利用界面相本征电动势原位探测晶体生长界面波动和形态的研究

The in-situ detection of growth interface melt convection, which is the connection between interface state and corresponding control means, could improve the crystal quality. Since even in an ideal temperature field, the baroclinic instability generated from intrinsic coupled convections will oscillate the growth interface by hydrothermal waves. This phenomenon could generate crystallographic defects as well. However, current convection control methods hardly reflect the convection variation, which even results in the increase of interface fluctuation. Therefore, to reveal and control the state of growth interface, the means to detect and analyze melt convection in situ plays the major role. We have proved the direct relationship between the fluctuation of output power, convection, crystal rotation and the electromotive force of growth interface (GEMF) by the growth striations distribution. Then, on the basis of our previous work, firstly, we aim to obtain the time evolution of convections from the basic parameters of the melt. And then, using the in-situ GEMF spectrum, we can reveal the response of GEMF to the crystallization and supercooling phenomena. Besides, the accelerated crystal rotation technique (ACRT) would be used to control the melt convection. Finally, combining the in-situ GEMF detection and the ACRT, we could build a closed loop convection control system to realize the dynamic suppression of interface fluctuation and the adjustment of interface shape. The outcomes of our project will offer the significant evidence to reveal the convection instability mechanism, and is the strong guarantee of developing striation-free and high-quality large size synthetic crystals as well.

原位探测人工晶体生长界面熔体对流波动，是界面状态与其调控手段的桥梁，对提高晶体品质有决定性作用。即使温场理想，熔体对流耦合作用导致的斜压不稳定现象，仍会在生长界面产生轴向热流体波造成晶体缺陷。然而现有对流调控手段难以实时获取对流变化，甚至反使界面波动激增。因此，如何在极端敏感严苛的生长界面中探测和解析熔体对流，是揭示和调控界面状态的关键。申请人已利用晶体生长条纹分布规律证实功率、对流和晶转波动与界面相本征电动势的紧密关联。在此基础上，拟从熔体参数出发，获取界面对流的含时演化规律；再结合原位探测的电动势谱，揭示其对结晶和过冷度的响应机理，以定量表达界面的时相关波动轨迹；进而依据轨迹规划晶体变速旋转，以调控对流规律；最终组建具备对流状态原位反馈能力的闭环控制系统，实现界面波动动态抑制和界面形态闭环调控。项目成果是解析熔体本征对流失稳机理的重要依据，也是研制缺陷可控的大尺寸高品质晶体的有力保障。

在提拉法晶体生长系统中，固液生长界面是制备晶体的核心区域，其波动和形态能左右晶体品质；同时也是“不可见”区域，其产生的条纹、变形、温度起伏等复杂现象始终难以在漫长的晶体生长过程中实时展现，致使缺乏规避缺陷增殖、应力积累、组分不均等破坏性现象的有效手段，严重局限了体块人工单晶的品质和性能。.本项目围绕“利用界面相本征电动势原位探测晶体生长界面波动和形态”，通过对晶体固液相界面的电动势的分析，原位探测由强迫-自然耦合对流引发的界面热波动，并基于探测结果调控晶体生长参数，抑制界面波动和反馈界面形状。在理论方面，应用全局温场仿真、非稳态流体力学数值计算、和边界层近似模型，分析本征电动势的构成、界面波动现象的起源、和质热输运的动力学过程。在实验工作中，通过拆解熔滞回线、分析时间序列、和建立塞贝克基线，归纳瞬时生长速度与电动势的关系，并计算界面相变的能量积累。最终一方面通过准确预测“生长条纹梯度分布”规律，验证结晶与过冷度电动势与生长速度的数值关系；另一方面通过准确判定“生长界面形状”，验证相变动力学与质热输运分析结果。.值得一提的是，综合理论分析与实验结果，本项目提出了一套对人工晶体工业生产极富价值的工艺优化方案和过程分析方法。例如，建立生长界面闭环控制系统：基于耦合熔体对流波动规律，反馈控制晶体非定常旋转，实现界面波动的动态抑制；基于电动势与温度的时间序列互关分析，在温度边界层模型中描绘相变动力学轨迹，实现对界面形状的实时精准预测，并以之反馈控制界面形状演化过程。项目的研究成果提供了原位揭示提拉法熔体本征对流失稳机理的重要依据，并能辅助晶体产业研制缺陷可控的大尺寸、高品质人工晶体。