Structural, optical and sensing characteristics of ZnO nanorods grown on different substrates.

本論文主要在藍寶石基板成長氧化鋅晶種層，並利用濕蝕刻晶種層形成擇區成長氧化鋅奈米柱之結構。同時也使用玻璃基板及P 型矽基板，以水熱法(Hydrothermal method)在不同成長時間(30-90 min)和不同醋酸鋅溶液濃度(0.01-0.04 M)下成長氧化鋅奈米柱，並鍍上厚度為350 nm的指叉狀鋁電極，形成金屬-半導體-金屬的氣體感應器及光檢測器。 由SEM圖可以看出在藍寶石基板及P 型矽基板上成長的氧化鋅奈米柱密度和成長方向有明顯的差異，且皆以成長時間為60 min及醋酸鋅濃度為0.03 M的奈米柱在單位面積下有最大的表面積。由X光繞射分析儀(X-ray Diffractometer, XRD)及光激發螢光(Photoluminescence, PL)分析可得知氧化鋅奈米柱的成長時間為60 min和醋酸鋅溶液為0.04 M時有最強的峰值及紫外光強度，和SEM分析出的總體積及總表面積有關。 氣體感應器之量測溫度為50–300 °C及感應氣體濃度為50–2000 ppm，結果表明各種成長參數所製備出之感應器皆在300 °C及氣體濃度為2000 ppm的環境下有最高的電阻響應值。這是因為成長時間為60 min及醋酸鋅濃度為0.03 M所製備的奈米柱在單位面積上具有最大的總表面積，此結果使此氣體感應器有最好的感應特性。比較以玻璃和藍寶石基板所製備的奈米柱，可發現前者具有較高的電阻響應值，在300 °C和2000 ppm的H2及CO可測到1.91及1.85的響應值，但後者反應時間和回復時間比較快，在相同條件下的H2及CO的反應時間分別為80 s及115 s。量測氣體感應器在空氣中的穩定性可發現，到第六天電阻響應值會降低25 %；而在氬氣中的穩定性可延長到第三十天，電阻響應值才會降低20 %。 紫外光檢測器的量測顯示，電阻比值會隨著醋酸鋅濃度增加而降低，在藍寶石基板上以醋酸鋅濃度0.01 M及成長60 min之奈米柱製備的光檢測器，可測得最高的電阻比值。In this study, wet etching was used to produce patterned ZnO seed layer arrays, then the ZnO nanorods were grown by hydrothermal method. The different growth times (30-90 min) and concentrations of zinc acetate solution (0.01-0.04 M) were performed to grow ZnO nanorods, then the thermal evaporation method was used to deposit 350 nm-thick Al interdigitated electrodes as M-S-M gas sensors and UV light detectors. From the SEM analysis, there were significant differences between the ZnO nanorods grown on different substracts. The maximum surface area of the ZnO nanorod was found with zinc acetate solution of 0.03 M and growth time of 60 min. The XRD analysis shows that the ZnO seed layer and the nanorods are typical wurtzite structures with preferred orientation along the (002) plane. The sample prepared with zinc acetate solution of 0.04 M and growth time of 60 min achieved the highest (002) peak intensity from XRD analysis and the highest UV light intensity from PL measurement. The highest responses were obtained as the ZnO nanorods grown for 60 min with zinc acetate solution of 0.03 M on glass and sapphire substrates because of their large total surface area. The gas sensing response increased with the increasing measurement temperature or gas concentration, and the highest sensing response of the devices on different substrates were obtained under the temperature of 300 °C and the gas concentration of 2000 ppm regardless of H2 and CO gas. The highest gas sensing responses of 1.91 and 1.85 for H2 and CO were found at the concentration of 2000 ppm on glass substrates. The shortest response times of 80 s and 115 s for H2 and CO were found at the concentration of 2000 ppm on sapphire substrates. Stability test of sensors shows significant decrement (20-25% ) of the gas sensing responses after 30 and 6 days in Ar and air atmospheres, respectively. For ZnO nanorods as UV light detectors, the photo response decreased with the increase of the concentration of zinc acetate solution. The highest response of 15 was found on the ZnO nanorods grown for 60 min with zinc acetate solution of 0.01 M on sapphire substrates.誌謝 i 摘要 ii Abstract iii 目錄 iv 第一章 緒論 1 1.1 前言 1 1.2 研究動機與目的 2 第二章 文獻回顧與基礎理論 4 2.1 氧化鋅晶體結構與特性 4 2.2 氧化鋅光學特性 6 2.3 氧化鋅的成長機制 8 2.4 溶膠-凝膠法(Sol-Gel Method) 11 2.5 溶膠-凝膠的製備方法 12 2.6 氧化鋅在氣體感應器的應用 13 2.7氧化鋅在光檢測器的應用 19 第三章 實驗流程與步驟 21 3.1 實驗流程 21 3.1.1 實驗流程圖 21 3.1.2 氧化鋅奈米柱陣列製作示意圖 22 3.2 化學藥品與實驗用品 23 3.2.1 化學藥品 23 3.2.2 基板介紹 23 3.3 實驗儀器介紹 25 3.3.1 熱蒸鍍機 25 3.3.2 X光繞射儀分析 26 3.3.3 FE-SEM場發射掃描電子顯微鏡 27 3.3.4光激發螢光分析儀 28 3.4 基板清洗 29 3.5 氧化鋅晶種層製備 30 3.5.1氧化鋅溶膠製備 30 3.5.2氧化鋅種子層製備 31 3.5.3濕蝕刻處理 32 3.5.4退火處理 33 3.6 水熱法成長氧化鋅奈米柱陣列 34 3.7 熱蒸鍍機鍍鋁電極 35 3.8 紫外光檢測器量測 36 3.9 氣體感應器量測 37 第四章 結果與討論 39 4.1無圖案化之氧化鋅種子層與奈米柱陣列之形貌與晶體分析 39 4.1.1 氧化鋅種子層XRD分析 39 4.1.2 氧化鋅晶種層SEM分析 40 4.1.3 無圖案化之氧化鋅奈米柱陣列XRD分析 40 4.1.4 無圖案化之氧化鋅奈米柱陣列SEM分析 41 4.1.5 氧無圖案化之氧化鋅奈米柱陣列室溫螢光光譜 47 4.2圖案化之氧化鋅種子層與奈米柱陣列之形貌與晶體分析 50 4.2.1 氧化鋅凹點陣列晶種層XRD分析 50 4.2.2 氧化鋅凹點陣列晶種層SEM分析 52 4.2.3 圖案化之凹點陣列化氧化鋅奈米柱陣列XRD分析 53 4.2.4 圖案化之凹點陣列化氧化鋅奈米柱陣列SEM分析 55 4.2.5 圖案化之凹點陣列化氧化鋅奈米柱陣列室溫螢光光譜 59 4.3氣體感應器量測及分析 62 4.3.1 不同溫度之量測 62 4.3.2 不同氣體濃度之量測 73 4.3.3不同成長濃度之量測 76 4.3.4動態分析 78 4.3.5均勻性分析 82 4.3.6穩定性分析 88 4.4光感應器量測及分析 92 第五章 結論 94 參考文獻 9