Growth of high-quality gallium nitride films on a silicon carbide surface

Thin films of GaN(0001) have been grown on 6H-SiC(0001) substrates by molecular beam epitaxy combined with processing under a nitrogen plasma. The silicon carbide surface was cleaned by a novel two-step method including high-temperature processing in hydrogen and etching in a silicon flux under conditions of an ultrahigh vacuum. Observation of the 6H-SiC(0001) surface morphology in a scanning tunneling microscope has revealed large flat terraces separated by upright steps. Depending on the Si-flux intensity and the specimen temperature, (3×3) or (√3 × √3) reconstructions have been revealed. The atomic-resolution STM-image of a Ga-rich GaN(0001) surface has confirmed the presence of the terrace-step structure over the entire scanning area and permitted us to observe directly a series of superstructures with the (2×2), (4×4), (5×5), and (7×7) symmetry, as well as individual defects surrounded with aggregated screw dislocations.