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-terminated 6H-SiC(0001) surface by N plasma-assisted molecular beam epitaxy under the Ga-rich conditions. While the as-grown GaN surface is revealed to be a featureless 1 × 1 structure, post-grown deposition of Ga at lower temperatures results in the formation of the series of ordered superstructures, such as 2 × 2, 4 × 4, 5 × 5, 5√3 × 2√13, √7 × √7, and 10 × 10 in the order of the increasing Ga-coverage and annealing temperature. An 1 × 1-Ga-fluid structure is obtained with the highest Ga-coverage. Neither ordered structure nor smooth morphology has been observed under the N-rich regime. We conclude that the atomic structures of all these Ga-rich phases can be described best by a Ga-adatom scheme.