外延石墨烯於碳化矽基板上之電傳輸特性研究

Electronic Properties of Epitaxial Graphene Grown on SiC

劉玠沂(Chieh-I Liu)

指導教授 ： 梁啟德

國立臺灣大學/理學院/應用物理研究所/博士(2017年)

https://doi.org/10.6342/NTU201701356

摘要

生長於碳化矽基板上之外延石墨烯具備優異的材料性質，因此被期待可用來發展新一代的電子元件。此篇論文主要研究外延石墨烯的電傳輸特性，首先介紹石墨烯基本特性與研究相關之背景知識，樣品的製作方法與儀器設備皆有詳細說明。
實驗結果部分將會分成三個主題。第一個主題研究在外延石墨烯上電荷捕捉(charge trapping)、弱局域效應(weak localization)與電子-電子交互作用(electron-electron interactions)。電荷捕捉的能量ΔE在不同樣品之間的變化可從196 meV到34 meV，從實驗結果顯示樣品遷移率越高ΔE越小，說明樣品品質的重要性。藉由研究弱局域效應，可了解量子干涉所需的特徵長度。另外，利用弱局域效應的修正量和零磁場下的電阻值皆可以當作計算有效電子溫度的溫度計。在高溫範圍，利用霍爾斜率(Hall slope)和對數溫度關係圖，可有效探討電子-電子交互作用。
第二個主題研究在單層外延石墨烯的變程跳躍(variable range hopping, VRH)和非線性傳輸。在線性區域，使用RCDA (resistance curve derivative analysis)方法可決定樣品是屬於Mott VRH或Efros-Shklovskii (E-S) VRH。實驗觀察到在非線性區域，電導顯現出與電壓有強烈相依性的現象，實驗數據可透過理論模型準確模擬。
最後一個主題為Parylene C薄膜封裝的初步結果，結果顯示Parylene C與石墨烯表面的微弱作用力使之成為合適的封裝材料。除此之外，表面電導(surface conductance)量測為大面積石墨烯樣品提供了快速且方便途徑。將樣品暴露於環境控制箱(environmental chamber)之後，載子濃度連同其他物理量隨之改變，因此，Parylene C與石墨烯表面的附著力仍需做進一步改進。

關鍵字

石墨烯 ； 外岩石墨烯 ； 弱局域效應 ； 電子-電子交互作用 ； 變程跳躍

並列摘要

The remarkable properties of epitaxial graphene (EG) growth on SiC shows promising prospects of application in future electronics. This dissertation focuses on the electronic properties of EG. I begin with a basic knowledge of graphene along with necessary background for the research. There will be demonstrations of sample preparations and experimental setups.
The experimental results described in this thesis are divided into three parts. The first topic involves charge trapping, weak localization and electron-electron interactions on EG. Activation energies ΔE for charge trapping in epitaxial graphene ranging from 196meV to 34meV. It is shown that ΔE decreases with increasing mobility indicates the importance of sample quality. Different scattering channels can be recognized by studying the weak localization. Also, it is found that both the zero-field resistance and the WL correction term can be used as reliable thermometers. In the high-temperature regime, a logarithmic temperature (lnT) dependence of the Hall slope is a good physical quantity which allows us to investigate electron-electron interactions.
The study on variable range hopping (VRH) and non-linear transport in monolayer epitaxial graphene is described in the second topic. The resistance curve derivative analysis method can be used to determine whether Mott VRH or Efros-Shklovskii VRH is the dominant transport mechanism in the linear regime. In the non-linear regime in which the conductance shows a strong dependence on voltage, it is found that the experimental results can be well described by existing theoretical models.
The last topic describes the preliminary results on Parylene C encapsulation. The weak interactions on the interface of Parylene C/graphene shows Parylene C is a suitable encapsulated material. Besides, surface conductance measurement provides a faster and convenient way to characterize longitudinal resistivity of large-area graphene samples. The variations in quantities after exposing to environmental chamber and ambient air shows room for improvement in adhesion between Parylene C and graphene.

並列關鍵字

graphene ； epitaxial graphene ； weak localization ； electron-electron interactions ； variable range hopping

參考文獻

Chapter 1

[7] P. R. Wallace, Phys. Rev. 71, 622 (1947).

[8] C. Virojanadara, M. Syvajarvi, R. Yakimova, L. I. Johansson, A. A. Zakharov, and T. Balasubramanian, Phys. Rev. B: Condens. Matter Mater. Phys. 78, 245403 (2008).

[16] W. Norimatsu and M. Kusunoki, Phys. Chem. Chem. Phys. 16, 3501 (2014).

[1] N. Ashcroft and N. Mermin, Solid State Physics (1976).