用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.

Observation of Dislocation Etch Pits in GaN Epilayers by Atomic Force Microscopy and Scanning Electron Microscopy

A combination of atomic force microscopy (AFM) and scanning electron microscopy (SEM) is used to characterize dislocation etch pits in Si-doped GaN epilayer etched by molten KOH.Three types of etch pits with different shapes and specific positions in the surface have been observed,and a model of the etching mechanism is proposed to explain their origins.The pure screw dislocation is easily etched along the steps that the dislocation terminates.Consequently a small Ga-polar plane is formed to prevent further vertical etching,resulting in an etch pit shaped like an inverted truncated hexagonal pyramid at the terminal chiasma of two surface steps.However,the pure edge dislocation is easily etched along the dislocation line,inducing an etch pit of inverted hexagonal pyramid aligned with the surface step.The polarity is found to play an important role in the etching process of GaN.