LHPG晶纖生長方法之空間微非對稱性模擬分析

Simulation and Analysis of LHPG Crystalline Fiber Growth under Asymmetrical Perturbations

陳平夷(P. Y. Chen) ； 黃恩萍(E. P. Huang) ； 羅家堯(C. Y. Lo)

《鑛冶：中國鑛冶工程學會會刊》 56卷4期 (2012/12) Pp. 101-110

https://doi.org/10.30069/MM.201212.0011

摘要

在對稱的條件下，微浮動熔區流場呈現對稱雙渦流分佈，然而當擾動增加時，雙渦度流場會由對稱到傾斜，最後流場震盪呈現不穩定。我們的目的是藉由探討雷射加熱基座法（laser-heated pedestal growth, LHPG）生長晶纖時，在架設原棒與籽晶於基座位置上，所發生的軸向微量偏移而造成之空間擾動，致使熔區重力場與二氧化碳雷射加熱環偏斜，對熔區形狀（固液與氣液介面）與流場分佈造成影響。進而探討水平LHPG微浮動熔區晶體生長的可行性。兩種偏移之影響，在經由釔鋁石榴石（Yttrium Aluminum Garnet, YAG）材料以不同縮徑比、原棒尺度、表面張力、熱毛係數評估分析後，加熱環偏移明顯影響固液介面形狀與熔區內部流場之對稱性。只要加熱環盡可能對稱條件下，較大之重力場偏移對熔區影響是有限的。因此在材料物性與原棒尺度許可條件下，水平LHPG微浮動熔區晶體生長是可行的。三維非對稱模擬系統架構是加入縮徑與加熱的條件，修改Lan的熱毛細流熔區程式，其數值方法是應用有限體積法，其網格並經體適網格轉換。為了提升模擬的仿真度與呈現更真實的物理涵義，均先行完成熔區形狀與實驗比對。在經驗上，空間擾動約可控制在3度範圍。直徑為500微米，縮徑比0.5為基準，比對縮徑比降至0.25與原棒尺度降至300微米的熔區內流場分佈。最後我們也以原棒直徑為1000微米，重力場垂直於晶體生長方向時，模擬LHPG水平生長之方式，進一步讓我們評估與分析。

關鍵字

熱傳 ； 流場 ； 雷射加熱基座法 ； 單晶成長 ； 釔鋁石榴石

並列摘要

When under symmetrical conditions, microfloating zone showed symmetrical double eddy flow field. However, when perturbation increased, the double eddy flow field became skewed and finally unstable flow field. This study investigated the influence of molten zone on shape (vapor-liquid and solid-liquid interfaces) and internal heat flow field caused by the tilting of CO2 laser heating ring and gravity field in LHPG crystalline fiber growth system.A three-dimensional simulator was used to simulate LHPG crystalline fiber growth system. The simulator incorporated the conditions of diameter reduction ratio and laser heating, and Lan's thermocapillary floating numerical mode. We compared the molten zone shape depicted by the simulator and that from the experiment. The simulation result showed that the double eddy flow field presented tilt in x-y plane at z=0. The flow field vector and equipotential lines of the vertical and horizontal flow field were no longer symmetry at the central axial of the molten zone. The flow field mainly was affected by the laser heating ring deviation and the influence decreased with the source rod scale and diameter reduction ratio. The influence of gravity to the flow field was negligible. We also simulated the growth axis and the gravity field perpendicular to each other under 1000-μm-diameter source rod. When the surface tension is lowered (~ 500 dyn cm^(-1)) vapor-liquid interface drooped in the direction of gravity field, leading to tilt in the solid-liquid interface. Appropriate heating ring with reverse angle compensation enabled the solid-liquid interface to maintain symmetry, and helped developing LHPG crystal fiber growth with good crystal quality along horizontal direction.

並列關鍵字

A1. Heat transfer ； A1. Fluid flows ； A2 ； Laser heated pedestal growth ； A2 ； Single crystal growth ； B1. Yttrium compounds