Growth of GaN layers onto misoriented (0001) sapphire by metalorganic chemical vapor deposition

The growth process of GaN layers grown by metalorganic chemical vapor deposition on sapphire is characterized by transmission electron microscopy and atomic force microscopy. The nitridation of the sapphire substrate and GaN buffer layers as well as film structure and the nature of defects are studied. Nitridation causes the formation of a 4 nm thick AlN layer on sapphire. GaN buffer layers grown at 510 degrees C are found to be hexagonal single crystals in their as-grown state with a mosaic structure. Annealing of the buffer layers leads to substantial smoothening of their surfaces due to the coalescence of the grains. GaN layers themselves are single crystalline, hexagonal, and epitaxial to the substrate. Layers grown on exactly oriented (0001) type substrate as well as on miscut substrate are compared. Smooth surfaces have been achieved on exactly oriented and on miscut substrates as well, but the range of the deposition parameters is wider when miscut substrates are used. (C) 1999 American Institute of Physics. [S0021-8979(99)03123-0].