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研究生:林彥成
研究生(外文):Yen-Cheng Lin
論文名稱:硒化鉍薄膜成長、特性與拓樸性質之實驗研究
論文名稱(外文):Experimental studies on the growth, characterization and topological properties Bi2Se3 thin film
指導教授:張顏暉張顏暉引用關係
指導教授(外文):Yuan-Huei Chang
口試委員:林敏聰陳永芳黃斯衍
口試委員(外文):Minn-Tsong LinYang-Fang ChenSsu-Yen Huang
口試日期:2015-07-07
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:應用物理所
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2015
畢業學年度:103
語文別:英文
論文頁數:56
中文關鍵詞:硒化鉍薄膜
外文關鍵詞:Bi2Se3thin film
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拓墣絕緣體為近年來發現的新穎材料,其有著邊緣或表面能導電的特性與內部絕緣的特性。近年來主要成長硒化鉍(Bi2Se3)薄膜是由分子束磊晶(molecular beam epitaxy , MBE)的方式,然而此方式花費成本太高,理想的是有更簡單且經濟的方式製作樣品。
在此篇論文中,我們使用物理氣化沈積(physical vapor deposition, PVD)方式來製備硒化鉍薄膜成長在藍寶石基板(Al2O3)上,用此方式我們能在藍寶石基板長出1公分 1公分大面積的薄膜,此方式能將薄膜製備得更簡單且花費更低。物理氣化沈積方法是將硒化鉍粉末和藍寶石基板放入石英管中且用機械幫浦將石英館內壓力降低,我們將硒化鉍的粉末至於高溫爐中央,而藍寶石基板置於距離硒化鉍粉末15公分的下游處,我們使用500 或530 為硒化鉍氣化的溫度,沈積區基板溫度控制在300 或350 ,在成長過程中,環境壓力控制在 5X10^(-3)torr。
我們利用原子力顯微鏡(atomic force microscopy, AFM)來量測膜厚,結果顯示在不同的溫度與時間參數下,膜厚從8到60奈米。我們用X光繞射分析(X-ray diffraction, XRD)分析晶格結構,結果顯示我們成長的薄膜有很好的晶格結構,在Phi角掃描的結果顯示,我們的薄膜有六重對稱,其代表薄膜成長方式與外延模式是區域匹配的(domain matching epitaxy mode);由X光能譜分析儀(energy-dispersive X-ray spectroscopy, EDS)分析薄膜成份,結果顯示鉍與硒的比例很接近2比3;由X射線光電子能譜儀(electron spectroscopy for chemical analysis, ESCA)分析硒與鉍的鍵結能量;由穿透式電子顯微鏡(Transmission Electron Microscopy, TEM)觀測薄膜排列結構,結果顯示我們成長的薄膜為層狀結構且每一五層結構的厚度為0.94奈米。
我們使用厚度為30奈米的薄膜製作成Hall bar的裝置來量測電性,量測結果顯示,在溫度從2 K到300 K間,載子濃度(carrier concentration)介於1.07X10^(19)/cm^3 與 1.09X10^(19)/cm^3之間,電阻率隨溫度的量測結果顯示,在溫度為4.5 K時發生金屬性與絕緣體性的轉換,電子遷移率(mobility)在溫度為2 K時為940,此量值高於脈衝雷射蒸鍍系統(Pulsed laser deposition, PLD)製備的薄膜18倍。磁阻量測顯示,弱反局部化(Weak anti-localization)效應出現在低磁場下,此結果顯示我們製備的薄膜有拓墣絕緣體的性質存在,用Hikami-Larkin-Nagaoka (HLN) 式子分析結果顯示,我們的薄膜有一個表面通道在導電且去相位長(dephasing length)為640奈米。


