由於二維材料具有原子尺度的厚度和獨特的物理特性，它引發了大家對於二維材料的廣大興趣。因為二維材料具有很大的表面積與側面積比，大多的文獻皆使用top contact結構，載子到達電極除了會遇到蕭特基能障以外，還有凡得瓦力所產生的穿隧能障，使得電晶體的特性下降。本論文除了探討元件隔離先後順序對二硒化鎢電晶體的影響外，也將探討使用多層石墨烯當源極/汲極對電晶體特性的影響，實驗結果顯示若先對二硒化鎢進行元件隔離，電晶體會具有較佳的特性但也因光阻等殘留物的殘留具有較大的差異性，在氫氣環境下退火可以有效地去除殘留物，但因金屬鈀會與氫氣反應使得蕭特基能障增加得到反效果。如果我們使用p摻雜多層石墨烯當源極/汲極，二硒化鎢在靠近源極/汲極的界面為多層能隙較小、p摻雜使得多層石墨烯的費米能階較接近二硒化鎢的價帶和我們可以透過閘極偏壓的方式改變石墨烯的費米能階來減小蕭特基能障，綜合上述p-doped-MLG-WSe2電晶體具有較高的電流、較高的電洞遷移率和較低的接觸電阻。

Two dimensional (2D) materials have been received an enormous amount of interest owing to their atomic scale thickness and unique physical properties. Because of the large surface/edge ratio in 2D materials, most of the published literatures use the top metal contact scheme. Besides the Schottky barrier, there is an additional tunneling barrier exists at contact interface due to the vdW gap. It limits the carriers traveling to the metals and degrades the transistors performance. In this work, we discuss the influence isolation sequence of the transistors; and source/drain engineering by using multilayer graphene (MLG). The transistors have better performance when we isolated the WSe2 first, though the photo resist residues in contact interface resulting in worse variations. We might remove part of the residues by annealing the sample in hydrogen environment. However, the performance turns out to be degraded since the reaction between Pd metal and hydrogen actually increases Schottky barrier between them. For the source/drain engineering study using MLG serves as S/D, the few-layer WSe2 forms at junction region resulting a small bandgap and Schottky barrier at the MLG-WSe2 interface. The p-doping effect effectively modulate the graphene Fermi level and therefore reduce the Schottky barrier. The Fermi level of graphene could be shifted by electrically gating as well. As the result, the p-doped-MLG-WSe2 transistors have better Ion, mobility, and smaller contact resistance.

致謝 i
摘要 ii
Abstract iii
目錄 v
圖目錄 viii
表目錄 xi
第1章 序論 1
1.1 研究背景 1
1.2 研究動機 3
1.3 論文內容大鋼 3
第2章 文獻回顧 4
2.1 二維材料(Two-Dimensional Materials) 4
2.1.1 過渡金屬硫化物(TMDs) 5
2.1.2 二硒化鎢(WSe2) 7
2.1.3 石墨烯(Graphene) 8
2.2 二維材料電晶體 10
2.2.1 過渡金屬硫化物電晶體操作極性 11
2.2.2 Contact issue of 2D devices 12
2.2.3 The Y Function Method (YFM) 14
2.3 物性分析 15
2.3.1 拉曼光譜 15
2.3.2 光激螢光光譜 16
2.3.3 穿透式電子顯微鏡分析(Transmission Electron Microscopy Analysis) 17
第3章 材料分析與元件製程 19
3.1 元件物性分析 19
3.1.1 拉曼分析(Raman Analysis) 20
3.1.2 光激螢光分析(Photoluminescence Analysis) 21
3.1.3 穿透式電子顯微鏡分析(Transmission Electron Microscopy Analysis) 22
3.2 元件製備流程 24
3.2.1 Source/Drain與閘極金屬沉積方法 25
3.2.2 元件隔離(Isolation) 28
3.2.3 閘極氧化層二氧化鉿(HfO2)沉積 29
3.2.4 Contact Hole Opening 30
第4章 元件電性結果與討論 32
4.1 電晶體I-V特性 32
4.1.1 Isolation last versus isolation last Pd-WSe2 Devices 33
4.1.2 氫氣環境下退火的Pd-WSe2電晶體I-V特性 37
4.1.3 p-doped Multilayer graphene WSe2電晶體I-V特性 39
4.2 Contact resistance討論 42
第5章 總結與未來展望 47
5.1 結論 47
5.2 未來展望 48
參考文獻 49

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