理學院: 應用物理所指導教授: 梁啟德劉泛鴻Liu, Fan-HungFan-HungLiu2017-03-062018-06-282017-03-062018-06-282015http://ntur.lib.ntu.edu.tw//handle/246246/276939本論文研究帶電載子在無序碳化矽石墨烯之傳輸特性，內容分為以下三個部分： 1.在多層碳化矽石墨烯中的狄拉克費米子加熱效應與電流尺度因子以及直接絕緣態-量子霍爾效應態的轉變: 我們展示了多層碳化矽石墨烯的磁阻量測結果，藉由維持樣品的環境溫度下增加源汲電流，狄拉克費米子加熱效應以及電流尺度因子進而在我們的樣品中被探討。利用零場磁阻當作是自體溫度計，我們可以得到不同源汲電流下，所對應的等效狄拉克費米子溫度；其關係式在零場時為TDF∝I^≈1/2。這個結果跟傳統二維系統中平台-平台轉變區域的結果一致。隨著磁場的增加，我們亦在縱向磁阻隨電流大小變化的圖形中，觀察到一個不隨電流變化的點，這個點同樣可以在縱向磁阻隨溫度高低變化的圖形中被觀察到，顯示出我們在多層碳化矽石墨烯中觀察到了直接絕緣態-量子霍爾效應態的轉變。儘管此現象需要更進一步的研究與了解，但綜合近期的實驗證據顯示，直接絕緣態-量子霍爾效應態的轉變在石墨烯中是個普遍存在的現象。 2.在多層碳化矽石墨烯中的局限效應以及電子-電子交互作用之探討: 在此篇論文中，我們探討了具有質量的載子在多層碳化矽石墨烯中，電子-電子交互作用以及局限效應對古典電導率的量子修正項。根據實驗結果證實，在多層碳化矽石墨烯中，若將谷際散射納入考量，則適用在傳統半導體構成二維系統中的擴散模型依然適用。更進一步來說，要更全面性地了解多層碳化矽石墨烯中的磁阻傳輸，我們必須將與磁場相關的電子-電子交互作用以及近藤效應納入考量。 3.利用比較有無氫原子插層的碳化矽石墨烯之熱載子傳輸現象，探討基板與石墨烯是否耦合的影響: 石墨烯電子元件能被工業化量產與利用的重要關鍵因素之一，在於是否能有效地控制石墨烯本身與環境之間的熱傳輸。欲使奈米元件在高頻中仍可正常運作，了解載子熱傳輸的機制是個相對重要的課題。在這篇論文中，我們藉由驅使有無氫原子插層的碳化矽石墨烯元件進入非平衡態，研究其熱載子在材料中的傳輸現象。有趣的是，我們證實了能量弛豫時間在有氫原子插層的碳化矽石墨烯中，比一般碳化矽石墨烯還要高兩個數量級，此現象建議我們若要使單層碳化矽石墨烯元件在高頻仍可正常運作，則要求外部需要有冷源可以與元件中的熱載子做有效的熱交換。The dissertation describes the studies of carrier transport behaviors in disordered epitaxial graphene on 6H-SiC (0001) and consists of three parts. 1.Dirac fermion heating, current scaling, and direct insulator-quantum Hall transition in multilayer epitaxial graphene: We have performed magnetotransport measurements on multilayer epitaxial graphene. By increasing the driving current I through our graphene devices while keeping the bath temperature fixed, we are able to study Dirac fermion heating and current scaling in such devices. Using zero-field resistivity as a self thermometer, we can determine the effective Dirac fermion temperature (TDF) at various driving currents. At zero field, it is found that TDF∝I^≈1/2. Such results are consistent with electron heating in conventional two-dimensional systems in the plateau-plateau transition regime. With increasing magnetic field B, we observe an I-independent point in the measured longitudinal resistivity ρxx which is equivalent to the direct insulator-quantum Hall (I-QH) transition characterized by a temperature-independent point in ρxx. Together with recent experimental evidence for direct I-QH transition, our new data suggest that such a transition is a universal effect in graphene, albeit further studies are required for obtaining a thorough understanding of such an effect. 2.Localization and electron-electron interactions in few-layer epitaxial graphene: This chapter presents a study of the quantum corrections caused by electron-electron interactions and localization to the conductivity in few-layer epitaxial graphene, in which the carriers responsible for transport are massive. The results demonstrate that the diffusive model, which can generally provide good insights into the magnetotransport of two-dimensional systems in conventional semiconductor structures, is applicable to few-layer epitaxial graphene when the unique properties of graphene on the substrate, such as intervalley scattering, are taken into account. It is suggested that magnetic-field-dependent electron-electron interactions and Kondo physics are required for obtaining a thorough understanding of magnetotransport in few-layer epitaxial graphene. 3.Hot carriers in epitaxial graphene sheets with and without hydrogen intercalation:role of substrate coupling: The development of graphene electronic devices produced by industry relies on efficient control of heat transfer from the graphene sheet to its environment. In nanoscale devices, heat is one of the major obstacles to the operation of such devices at high frequencies. In this chapter, I have studied the transport of hot carriers in epitaxial graphene sheets on 6H-SiC (0001) substrates with and without hydrogen intercalation by driving the device into the non-equilibrium regime. Interestingly, we have demonstrated that the energy relaxation time of the device without hydrogen intercalation is two orders of magnitude shorter than that with hydrogen intercalation, suggesting application of epitaxial graphene in high-frequency devices which require outstanding heat exchange with an outside cooling source.3502967 bytesapplication/pdf論文公開時間: 2015/7/23論文使用權限: 同意有償授權(權利金給回饋本人)碳化矽石墨烯熱載子電子交互作用弱侷限效應量子霍爾效應絕緣態霍爾態轉變epitaxial graphenehot carriere-e interactionweak localizationquantum Hall effectinsulator-quantum Hall transitionthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/276939/1/ntu-104-F98222050-1.pdf