Molecular beam epitaxial growth and scanning tunneling microscopy studies of the gallium rich trench line structure on N-polar w-GaN(0001¯)

In addition to the usual set of the well-known reconstructions that have been observed on the N-polar GaN surface, namely 1 × 1, 3 × 3, 6 × 6, and c(6 × 12), an additional structure is occasionally seen at high Ga coverage, which can extend over a large area of the surface. This structure, which is referred to as trench line structure, is partially ordered and consists of parallel-running dark (trench) lines separating wide and narrow strips of atomically ordered regions. There are also randomly placed defects interrupting the ideal ordering. Reflection high energy electron diffraction and scanning tunneling microscopy in ultrahigh vacuum are applied to investigate this trench line structure on samples prepared using molecular beam epitaxy. It is found that the trench line structure results from annealing the Ga-rich c(6 × 12) at high temperature followed by quenching to room temperature. By careful comparison of the scanning tunneling microscopy images with those from neighboring c(6 × 12) regions, it is...