Microstructure And Origin Of Dislocation Etch Pits In Gan Epilayers Grown By Metal Organic Chemical Vapor Deposition

Morphology and microstructure of dislocation etch pits in GaN epilayers etched by molten KOH have been investigated by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). Three types of etch pits (alpha, beta, and gamma) are observed. The alpha type etch pit shows an inversed trapezoidal shape, the beta one has a triangular shape, and the gamma type one has a combination of triangular and trapezoidal shapes. TEM observation shows that alpha, beta, and gamma types etch pits originate from screw, edge, and mixed-type threading dislocations (TDs), respectively. For the screw-type TD, it is easily etched along the steps that the dislocation terminates, and consequently, a small Ga-polar plane is formed to prevent further vertical etching. For the edge-type TD, it is easily etched along the dislocation line. Since the mixed-type TDs have both screw and edge components, the gamma type etch pit has a combination of alpha and beta type shapes. It is also found that the chemical stabilization of Ga-polar surface plays an important role in the formation of various types of dislocation etch pits.