III-V Nanowire Epitaxy for Ultimate Logic Device Scaling

This Ph.D study focuses on how to grow high yield and good quality InAs nanowires in a controllable way by selective area epitaxy on Si (111) substrate for vertical gate-all-around MOSFET applications. We first identify the challenge of direct epitaxy of InAs on Si. Gallium is found to be beneficial for the nanowire yield improvement and a new method using InGaAs nucleation layer is proposed. The distribution of planar defects in InAs nanowires are thoroughly analyzed. A quantitative method to extract their frequency is developed by using easily accessible lab X-ray diffractometer. By using this new characterization method, we explore how to control the polytypism in InAs nanowires by growth parameters. As a result, nearly pure wurtzite phase InAs nanowires are obtained. Finally, the mechanism of planar defect formation is studied in detail, which is closely related to surface reconstruction transition.Acknowledgement i Abstract iii Samenvatting v Contents vii Abbreviations xii List of Symbols xiv Chapter 1: Introduction 1 1.1 Logic device scaling and III-V nanowires 1 1.1.1 MOSFET scaling and challenge 1 1.1.2 SCEs and gate-all-around (GAA) MOSFET 3 1.1.3 High mobility III-V materials and their integration 4 1.1.4 Vertical Geometry 6 1.2 Epitaxy 8 1.2.1 Basic concepts of vapor phase epitaxy (VPE) 8 1.2.2 Epitaxy Methods 11 1.2.3 General challenges of III-V epitaxy on Si: 13 1.2.4 Selective area epitaxy (SAE) 16 1.3 Synthesis of vertical Nanowires for next generation logic devices 17 1.3.1 Top-down approach 17 1.3.2 Bottom up approach 19 1.4 III-V NW epitaxy on Si 19 1.4.1 VLS and non-catalytic methods 19 1.4.2 State of the art of III-V NW SAE 22 1.5 Crystal structure of III-V NWs 25 1.5.1 Zinc-blende and Wurtzite Structure 25 1.5.2 Phase intermixing phenomenon (polytypism) and planar defects 27 1.6 Motivation of the thesis and organization 29 Reference 32 Chapter 2: Experimental Details 55 2.1 Experimental Details of III-V NW growth 55 2.1.1 Template preparation: 55 2.1.2 III-V NW growth 58 2.2 Characterization Method 60 2.2.1 Diffraction methods 60 2.2.2 Transmission electron microscope (TEM) 65 2.2.3 Electron dispersive X-ray spectrum (EDX) 67 2.2.4 Scanning electron microscope (SEM) 67 2.2.5 Time-of-flight secondary ion mass spectrometry (TOFSIMS) 68 2.2.6 Atomic force microscope (AFM) 69 2.3 Summary 70 Reference 71 Chapter 3: InAs nanowires nucleation on Si (111) surface 73 3.1 Challenge of InAs NW SAE on clean Si (111) surface 73 3.1.1 Direct SAE of InAs NW on Si (111) surface 74 3.1.2 Si (111) surface before NW growth 77 3.2 Effect of Gallium incorporation on InAs NW nucleation 80 3.2.1 Ga impact on NW yield 80 3.2.2 Direct observation InAs NW SAE assisted by Ga contamination 85 3.2.3 Discussion on the role of Ga 89 3.3 Novel growth method of InAs NWs on Si by using InGaAs nucleation layer 94 3.4 Summary 96 Reference 97 Chapter 4: Characterization of polytypism in InAs NWs 104 4.1 InAs NWs sample description 104 4.2 Crystal structure analysis by HRTEM 107 4.2.1 PDs in InAs NWs 108 4.2.2 Crystal structure of irregular blocks 112 4.3 Characterization of PDs using XRD 113 4.3.1 XRD results 114 4.3.2 Quantitative model to extract PD frequency from XRD Bragg angle 119 4.4 Summary 122 Reference 124 Chapter 5: Mechanism of Polytypism formation in InAs NW SAE 128 5.1 Control of polytypism in InAs NW SAE 129 5.1.1 Effect of growth parameters 129 5.1.2 Toward pure phase InAs NW SAE 133 5.2 The origin of PDs in III-V NWs: General understanding 135 5.3 InAs (111) B Surface: the variable 138 5.3.1 Surface reconstruction 138 5.3.2 Homoepitaxy on InAs (111)B 141 5.4 Impact of Surface reconstruction on NW polytypism 145 5.4.1 Surface reconstruction transition model 145 5.4.2 Relationship between hexagonality and surface reconstruction 149 5.5 Summary 153 Reference 154 Chapter 6. Summary and Outlook 165 6.1 Summary 165 6.2 Outlook of InAs NW SAE R&D for vertical GAA MOSFET 167 Reference 171 Appendix 172 A.1 Impact of oxide layer in active area for InAs NW SAE 172 A.2 XRD peaks on NW length and density 176 A.3 The mathematical proof of 1D randomly disordered layers model containing three elements 180 A.4 Growth of ZB-phase InAs NWs 183 A.5 Electrical properties of InAs NWs with different hexagonality 185 Reference 190 Publication List 192nrpages: 193status: publishe