MICROSTRUCTURE OF GAN EPITAXY ON SIC USING ALN BUFFER LAYERS

The crystalline structure of GaN epilayers on (0001) SiC substrates ha s been studied using x-ray diffraction and transmission microscopy. Th e films were grown by metalorganic chemical vapor deposition, using A1 N buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmiss ion electron lattice images show that the ALN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structur e of the GaN film away from the substrate consists mostly of threading dislocations with a density of similar to 10(9) cm(-2). (C) 1995 Amer ican Institute of Physics.