Thick AlGaN layers and AlGaN/GaN superlattices have been grown on GaN using metalorganic chemical vapor deposition. Cross-sectional transmission electron microscopy has been used to show that V-shaped surface pits on these samples differ from similar features observed in the InGaN system. Inversion domains and segregated Al are found in the middle of each V pit, and superlattice layers are observed to follow the pit sidewalls.

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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°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 ͑0001͒ 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.

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