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提出新的生长控制方式“函数控制方法”并将其应用到HVPE异质外延GaN中。函数控制方法是指外延生长参数随时间按照特定函数变化来实现生长控制的方式。采用函数控制方法设计了两个实验方案,解决了HVPE获得GaN衬底面临的两个主要问题。1)异质外延高质量无裂纹GaN厚膜的实验方案:生长条件按照渐变函数变化保证了外延材料质量的稳定性和应力释放的均匀性,生长条件按照周期函数变化将材料的厚膜外延问题转化为薄膜外延问题。2)GaN厚膜的自分离实验方案:生长条件按照跃变函数变化实现了在外延材料特定位置形成弱连接层,生长条件按照渐变函数变化实现了弱连接层两侧出现较大应力差,这种应力差在生长结束后的降温过程中得到进一步放大,进而实现外延材料在弱连接层处的自分离。结合以上两个实验方案,成功获得无色透明表面平整光滑1 mm厚的高质量GaN衬底,证明了函数控制方法的有效性。借助于生长参数规律化的函数变化,函数控制方法建立了材料性质和数学函数之间的对应和联系,丰富和发展了材料的生长控制方式。
Proposed a new growth control method “function control method ” and applied it to HVPE heteroepitaxial GaN. Function control method refers to the growth of epitaxial growth parameters over time according to a specific function to achieve growth control. Two control schemes were designed by using the function control method, which solved two main problems faced by HVPE for obtaining GaN substrate. 1) High-quality heteroepitaxy crack-free GaN thick film experimental scheme: growth conditions in accordance with changes in the gradient function to ensure the stability of the quality of the epitaxial material and stress release uniformity, growth conditions according to the periodic function of the thick film epitaxial material problems Transferred to the film epitaxial problems. 2) Self-isolation experiment scheme of GaN thick film: According to the change of growth function, the weak connection layer is formed at a specific position of the epitaxial material according to the change of the growth function. According to the change of the gradient function, the larger stress difference appears on both sides of the weak connection layer The stress difference is further amplified during the cooling process after the end of growth, so as to realize the self-separation of the epitaxial material at the weak connection layer. Combined with the above two experimental schemes, a high quality GaN substrate with a smooth and smooth surface of 1 mm in thickness was successfully obtained, which proves the effectiveness of the function control method. By means of the function change of the law of growth parameter, the function control method establishes the correspondence between the material property and the mathematical function, and enriches and develops the growth control mode of the material.