Interface structure of GaN on sapphire (0 0 0 1) studied by transmission electron microscope

Abstract

Structural defects of GaN grown by plasma-assisted molecular beam epitaxy on sapphire (0001) substrates have been studied by transmission electron microscope (TEM). Cubic GaN (c-GaN) islands, surrounded by hexagonal GaN (h-GaN), with the typical height and width of 6 and 50nm, respectively, were observed in the vicinity of the substrate by selected area diffraction pattern and high-resolution image. The epitaxial relationship between c-GaN and h-GaN was determined as h-GaN (0001)‖c-GaN (111), h-GaN(10−11)‖c-GaN (100) and h-GaN[11−20]‖c-GaN [110]. Because the boundary between c-GaN and h-GaN has high density of dislocations, the mixed cubic-hexagonal character near the substrate may play an important role in the relaxation of large misfit stress created by lattice mismatching between GaN and sapphire substrate.