| 摘要: | 在本論文中，建立了一個三維數值模型，用以分析採用邊界限定薄膜供料生長法（Edge-Defined Film-Fed Growth，EFG）生長 β-Ga?O? 晶體過程中的溫度場與熱誘發應力. 該模型是在穩態條件下建立, 並考慮了晶體沿 [010] 生長方向的各向異性熱導率, 同時假設結晶界面為平面. 透過電磁模擬獲得 EFG 系統內部的熱源分佈, 從而研究電磁加熱、溫度場以及晶體內熱應力形成之間的關係.
模擬結果顯示, 熱量主要在坩堝壁處產生, 並透過熱傳導與輻射傳遞至熔體與晶體, 進而形成軸向與徑向溫度梯度. 這些溫度梯度是熱應力產生的主要原因, 其中等效 von Mises 應力主要集中於靠近生長界面的晶體邊緣區域. 結果亦表明, 內部輻射對晶體內部的溫度分佈具有顯著影響, 而熔體流場對生長界面處的熱條件則未產生明顯影響.
此外, 本研究探討了在坩堝上方設置防護遮罩以改善熱傳條件並降低熱應力的效果. 結果顯示. 安裝遮罩可提高晶種區域的溫度, 減小軸向溫度梯度, 從而顯著降低熱應力. 進一步分析了晶體在生長過程中長度變化的影響, 結果顯示, 隨著晶體逐漸伸出高溫區, 溫度梯度與熱應力均呈現增加的趨勢.
總體而言, 本研究闡明了 EFG 法生長 β-Ga?O? 晶體過程中熱應力形成的機制, 並為優化系統設計與操作條件、降低熱應力及提升晶體品質提供了科學依據.
;In this thesis, a three-dimensional numerical model is developed to analyze the thermal field and thermally induced stress during the growth of β-Ga?O? crystals using the Edge-Defined Film-Fed Growth (EFG) method. The model is established under steady-state conditions and takes into account the anisotropic thermal conductivity of the crystal along the [010] growth direction, while the crystallization interface is assumed to be planar. The heat source distribution within the EFG system is obtained through electromagnetic simulations, allowing the relationship between electromagnetic heating, the thermal field, and thermal stress formation in the crystal to be examined.
The simulation results show that heat is mainly generated at the crucible walls and transferred to the melt and the crystal through conduction and radiation, resulting in axial and radial temperature gradients. These temperature gradients are the primary cause of thermal stress, with the von Mises equivalent stress mainly concentrated near the crystal edges close to the growth interface. The results also indicate that internal radiation has a significant influence on the temperature distribution within the crystal, whereas the melt flow field has no noticeable effect on the thermal conditions at the growth interface.
In addition, the effect of a protective shield placed above the crucible is investigated to improve heat transfer conditions and reduce thermal stress. The results demonstrate that the installation of the shield increases the temperature in the seed region, reduces the axial temperature gradient, and consequently leads to a significant reduction in thermal stress. Furthermore, the influence of crystal length during the growth process is examined, showing that as the crystal extends out of the hot zone, both temperature gradients and thermal stress tend to increase.
Overall, this study provides insight into the mechanisms of thermal stress formation in β-Ga?O? crystals grown by the EFG method and offers a scientific basis for optimizing system design and operating conditions to reduce thermal stress and improve crystal quality. |
