................................................. 57
4.4.4 不同鉻摻雜濃度之材料分析 ................................... 57
4.4.5 鉻置換二硒化鎢電性分析...................................... 62
第 5 章 大面積金屬鍵電極製程與分析 ............................... 63
5.1 Janus WSSe 結構 .............................................. 63
5.1.1 電漿系統.................................................... 63
5.1.2 氫電漿反應機制.............................................. 64
5.1.3 Janus WSSe 材料檢測......................................... 65
5.2 大面積金屬鍵電極.............................................. 66
5.2.1 元件製作流程 ............................................... 66
5.2.2 製程設備.................................................... 67
5.2.3 預期電漿反應機制............................................ 69
5.2.4 電漿參數測試與材料分析...................................... 69
5.3 電晶體量測方法與系統.......................................... 75
5.4 電晶體量測結果與分析.......................................... 75
第 6 章 結論與未來展望............................................ 81

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