Reconstructions of GaN(0001) and (0001) surfaces: Ga-rich metallic structures

Reconstructions of GaN(0001) and (<000(1)over bar>) surfaces are studied by scanning tunneling microscopy and spectroscopy, by electron diffraction, by Auger electron spectroscopy, and using first-principles theory. Attention is focused on Ga-rich reconstructions for each surface, which are found to have a metallic character involving significant overlap between Ga valence electrons. The electron counting rule is thus violated for these surfaces, but they nonetheless form minimum energy structures. (C) 1998 American Vacuum Society.