本實驗主要在探討不同厚度下使用摻雜原子百分比5% 鈣(Ca)離子濃度鐵酸鉍(BiFeO3, BFO)薄膜所表現出的光伏效應，藉由各項儀器來觀察BFO薄膜的差異性，來推測影響光伏效應的可能原因與機制。
本實驗以磁控濺鍍法(RF-sputter)成長BFO薄膜以及上下電極於矽基板Si(100)上。利用場發射電子顯微鏡來觀察厚度是否符合實驗所設定，X光繞射儀來分析薄膜的結晶特性，X光反射儀與原子力顯微鏡觀察粗糙度，鐵電量測儀量測電滯曲線，使用405nm Laser量測光伏效應。
由BFO薄膜的XRD圖譜僅發現BFO ( 0 0 1) 與(0 0 2) 繞射峰，可知BFO薄膜具有良好的結晶性及明確的優選方位。由XRD圖譜也看出，隨著厚度增加，薄膜有應力釋放的現象。光反射儀與原子力顯微鏡結果顯示隨著厚度增加粗糙度也跟著變化，但是變化不大。電滯曲線的結果顯示，隨厚度的增加，薄膜的極化值有下降的趨勢。同時，光伏效應亦隨著膜厚增加而逐漸降低。當應力產生變化，晶格變形量改變，將導致偶極矩改變，影響薄膜內電場，致使效率明顯改變。此外，當厚度增加至100及150奈米時，上下電極間距大幅拉長，致使電子收集效率降低，以及正負電荷對在薄膜中移動時發生再結合或是散射現象機率提升，掩蓋薄膜光伏效應的呈現。

In this experiment, the photovoltaic effect with different film thickness of 5% Ca doped BiFeO3 thin films were investigated. The probable physical mechanism were carried out many different measurements which may affect the efficiency of the photovoltaic effect. The specimen of BFO thin films and the electrode were all deposited on Si(100) by RF magnetron sputtering. First, we grew LaNiO3 on Si(100) at 450 . Second, The 5% Ca doped BiFeO3 films were deposited on LaNiO3. Third, we deposited Pt or AZO to do measurements, respectively. Film thickness was estimated by SEM and X-ray reflectivity. Film crystallinity was carried out by X-ray diffraction measurement. The morphology was measured by atomic force microscope and X-ray reflectivity. The hysteresis loop was performed by TF-2000 and the photovoltaic effect were measured by 405 nm laser.
BFO was (100) highly preferred along Si (100) substrate from X-ray diffraction measurement. BFO film strain relax as film thickness increase, hence the diffraction peak position shift more close to the expected bulk value. The surface roughness, which was carried out by AFM and X-ray reflectivity has little increase as film thickness thicker. The hysteresis loop showed that the polarization slow down as the film thickness increased. The photovoltaic effect also slow down as the film thicker.
The BFO built-in electric field affect the efficiency of photovoltaic effect. As the film thickness increased to 100 nm, the strain relax caused built-in electric field become weaker and the probability of electron and hole recombined increase due to distance between two electrode; therefore, the efficiency of photovoltaic hidden.

目錄
致謝 I
摘要 II
Abstract IV
目錄 VI
第一章 序 論 1
1-1 前言 1
1-1-2鐵電薄膜 1
1-2研究動機 2
第二章 文獻回顧 5
2-1鐵電材料簡介 5
2-2極化與漏電流 6
2-2-1極化機制 6
2-2-2漏電流機制 10
2-3 鐵酸鉍(BiFeO3) 11
2-3-1鐵電材料電滯曲線(hysteresis loop) 15
2-3-2光伏原理 17
2-3-3 壓電特性 22
2-4 LaNiO3下電極 23
2-5 AZO上電極 24
第三章 實驗方法與步驟 25
3-1實驗材料 25
3-1-1 Silicon wafer (001) 25
3-1-2製備薄膜所需氣體 25
3-1-3實驗相關藥品 26
3-1-4 金屬靶材 26
3-2實驗設備 28
3-2-1射頻磁控濺鍍系統(RF magnetron sputtering system) 28
3-3實驗製程 31
3-3-1試片清洗 31
3-3-2成長LaNiO3薄膜 32
3-3-3成長BiFeO3摻Ca薄膜 32
3-3-4成長AZO薄膜 32
3-4實驗分析儀器 36
3-4-1 X光反射儀(X-ray Reflectivity, XRR) 36
3-4-2 X光繞射儀(X-ray Diffraction, XRD) 38
3-4-3 場發射掃描式電子顯微鏡(Field-emission Scanning Electron Microscope，FE-SEM) 43
3-4-4原子力顯微鏡(Atomic Force Microscopy, AFM) 44
3-4-5 IV與光伏量測 44
3-4-5 TF2000 鐵電薄膜量測儀 45
3-4-6 反射式紫外/可見吸收光譜儀(UV/VIS/NIR Spectrophotometer) 46
第四章 結果與討論 49
4.1 摻雜與未摻雜比較 49
4.2 XRD (X-ray diffraction) 56
4.3 XRR (X-ray reflectivity) 59
4.4 表面形貌分析AFM分析 63
4.5 微觀結構(SEM) 67
4.6 光學測量 70
4.6電滯曲線 71
4.7 漏電流與電阻測量 72
4.8 光伏測量 74
4.9 綜合因素比較 80
第五章 結論 86
參考文獻 86



















