二維材料石墨烯，是一種十分容易受到環境的水氣、氧氣以及其他雜質所影響的一種材料。當石墨烯轉移至舖有二氧化矽矽基板上時，基板表面所造成的不平整以及電子-電洞水窪 (electron-hole puddles) 會使石墨烯產生皺摺以及電荷分布不均等，進而造成很強的長程及短程散射, 以及應變引發之虛磁場 (pseudo magnetic field)效應 。為了降低石墨烯受到環境因素的影響，像是減緩基板以及大氣水氧造成電荷分布隨機參雜問題，我們分別在石墨烯底層和上層加入絕緣材料-六角氮化硼(h-BN)此種具有原子級平坦以及均勻電荷分布的特殊二維材料，集成為一堆疊結構, 類似凡德瓦異質結構(Van-der Waals heterostructure)，以期達到有效改善石墨烯電晶體的傳輸特性。
　　本文我們分別製作了石墨烯(G)、石墨烯/氮化硼(G/BN)以及氮化硼/石墨烯/氮化硼(BN/G/BN)三種不同結構的電晶體，並在G/BN以及BN/G/BN拉曼光譜中觀測到了G-peak的紅移，以及電性量測上遲滯現象的減緩等現象。並且在G/BN的結構中觀察到電洞載子高達20000cm2/V-s的優良傳輸性質。

Graphene is a two dimensional material which is one atom thick and, due to its high surface to volume ratio, is easily affected by environment such as atmospheric adsorptions and charged impurities incurred, unpredictable doping effect. For graphene flakes transferred onto SiO2/Si substrate, wrinkles and electron-hole puddles are present on graphene surface due to the surface roughness and charge traps in SiO2. It is known that the two-dimensional insulating hexagonal BN (h-BN) exhibits favorable physical properties such as atomic-level flat and charge-trap-free surface, which is widely used as the substrate or encapsulating layers for graphene to protect it against the environment, and is expected to improve transport and intrinsic properties of graphene.
In this thesis, we investigate the intrinsic and transport properties exhibited in both staked G/h-BN and h-BN/G/h-BN structures similar to van der Waals Heterostructures. The down-shift of both the Raman G-peak and charge neutrality point (CNP), and also the mitigation of hysteresis phenomenon are observed in the stacked structures in comparison with the system with graphene directly deposited on SiO2/Si substrate. We also achieve an extraordinary hole mobility as high as 20000 cm2/V-s in G/BN back-gate device.

目錄

第一章　緒論 1
1.1 半導體演進和所面臨的問題 1
1.2石墨烯以及二維材料的發現 3
第二章　石墨烯 5
2.1石墨烯的基本物性 5
2.1.1 石墨烯晶體結構 5
2.1.2 石墨烯電子能帶 8
2.1.3 石墨烯聲子能帶 12
2.1.4 如何打開石墨烯能隙 13
2.2石墨烯的基本電性 16
2.2.1 石墨烯傳輸特性 16
2.2.2 石墨烯散射源 18
2.2.3 石墨烯背向閘極電晶體電性分析 22
2.3石墨烯與氮化硼之凡德瓦異質結構 24
2.3.1氮化硼基本特性 24
2.3.2 石墨烯以氮化硼為基底電性傳輸 25
第三章　拉曼光譜分析 27
3.1 拉曼散射 27
3.1.1 拉曼散射基本原理 27
3.1.2 固態理論分析 32
3.2 拉曼檢測石墨烯 34
3.2.1 石墨烯在拉曼光譜的聲子散射 34
3.2.2 石墨烯層數判定 38
3.2.3 石墨烯的缺陷 40
第四章 石墨烯元件製備 43
4.1 石墨烯電晶體(graphene FET)操作原理 43
4.2 系統儀器介紹 44
4.2.1 黃光曝光機 (Optical lithography) 45
4.2.2 電子束微影 (Electron beam lithography) 46
4.2.3 反應式離子蝕刻 (Reactive Ion etching) 48
4.2.4 熱金屬蒸鍍 (Thermal evaporation) 49
4.3 雙層石墨烯的成長與分析 50
4.3.1化學氣相沉積反應機制 51
4.3.2 實驗準備 52
4.3.3 石墨烯成長 53
4.4 石墨烯元件製作流程 56
4.4.1基板備製 56
4.4.2石墨烯轉移 60
4.4.3 汲極、源極電極設計 63
4.4.4 石墨烯通道定義(isolation) 67
第五章 量測結果與分析 70
5.1 拉曼分析 70
5.1.1 石墨烯拉曼光譜 70
5.1.2 h-BN拉曼光譜 73
5.1.3 石墨烯與h-BN異質結構拉曼光譜 75
5.2 石墨烯電晶體背向閘極電壓量測 79
5.2.1 石墨烯背向閘極量測 80
5.2.2 石墨烯/氮化硼背向閘極量測 86
5.2.3 氮化硼/石墨烯/氮化硼背向閘極量測 90
5.2.4 存在於異質結構介面中的氣泡 94
第六章 結論 97
參考文獻 98

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