利用溶膠-凝膠法製備Na摻雜奈米ZnO薄膜並探討其結構、光學與電性質

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研究生：	吳尚軒 Shang-Hsuan Wu
論文名稱：	利用溶膠-凝膠法製備Na摻雜奈米ZnO薄膜並探討其結構、光學與電性質 Investigations on Structural, Optical and Electrical Properties of Na Doped ZnO Nanocrystalline Thin Films Using Sol-Gel Process
指導教授：	鄭偉鈞 Wei-Chun Cheng 任盛源 Shien-Uang Jen
口試委員:	尚格偉 Thangavel Rajalingam
學位類別：	碩士 Master
系所名稱：	工程學院 - 機械工程系 Department of Mechanical Engineering
論文出版年：	2012
畢業學年度：	100
語文別：	英文
論文頁數：	63
中文關鍵詞：	鈉摻雜奈米氧化鋅薄膜、溶膠凝膠法、拉曼光譜、光致螢光
外文關鍵詞：	Na doped ZnO nanocrystalline thin films, sol-gel method, Raman spectra, photoluminescence
相關次數：	點閱：345 下載：4
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本實驗使用溶膠-凝膠法於藍寶石（0001）基板上製備不同濃度鈉掺雜氧化鋅薄膜，並且於空氣及氬-氫混和氣氛下退火以獲得鈉掺雜之氧化鋅薄膜。所有的樣品皆利用X-ray繞射光譜、掃描式電子顯微鏡、原子力顯微鏡、光致螢光光譜、穿透光譜、拉曼光譜、X-ray光電子能譜儀以及霍爾效應測量儀檢測，以瞭解不同濃度之鈉掺雜在結構、光學與電性上的影響。
XRD結果證實所有的樣品皆為六方晶系纖鋅礦結構，同時具有沿c軸成長的擇優取向；其（002）面的半高寬隨著掺雜濃度增加至3莫耳%而減少；表面形貌的觀察和粗糙度的計算將透過SEM及AFM來進行，結果顯示隨著掺雜濃度增加會使得表面粗糙度上升。純氧化鋅薄膜其PL顯示於3.269 eV具有強烈的紫外線放射並伴隨一微弱之綠光放射，此綠光放射主要源於內部氧空缺的缺陷放光；隨著鈉掺雜濃度增加導致了能隙寬度的增加進而使得光譜於紫外線波段出現藍位移的現象，而近能隙邊緣的光致螢光下降是由於導帶被自由載子填滿所致；同時光譜具有微弱的近紅外線放射，此微弱的近紅線放射是由於施體-受體間轉換與氧間隙能階捕捉淺層電子造成。另外，鈉掺雜氧化鋅薄膜之透光率可藉由穿透光譜測得，結果顯示利用掺雜鈉之氧化鋅薄膜，可提升於可見光波段之穿透率。
拉曼光譜中隨著Na_Zn^+取代鋅原子位置，但由於原子半徑差導致了張應力的產生使得E2（high）訊號的波數往較低波數的方向移動，另外，在具有多重聲子的拉曼光譜中，藉由掺雜鈉有助於提升縱向光學聲子(A1(LO))之訊號並可觀察到五重的多重聲子訊號。X-ray光電子能譜儀可用來驗證實際掺雜之濃度。霍爾效應量測結果顯示濃度為1 莫耳%之鈉掺雜為p型氧化鋅薄膜，載子濃度為1.69×10^16 cm^-3，載子遷移率 3.34 及電阻率 1.11×10^2 Ω-cm。