圖目錄
圖2-1 (A) 原始狀態 (B) 極化狀態 (C) 極化後狀態 6
圖2-2 極化頻率 8
圖2-3 極化機制 9
圖2-4 BiFeO3結構圖 13
圖2-5 Rhombohedral and hexagonal unit cell in a lattice 14
圖2-6電滯曲線 15
圖2-7 極化量與電場關係圖 16
圖2-8 時間響應度對光電流與開路電壓的影響 19
圖2-9 照光強度對光電流與開路電壓的影響 20
圖2-10 I-V curve 21
圖2-11 Doping ratio與C (Å)比較 21
圖3-1 濺鍍示意圖 28
圖3-2 RF magnetron sputtering system 29
圖3-3 磁控濺鍍系統示意圖 30
圖3-4清洗流程圖 31
圖3-5成長流程圖 33
圖3-6成長BiFeO3薄膜測量 34
圖3-7成長AZO薄膜測量 34
圖3-8元件結構圖 35
圖3-9 二環繞射儀器圖 36
圖3-10 Snell's law 示意圖 38
圖3-11 布拉格定律示意圖 40
圖3-12 Θ-2Θ掃描模式示意圖 41
圖3-13 Rocking curve掃描模式示意圖 42
圖3-14 X光機外觀 42
圖3-15 X光機內部圖 43
圖3-16 KEITHLEY 2400量測儀器圖 44
圖3-17 TF-2000鐵電測量儀 45
圖3-18 全光譜圖 46
圖3-19反射式紫外光-可見光吸收光譜儀器圖 48
圖4-1 BFO:Ca & pure BFO XRD圖 51
圖4-2 BFO:Ca & pure BFO ROCKING CURVE圖 51
圖4-3 BFO:Ca & pure BFO SEM與AFM圖 52
圖4-4 BFO:Ca & pure BFO 穿透光譜圖 52
圖4-5 BFO:Ca & pure BFO 反射光譜圖 53
圖4-6 BFO:Ca & pure BFO 電滯曲線圖 53
圖4-7 BFO:Ca & pure BFO 漏電流圖 54
圖4-8 BFO:Ca & pure BFO I-V曲線圖 54
圖4-9 BFO:Ca & pure BFO時間響應圖 55
圖4-10 LNO/BFO:Ca在不同厚度下之X光繞射圖 56
圖4-11 LNO/BFO:Ca在(100)下的搖擺曲線圖 57
圖4-12 LNO/BFO:Ca在(200)下的搖擺曲線圖 57
圖4-13 LNO/BFO:Ca/AZO的X光繞射圖 58
圖4-15 LNO/BFO:Ca反射率Fitting圖 62
(a) 25 nm (b) 50 nm (c) 75 nm (d) 100 nm (e) 150 nm 62
圖4-16 LNO/BFO:Ca & pure BFO AFM圖 66
(a) 25 nm (b) 50 nm (c) 75 nm (d) 100 nm (e) 150 nm 66
圖4-17 LNO 50 nm+BFO:Ca 25 nm SEM圖 67
圖4-18 LNO 50 nm+BFO:Ca 50 nm SEM圖 67
圖4-19 LNO 50 nm+BFO:Ca 75 nm SEM圖 68
圖4-20 LNO 50 nm+BFO:Ca 100 nm SEM圖 68
圖4-21 LNO 50 nm+BFO:Ca 150 nm SEM圖 69
圖4-22 BFO:Ca 穿透光譜圖 70
圖4-23 BFO:Ca 反射光譜圖 70
圖4-24 BFO:Ca 電滯曲線圖 71
圖4-25 LNO/BFO:Ca/AZO 漏電流圖 72
圖4-26 LNO/BFO:Ca電阻對厚度圖 73
圖4-27 LNO/BFO: Ca/AZO I-V曲線圖 74
圖4-28 LNO/BFO:Ca/AZO與純BFO VOC & JSC曲線圖 75
圖4-29 LNO/BFO:Ca/AZO 填充因子曲線圖 76
圖4-30 LNO/BFO:Ca /AZO 效率曲線圖 77
圖4-31 LNO/BFO:Ca/AZO 時間響應圖 78
圖4-32 不同厚度對電阻&極化值&光電流&效率關係圖 79
表目錄

表1-1鐵電材料表 4
表4-1 BFO:Ca & pure BFO VOC & JSC &填充因子&效率&電阻 55
表4-2 LNO/BFO:Ca 角度與半高波寬 58
表4-3 LNO/BFO:Ca反射率Fitting結果 60
表4-4 LNO/BFO:Ca粗糙度 63
表4-5 LNO/BFO:Ca/AZO Voc & Jsc &填充因子 76
表4-6 LNO/BFO:Ca/AZO 效率 77

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