本論文探導過渡金屬硫族化物(TMDCs)場效電晶體(FETs)的低頻電雜訊(1/f雜訊)。在所有的電子元件中均有1/f雜訊存在，1/f雜訊會決定元件可以最小可以偵測或處理的訊號強度。單層TMDCs半導體是新穎的材料，可以應用在奈米元件及光電元件上。TMDCs薄膜有巨大的面積-體積比，因此TMDCs薄膜性質極易受到表面狀況的影響，而1/f雜訊也是一種表面性質。探討TMDC-FETs的雜訊成因並設法降低雜訊強度是一個重要的課題。
我們用實驗的方式觀察單層二硫化鉬(MoS2)及二硫化鎢(WS2)FETs中的1/f雜訊。MoS2 FETs的元件有高電子遷移率及歐姆接觸，藉由聚合物電解質(polymer electrolyte)，MoS2 的可以有效的調控到高載子濃度。使用聚合物電解質的MoS2 FETs，其雜訊可以用carrier number fluctuation 模型來描述。藉由比較使用和未使用聚合物電解質的MoS2 FETs元件，我們認為雜訊是來自於聚合物電解質和MoS2介面上的電陷阱。在WS2 FETs的元件中，在金屬及WS2接面形成蕭特基能障(Schottcky barrier)，期雜訊沒有符合一般雜訊強度正比於電流平方的關係，而雜訊強度隨載子數的關係則符合Hooge mobility fluctuation模型的描述。

Low-frequency (1/f) electrical noise in transition metal dichalcogenides (TMDCs) field-effect transistor (FETs) is investigated in this thesis. The 1/f noise exists in almost all electronic devices and it sets a limit on how small the signal can be detected and processed. Semiconducting monolayer TMDCs are emergent materials for nano-devices and optoelectronic applications. TMDCs films are highly sensitivity to surface and interface conditions due to huge surface-to-volume ratio and the 1/f noise is related to surface condition. Investigating the origin of the 1/f noise in TMDC-based devices in order to reduce its strength is an interesting topic.
In this thesis, the noise behavior of monolayer MoS2 and WS2 FETs are experimentally studied. In MoS2 FETs, high mobility and ohmic contact are achieved. With the help of polymer electrolyte (PE), MoS2 FETs can be effectively tuned to high carrier density region. The noise behavior of MoS2 FETs with PE-encapsulation is described by carrier number fluctuation model. By comparing the MoS2 FET with and without PE-encapsulation, we suggest that 1/f noise result from the interfacial traps between MoS2 and PE. On the other hand in WS2 FETs, Schottcky barriers are formed in the interface between WS2 and metal contacts. The low frequency noises show the 1/f spectrum but the dependence on current deviates from S_I∝I^2 relation. The carrier density dependence shows that the noise can be described by Hooge mobility fluctuation model.

Abstract i
Acknowledgements ii
Table of Contents iii
List of Figures vi
List of Tables xii

Chapter 1. Introduction 1
Chapter 2. Background Knowledge 5
2.1 Electrical Noise 5
2.1.1. The 1/f Noise Models 10
2.1.2. Mobility Fluctuation 11
2.1.3. Carrier Number Fluctuation 12
2.1.4. Carrier number fluctuation with correlated mobility fluctuations 19
2.2 Transition Metal Dichalcogenides 22
2.2.1. General Property of TMDCs 23
2.2.2. Synthesis and Characterization 26
2.2.3. Applications 30
Chapter 3. Experimental Methods 33
3.1 Noise Measurement 33
3.2 Polymer Electrolyte Gating Method 34
3.3 Device Fabrication 38
Chapter 4. Low Frequency Noise in MoS2 40
4.1 Review of Recent Research 40
4.2 Experimental Purpose 42
4.3 Device Characterization 42
4.4 Transport Properties 44
4.5 The 1/f Noise in PE-free and PE-encapsulated devices 46
4.6 The Noise Behaviors of the PE-encapsulated Devices 48
4.7 Summary 51
Chapter 5. Low Frequency Noise in WS2 52
5.1 Review of Recent Research 52
5.2 WS2 monolayers FET Characterizations 56
5.3 Transport Properties 56
5.4 The 1/f Noise in Room Temperature 58
5.5 Temperature Dependence of Transport Properties 61
5.6 Temperature Dependence of Noise Behavior 63
5.7 Summary 64
Chapter 6. Conclusions 65
Chapter 7. Future Works 68
Bibliography 71

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