https://scholars.lib.ntu.edu.tw/handle/123456789/62958
標題: | 加速坩堝旋轉對垂直布氏法晶體生長偏析及界面的影響: 可視化實驗及數值模擬 Effect of accelerated crucible rotation on segregation and interface morphology for vertical Bridgman crystal growth: visualization and simulation |
作者: | 劉有晟 Liu, Yu-Cheng |
關鍵字: | 垂直布氏法;偏析;加速坩堝旋轉;界面;vertical Bridgman;segregation;accelerated crucible rotation;interface morphology | 公開日期: | 2007 | 摘要: | 使用垂直布氏法生長晶體時,晶體中添加物濃度的均勻性相當重要,然而在固化過程中自然對流造成局部偏析嚴重影響晶體添加物的濃度,此為難以避免的情況。加速坩堝旋轉技術 (Accelerated Crucible Rotation Technique, ACRT) 以及角振動技術 (Angular Vibration Technique, AVT) 皆同樣是以加速坩堝旋轉的方式改變垂直布氏法熔湯的流動。在許多文獻當中,對於ACRT同一週期中加速及減速的熔湯流動機制並沒有深入的探討,而AVT 是本實驗室這兩年提出的新方法,並沒有太多的文獻。故本論文中不但會討論琥珀腈(succinonitrile) 在添加輕溶質丙酮(acetone)及重溶質柳酸苯酯(salol)時,垂直固化的界面形態差異,更進一步討論到不同強度的ACRT以及AVT對界面形態的影響。藉由電腦數值模擬的結果來分析比較,不論是界面形狀、熔湯流動方向、濃度分布皆合理地與實驗結果相符。同樣就改善偏析的目的來看,使用ACRT 會增進軸向及徑向熔湯的混合,也造成界面較大的變形,而使用AVT則能夠局部增進徑向溶質的混合,也能得到較平整的界面,在晶體生長的觀點上AVT的優點略多於ACRT。 In vertical Bridgman (VB) crystal growth process, the solute uniformity of obtained crystal is very important but however segregation due to buoyancy force during binary solidification which affects dopant concentration severely is always inevitable. Accelerated crucible rotation technique (ACRT) and angular vibration technique (AVT) are both kind of accelerated crucible rotation, and the purpose of them is to vary melt flow field in during VB crystal growth. In several studies, the mechanism of ACRT in detail is not very clearly addressed, especially the interplay of spin-up and spin-down flow in one ACRT cycle. AVT is a novel method which was proposed and demonstrated by our group in these two years, so there are rare literatures concerning this subject. In this study, both of lighter (acetone) and heavier (salol) solute are added in succinonitrile (SCN) sample to observe how different dopant affects interface morphology during directional solidification. The effect of different intensity ACRT and AVT on interface morphology is also investigated for these two samples. By the implement of numerical simulation, interface morphology, flow intensity and direction, and concentration field give very good agreement with experimental observation. To modify the condition of segregation, ACRT enhances radial and global mixing of solute in the meanwhile and compensates with larger concavity of interface. AVT enhances only radial mixing of solute, and more planar interface can be obtained. In view of crystal growth, comparison of ACRT and AVT results establishes AVT to be superior scheme for VB crystal growth in terms of segregation control and interface morphology. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/52340 | 其他識別: | en-US |
顯示於: | 化學工程學系 |
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ntu-96-R94524077-1.pdf | 23.53 kB | Adobe PDF | 檢視/開啟 |
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