Topological insulators are a new kind of innovative materials that have an insulating behavior in the bulk but a conducting behavior at the surface. Up to date, most of the high quality bismuth selenide (Bi2Se3) thin films were grown by using molecular beam epitaxy (MBE). This method, however, is too expensive and it is desirable to have a simpler and more affordable way of making the samples.
In this work, the physical vapor deposition (PVD) method was used to grow large area Bi2Se3 thin films with size of cm2, on sapphire (Al2O3) substrates. This method has the advantage that it is simple and inexpensive. For the PVD growth the source powder and the substrate were placed in a quartz tube that is put inside a furnace and a mechanical pump is connected to the quartz tube to reduce the pressure in the tube. During the growth, Bi2Se3 powder was placed at the center of furnace, Al2O3 substrate was placed 15 cm away from the source powder, the source temperature was kept at either 500 or 530 , the substrate temperature was kept at either 300 or 350 , and the environment pressure was fixed at 5X10^(-3)torr.
Atomic force microscopy (AFM) measurements indicate that, depending on growth durations, the thickness of Bi2Se3 thin films varies from 8 nm to 60 nm, X-ray diffraction (XRD) indicate that the films were of good crystalline quality. The six-fold symmetry of the phi-scan indicates that the growth mode is domain matching epitaxy mode. The energy-dispersive X-ray spectroscopy (EDS) measurements confirmed that the ratio of Bi and Se were 2 to 3 and the electron spectroscopy for chemical analysis (ESCA) showed that the binding energies are that for Bi and Se. Transmission Electron Microscopy (TEM) measurements indicate that the film had a layer by layer structure and the thickness of each quintuple layer is 0.94 nm.
For the electrical measurement, the film with thickness of 30 nm was made into a Hall pattern. The carrier concentration in this sample is found to be between 1.07X10^(19)/cm^3 and 1.09X10^(19)/cm^3 from T=2k to T=300K and metal insulator transition was found to occur at 4.5 K. The mobility of the sample is 940 cm2/Vs at 2 K, about 18 times larger than similar film grown by using pulsed laser deposition. Weak anti-localization (WAL) was found at low magnetic field in the magneto-resistivity measurement, showing that the sample has the property expected for a topological insulator. By fitting the data with the HLN formula we found that the surface conduction occur only in one surface of the sample and the dephasing length of the electron is 640 nm.

Contents
Chapter 1 Introduction
1.1 Background…………………………………………………………………………..1
1.2 Bismuth selenidev (Bi2Se3)……………………………………………………….....2
1.3 The motivation……………………………………………………………..……….4
Chapter 2 Theory
2.1 Drude model…………………………………………………………………………5
2.2 Hall effect……………………………………………………………………………7
2.3 Weak localization………………………………………………………………….…9
2.4 Weak anti-localization...............................................................................................10
Chapter 3 Principles of experimental apparatus
3.1 X-ray Diffraction (XRD)…………………………………………………………...12
3.2 Atomic force microscopy (AFM)…………………………………………………..13
3.3 Electron Spectroscopy for Chemical Analysis (ESCA)……………………………15
3.4 Scanning electron microscopy (SEM) & Energy-dispersive X-ray spectroscopy
(EDS)……………………………………………………………………………….17
3.5 Transmission electron microscopy (TEM)…………………………………………19
Chapter 4 Experimental methods
4.1 Procedures of growing Bi2Se3 thin films on Al2O3 substrates………………….…21
(a) Preparation prior to Bi2Se3 thin film growth…………………………………21
(b) The growth of Bi2Se3 thin film by physical vapor deposition………………..21
4.2The procedures of hall device production…………………………………………..22
(a) Etching the Hall bar pattern………...…………………………………………22
(b) Thermal evaporation metal contact……………………………………………23
Chapter 5 Results and discussion
5.1 Thickness of Bi2Se3 thin films……...………………...…………………….………25
5.2 Analysis result of Bi2Se3 thin films……………..………………………….………32
5.2.1 The structure of different growth condition………………….………………...…32
5.2.2 The TEM result of Bi2Se3 thin film……………...……………………………….38
5.2.3 The component of Bi2Se3 thin film……………………………………………….39
5.3 Electrical measurement………………...………………………………….…..…...42
5.3.1 The resistivity measurement……………………...…………………………....…43
5.3.2 The carrier concentration and mobility………...…………….…………………..45
5.3.3 The magneto-transport……………………………………………………………47
Chapter 6 Conclusion………………………………………………………..……52
References…………………………………………………………………………...54






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