STM study of controlling heteroepitaxial growth of nitride semiconductor films on an atomic scale

A number of reconstructures of the GaN(0001) surface have been investigated systematically in situ by reflection high-energy electron diffraction and scanning tunneling microscopy. The GaN thin films were grown on the Si-term inated 6H-SiC(0001) surface by N plasma-assisted molecular beam epitaxy und er the Ga-rich conditions. While the as-grown GaN surface is revealed to be a featureless 1 x 1 structure, post-grown deposition of Ga at lower temper atures results in the formation of the series of ordered superstructures, s uch as 2 x 2, 4 x 4, 5 x 5, 5 root3 x 2 root 13, root7 x root7, and 10 x 10 in the order of the increasing Ga-coverage and annealing temperature. An 1 x 1-Ga-fluid structure is obtained with the highest Ga-coverage. Neither o rdered structure nor smooth morphology has been observed under the N-rich r egime. We conclude that the atomic structures of all these Ga-rich phases c an be described best by a Ga-adatom scheme.