INTERFACE STRUCTURE OF GAN ON SAPPHIRE(0001) STUDIED BY TRANSMISSION ELECTRON-MICROSCOPE

Structural defects of GaN grown by plasma-assisted molecular beam epit axy on sapphire (0 0 0 1) substrates have been studied by transmission electron microscope (TEM). Cubic GaN (c-GaN) islands, surrounded by h exagonal GaN (h-GaN), with the typical height and width of 6 and 50 nm , respectively, were observed in the vicinity of the substrate by sele cted area diffraction pattern and high-resolution image. The epitaxial relationship between c-GaN and h-GaN was determined as h-GaN (0 0 0 1 ) parallel to c-GaN (1 1 1), h-GaN(1 o -1 1) parallel to c-GaN (1 0 0) and h-GaNC[1 1 -2 0] parallel to c-GaN [1 1 0]. Because the boundary between c-GaN and h-GaN has high density of dislocations, the mixed cu bic-hexagonal character near the substrate may play an important role in the relaxation of large misfit stress created by lattice mismatchin g between GaN and sapphire substrate. (C) 1998 Elsevier Science B.V. A ll rights reserved.