In the present work undoped and Na-doped zinc oxide (ZnO) thin ﬁlms have been deposited on sapphire (0001) substrates using sol-gel method. In order to obtain the high quality thin films, the samples were preheated at 250 ℃ for 10 min and annealed in air and Ar/H2 (95%/5%) at 500 ℃ for 1 h. The grown thin films were analyzed in the X-ray diffraction (XRD), scanning electron microscopy (SEM), Atomic force microscopy (AFM), photoluminescence (PL), transmittance spectrum, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Hall measurements.
The XRD analysis reveals that the undoped and Na-doped thin films have grown in the form of hexagonal Wurtzite structure with high c-axis preferred orientation. The FWHM of (002) peak decreases as the Na-doped concentration increases to 3 mol%. Surface morphology of the films was analyzed using SEM and AFM, which showed the sodium dopant would induce the surface roughness increase. The PL spectra of ZnO showed a strong ultraviolet (UV) emission band located at 3.269 eV, and a weak visible emission associated with the singly ionized oxygen vacancy. Sodium incorporation induced a blue shift of optical band gap and quenching of the near-band-edge PL for thin film because of the band-filling effect of free carriers. Besides, the near-infrared (NIR) emission peak (1.64 eV) can be observed as well, which is ascribed to the radiative recombination of shallowly trapped electrons with deeply trapped hole at Oi and the donor-acceptor transition between VO and VZn. Transmittance spectra were confirmed that Na-doped ZnO can enhance its transmittance in the visible wavelength range.
In micro- Raman Scattering for Na-doped ZnO film, the decrease in the E2 (low) phonon wavenumber is observed. It is ascribed to increase the Na_Zn^+ substitution to Zn site and decrease in the E2 (high) phonon wavenumber due to Na-doped induced tensile stress. A strong enhancement of multiple-phonon Raman scattering process with longitudinal optical phonon (A1(LO)) overtone up to fifth order was observed. XPS analysis was used to ensure the experimental doping concentration. The electrical properties of 1 mol% Na-doped ZnO thin film is p-type with hole carrier concentration 1.69×10^16 cm^-3, mobility 3.34 cm^2/Vs and resistivity 1.11×10^2 Ω-cm.

Abstract (in Chinese) I
Abstract (in English) III
Acknowledgement V
Contents VII
Figure and Table Lists X
Chapter 1 Introduction 1
1-1 Fundamental Properties of ZnO 1
1-1-1 Crystal structure of ZnO 2
1-1-2 Optoelectronic characteristics of ZnO 5
1-2 Growth techniques of ZnO 6
1-3 Applications of ZnO 7
1-4 Background and Motivation	7
1-5 Organization 9
Chapter 2 Theory and Measurement Systems	10
2-1  Growth of ZnO thin films using sol-gel method 	10
2-1-1 Introduction 10
2-1-2 Principle of spin coating 11
2-1-3 Drying and annealing 11
2-2  Characterization techniques 13
2-2-1 X-ray diffraction (XRD) 13
2-2-2 Scanning electron microscope (SEM)	15
2-2-3 Atomic force microscopy (AFM) 17
2-2-4 2-2-5 Raman spectroscopy	19
2-2-5 Photoluminescence (PL) spectrum 21
2-2-6 Hall effect measurement 22
2-2-7 Transmittance measurement 23
2-2-8 X-ray photoelectron spectroscopy (XPS) 24
Chapter 3 Materials and Methods 26
3-1  Experimental procedure 26
3-1-1 Chemistry of the precursor solution and sols 26
3-1-2 The substrate cleaning 28
3-1-3 The fabrication of ZnO/NZO thin films 29
3-2  Instruments 31
3-2-1 Preparation of sol-gel solutions 31
3-2-2 Spin coater 31
3-2-3 Furnace 32
3-2-4 X-ray diffraction 33
3-2-5 Scanning electron microscope 33
3-2-6 Atomic force microscopy 34
3-2-7 Micro-Raman and micro-PL microscopy	 34
3-2-8 Hall effect measurement 35
3-2-9 Transmittance measurement 35
3-2-10 X-ray photoelectron spectroscopy 36
Chapter 4 Results and Discussion 37
4-1  The doping effect of structural characteristics 37
4-2  Surface morphology 39
4-2-1 Scanning electron microscope (SEM) 39
4-2-2 Atomic force microscopy (AFM) 43
4-3  Optical properties 46
4-3-1 Photoluminescence (PL) spectrum 46
4-3-2 Transmittance spectrum 48
4-3-3 Raman spectrum 49
4-4  X-ray photoelectron spectroscopy (XPS) 52
4-5  Electrical properties 55
Chapter 5 Conclusion 57
References 60

                                

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