超低電洞濃度單層外延石磨墨烯及矽量子點之電傳輸特性之研究

Electronic Transport Properties of Ultralow-hole-density Monolayer Epitaxial Graphene and Si-MOS Quantum Dots

熊偉仁(Wei-Ren Syong)

指導教授 ： 梁啟德

國立臺灣大學/理學院/物理學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202001768

摘要

近年來探索二維材料及研究量子傳輸特性是熱門的話題。在此篇論文中，我們分別探討了成長在碳化矽超低電洞密度單層石墨烯及矽金氧半場效電晶體量子點的電傳輸效應。在量測這些元件的電傳輸特性時，我們發現有許多特別的物理特性，因此特別對這些特性進行解釋。
針對超低電洞密度單層石墨烯電性隨溫度及磁場的研究，我們發現此樣品在不同溫度區間有不同的磁阻趨勢。另外，對於在低溫下有顯著的磁阻比，使其在未來有作為低溫磁感測元件的應用。
而在矽金氧半場效電晶體量子點電性量測方面，我們觀察到除了量子點應有的庫侖震盪效應，通過溫度相依的測量也獲得了電壓與能量的關係。在不同次的降溫過程觀察到可重複的庫侖震盪結果確認了量子點的表現來自可調控靜電場的空乏閘極(depletion gates, DGs)。通過調變單一位障的高度，預期觀察到兩空乏閘極對位障的控制能力外，由於Si / SiO2系統的高度無序(high disorder)，使得在空乏電壓(VDGs)不足的情況下，兩位障轉為由雜質主導。另外，從數值模擬的結果觀察到，由於DGs形成的兩個位障的重疊，使量子點的化學位能嚴重受DGs的影響。此結果說明了元件幾何形狀對於電子點電性有相當嚴重的影響。透過我們的測量結果確認了Si-MOS量子點元件的可用性。此篇論文的研究可促進未來Si-MOS量子位元(qubit)的發展。

關鍵字

碳化矽超低電洞密度單層石墨烯 ； 磁阻 ； 矽金氧半場效電晶體量子點 ； 庫侖震盪效應

並列摘要

Recently, researching the physical properties of two-dimensional material and quantum transport of the electronic devices with nanoscale is a popular topic. In this thesis, we presented our work on ultralow-hole-density monolayer graphene on SiC and Si-MOS quantum dots separately. These studies will help us solve the problems that the quantum leak current seriously impacts the conventional transistors.
From the studies on the electronic properties of ultralow-hole-density epitaxial graphene with different temperatures and magnetic fields, we observed a crossover from NMR to PMR at T = 40 K in the magnetic field smaller than 0.3 T. In addition, the MR ratio is most significant at T = 120 K and becomes weaker at higher temperatures. It indicates that ultralow-hole-density monolayer graphene can be a good application in magnetic sensing devices at low temperature.
From the electronic properties of Si-MOS QD, the Coulomb charging effects were observed. The addition energy was extracted by the temperature-dependent measurements. Apart from this, the replicable results in thermal cycle ensured that the behavior of quantum dot is due to the electrostatic potentials of the depletion gates. By varying the height of single barrier, the abilities of each DG were investigated. However, the high level of disorder in Si/SiO2 system made the Coulomb oscillation be observed even if the VDGs are not negative enough to from the barriers. Finally, the numerical simulations presented that the overlap of two barriers, which strongly impacted the chemical potential of QDs. It explained that the geometry of the devices would influence the electronic properties of the devices. Our work confirmed the availability of the Si-MOS quantum dot device, and it would promote the development of qubits in the future.

並列關鍵字

ultralow-hole-density monolayer graphene on SiC ； magnetoresistivity ； Si-MOS quantum dots ； Coulomb oscillations

參考文獻

chapter 1

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