垂直温度梯度凝固法(VGF)制备InP晶体的固液界面稳定性及孪晶的形成和调控机理研究

Indium phosphide (InP) is an important compound semiconductor material. InP substrate of single crystal is basically monopolized by developed countries such as the United States, France and Japan. Vertical Gradient Freeze (VGF) is an optimizing method to fabricate InP crystals with low defect. Because it is very easy to form twins and other defects during InP crystal growth by the VGF method, and the suppression of twins and the control of dislocation multiplication are a pair of contradictions, the yield of InP single crystal with low defect is very low. Hence, this project firstly studies the transport and distribution of solute in the front of solid-liquid interface by calculating the thermodynamic properties of doped melts. Then the interfacial stability of the solid - liquid interface and three phase interface of the solid - liquid - crucible wall is further studied under low temperature gradient. Through comparative experiments, the influence of facets, temperature gradient, growth rate and location dislocation distribution on the formation of twins at the three phase zone is studied. Then based on the dynamics of facet growth and two-dimensional nucleation, the nucleation model of the twins at the three phase zone will be built. By studying the growth conditions, segregation of doped elements and thermal stress during crystal growth, the project will reveal the formation mechanism of low-angle boundaries and twins forming in low-angle boundaries zone. Finally, by optimizing the crystal growth experiment of the VGF method and combining statistical process control method (SPC), the regulatory mechanism between twins and micro-defects will be obtained. The successful implementation of this project has a positive scientific significance for the development of InP single crystal with low defect density in China.

磷化铟(InP)是一种重要的化合物半导体材料。InP单晶衬底基本被美、法、日等发达国家垄断。垂直温度梯度凝固技术(VGF)是制备低缺陷晶体的优选方法。由于VGF生长InP晶体时极易形成孪晶等缺陷，且孪晶的抑制与位错增殖的控制是一对矛盾，因此高品质InP成晶率非常低。鉴于此，本项目首先研究掺杂熔体的热力学性质，获得固液前沿溶质传输行为及低温度梯度下固-液界面及固-液-坩埚壁三相交界区的界面稳定性规律。通过对比实验，探索研究三相交界区小平面特征、温度梯度、生长速率及局部位错分布等对孪晶形成的影响；基于小平面生长动力学及二维形核动力学，建立InP孪晶形核模型。通过研究生长条件，宏观偏析及生长热应力等因素揭示小角晶界及其区域内孪晶的形成机制。最终通过优化VGF实验及结合统计过程控制（SPC）方法获得孪晶与微观缺陷的调控机理。该项目成功实施对于提升我国低缺陷InP单晶的发展具有积极的科学意义。

本项目研究了VGF和LEC法生长单晶过程中三相交接界面的小平面特征及孪晶形貌，利用并进行了不同放肩角度晶体生长，进而分析了孪晶的形核和小平面与粗糙界面的转化情况。基于实验结果，提出了三相交接界面的几何构造和微观生长机制，揭示三相点界面的迁移过程及动力学平衡规律，通过孪晶和小平面生长的动力学研究，获得孪晶形核模型，该模型也解释了具有沟槽结构的孪晶形核现象。通过磷化铟晶体中的位错形核规律研究，结合形核机理突破，获得了磷化铟制备中的孪晶与位错的调控机制。本项目通过优化热场来增加温度场的对称性，避免了小角晶界和沟槽孪晶的形成，显著降低了VGF晶体生长过程中的孪晶几率。基于孪晶形核机理，发明了多晶合成与VGF结合的新型生长方法，用于制备高纯、超低缺陷晶体，解决了本领域关键共性难题。通过对该方法的优化和相关机理研究，获得了防止熔体倒吸的动力学判据，进而突破了20公斤级别的大容量合成技术。基于孪晶与位错的调控机制，制备出6英寸磷化铟单晶，位错密度降至实用化水平。本项目研究为制备高品质磷化铟单晶、提高晶体的成晶率提供理论和工艺基础，具有重要的理论和应用意义。