Growth and Surface Reconstructions of AlN(0001) Films

The growth and surface reconstructions of AlN(0001) films were studied. For moderately Alrich surfaces, the 2×6 structure is commonly observed in reflection high energy electron diffraction. It is found that this pattern consists of 2√3×2√3-R30° and 5√3×5√3-R30° reconstructions according to scanning tunneling microscopy. Similar to the Ga-rich GaN(0001) surface, these structures are determined to contain 2−3 monolayers of excess Al terminating the surface. Based on first-principles theory the structures are believed to contain a laterally contracted Al layer. At higher Al coverage a thick, flat Al film is found to form on the surface. A high density of growth spirals (associated with threading dislocations having full or partial screw character) is found to be present on the surface, although this density decreases with increasing growth temperature.