HVPE异质外延GaN的函数控制方法研究

Function Control Method for GaN Heteroepitaxy by HVPE

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。

A new growth control way,Function Control Method,is introduced in GaN heteroepitaxy by hydride vapor phase epitaxy（HVPE）.Function Control Method is a growth control way in which growth parameters vary as certain mathematical functions of time.Two growth schemes are designed by the aid of this method to solve two main problems confronted in obtaining free-standing GaN substrates by HVPE.In the heteroepitaxial growth scheme of crack-free high-quality thick film,growth parameters’ variations as gradual functions of time ensure that the growing of high-quality GaN maintains sustainable advantage while the strain is being released gradually.Besides,the periodic functions turn the problem of thick-film heteroepitaxy into an easy one of thin-film heteroepitaxy.In the separation scheme of the thick epilayer,growth parameters’ twice sharp transitions produce a weakly connected thin interlayer.Also,except for the twice sharp transitions,growth parameters’ variations as gradual functions of time bring about stress difference between two sides of the weakly connected thin interlayer.The stress difference can be further intensified during the cooling process,leading to the thick epilayer’s self-separation at the weakly connected thin interlayer.With the combination of the two schemes,1 mm-thick transparent GaN crystal with a smooth surface was obtained,which proved the effectiveness of Function Control Method.Relying on growth parameters’ regular orderly change over time,this method develops new ways of material growth control,and links properties of the growing material with the mathematical functions according to which growth parameters vary.