Morphology of GaN(0001) and GaN(0001) surfaces: Persistence of surface clusters

We report a scanning tunneling microscopy and low energy electron diffraction study of GaN(0001) and GaN(0001̄) surfaces. Surface preparation methods included anneal, N2+ sputter/anneal, and chemical etching with Br2. The onset of surface facet formation by thermal anneal is 1050 K, determined by electron diffraction, whereas the onset of facet formation by Br2 etching at elevated sample temperatures is 765 K. For all surfaces studied, facetted and unfacetted, nanosize clusters are observed in scanning tunneling microscopy images regardless of treatment. The presence and persistence of these clusters is discussed, as well as their potential impact on studies of GaN surface chemistry and surface electronic structure.