Investigation of Novel Semiconductor Layers on Post-Silicon Era Transistor Devices：Modeling and Simulation

可用於後矽時代的電晶體元件通道材料有兩大類，第一類為矽基合金材料如矽碳與矽鍺合金，其擁有成本低廉且製程完全相容，又可以有效提升元件效能的優勢。第二類為二維材料如單層過渡金屬硫族化物(Transition Metal Dichalcogenides, TMD)，可有效解決短通道效應(Short Channel Effect)，使元件可以繼續微縮。因此，本論文著重於研究上列兩類創新半導體通道材料在電晶體反轉層內載子能帶結構與遷移率的計算及量測。 對於第一類通道材料，我們利用考慮量子侷限效應之k.p方法，計算矽碳和矽鍺合金價電帶能帶結構，及其對應之量子化等效質量(quantization effective mass) 和狀態密度等效質量(density-of-states effective mass)，最後採用考慮各種散射機制的Kubo-Greenwood遷移率公式來研究合金效應對載子遷移率之影響。在元件量測方面，量測了於(110)矽基板上沉積高鍺濃度之矽鍺合金薄膜為通道之電晶體元件的電洞遷移率，並在和兩個通道方向分別施加垂直通道的拉伸應力和平行通道的壓縮應力，比較兩者間遷移率增益的變化。另外，我們量測以(001)、(110)和(111)三種矽基板上沉積鍺薄膜為通道的電晶體之電子遷移率及電流-電壓特性，並找出最佳的元件特性條件。 對於第二類通道材料，我們開發緊束縛(Tight Binding, TB)法擬合第一原理計算之能帶結果來研究TMD合金材料的精簡能帶結構，並進而計算其對應之重要物理參數如狀態密度等效質量、導電等效質量(Conductivity Effective Mass)與載子遷移率。此外，提出修正的等效質量近似(Modified Effective Mass Approximation, MEMA)能帶模型，此模型之優點是可以精準重現緊束縛法計算之導電帶(Conduction Band, CB)和價電帶(Valence Band, VB)結構，進而得到大幅縮短計算時間及不失準確度的好處。Novel channel material for transistor device used in the post-silicon age is classified into silicon-based alloy, e.g. silicon-carbon (Si1-xCx) and silicon-germanium (Si1-xGex) alloys which present low costs and compatible process and could effectively enhance transistor device performance, and 2D materials, such as single-layer transition metal dichalcogenides(TMD), which could effectively solve short channel effect and continuously shrink transistor device. This thesis therefore focuses on the investigation of carrier band structure and mobility in the transistor inversion layer of above two innovative semiconductor channel materials. For the first type of channel materials, k.p method of quantum confinement effect is utilized for calculating the band structure of Si1-xCx and Si1-xGex valence bands as well as the correspondent quantization effective mass and density-of-states effective mass. Finally, various scattering mechanisms for Kubo-Greenwood mobility calculation are applied to study the effect of alloy effect on carrier mobility. In terms of transistor device measurement, the hole mobility of transistor device, which have high germanium concentration silicon-germanium film deposited on (110) Si substrate as the channel, is measured. Besides, the and channels are applied vertical-channel tensile stress and horizontal-channel compression stress to compare the mobility gain changes. Furthermore, the electron mobility and current-voltage characteristics of transistors, which have germanium film deposited on (001), (110), and (111) Si substrates as the channel, are measured to find out the optimal device characteristics. For the second type of channel materials, Tight Binding(TB) method is used to fit First Principle band structure and is developed to study the simplified band structure of TMD materials and further calculate the correspondent physical parameters, e.g. density-of-states effective mass, conductivity effective mass, and carrier mobility. What is more, Modified Effective Mass Approximation(MEMA) band model, which could accurately present the conduction band(CB) and valence band(VB) structures calculated with Tight Binding method to further shorten the calculation time without losing the accuracy, is proposed.List of Tables v List of Figures vi Chapter 1 Introduction 1 1.1 Motivation 1 1.2 Literature Review 2 1.2.1 Silicon Based Materials 2 1.2.2 Transition Metal Dichalcogenide 8 1.3 Thesis Organization 17 References 19 Chapter 2 Subband Structure and Effective Mass in the Inversion Layer of a Strain Si-Based Alloy P-Type MOSFET 21 Abstract 21 2.1 Introduction 22 2.2 Theoretical Method 24 2.2.1 Subband Structure Theory 24 2.2.2 Effective mass model 25 2.2.2.1 Quantization Mass 25 2.2.2.2 Density of States Mass 26 2.3 Results and Discussions 26 2.3.1 Subband Structure of a Relaxed and Strained Silicon-Carbon Alloy Inversion Layer 26 2.3.2 Effective Mass Calculations 27 2.4 Summary 34 References 35 Chapter 3 Uniaxial stress effect and hole mobility in high-Ge content strained SiGe (110) P-channel metal oxide semiconductor field effect transistors 38 Abstract 38 3.1 Introduction 39 3.2 Device preparation and the mechanical uniaxial stress condition 41 3.3 Hole mobility measurement and calculation 42 3.3.1 Split C–V method 42 3.3.2 Kubo–Greenwood formula 43 3.4 Results and discussions 45 3.5 Summary 52 References 53 Chapter 4 Impact of Strain on Hole Mobility in the Inversion Layer of PMOS Device with SiGe Alloy Thin Film 56 Abstract 56 4.1 Introduction 57 4.2 Band structure of strained SiGe alloys 59 4.3 Hole mobility calculation of strained SiGe alloys 60 4.4 Results and discussions 62 4.5 Summary 73 References 74 Chapter 5 Metal Insulator Semiconductor Field Effect Transistors with Thin Strained Ge Film 78 Abstract 78 5.1 Introduction 78 5.2 Experimental 79 5.3 Results and Discussion 80 5.4 Summary 88 References 89 Chapter 6 How High can the Mobility of Monolayer Tungsten Disulfide be? 92 Abstract 92 6.1 Introduction 93 6.2 Calculation Method 95 6.3 Discussions and Results 97 6.4 Summary 106 References 107 Chapter 7 Compact Band Model for Transition-Metal Dichalcogenide Alloys 110 Abstract 110 7.1 Introduction 110 7.2 Calculation Method 113 7.2.1 Tight-Binding (TB) Method 113 7.2.2 EMA Band Model with the Second Nonparabolic Correction 114 7.2.3 Mobility Calculation for TMD alloy 116 7.3 Discussions and Results 119 7.4 Summary 138 References 139 Chapter 8 Summary and Future Work 142 8.1 Summary 142 8.2 Future Work 14