Intrinsic Surface Reconstructions of Zinc-Blende GaN(001) Studied by Scanning Tunneling Microscopy*

The intrinsic structures of semiconductor surfaces are important for epitaxial growth and future applications. Here we present a scanning tunneling microscopy study of the clean zinc-blende GaN(001) surface, free from the presence of arsenic. We find a sequence of reconstructions for the clean surface, beginning with 4x3 and including c(4x12), 4x7, c(4x16), 4x9, and c(4x20). Generally, all of these reconstructions are row-like. The 4x3 is a semiconducting surface structure with a bandgap, measured using tunneling spectroscopy, of 1.14 eV; the 4x3 is obtained under Ga-poor surface conditions and is compared with a model calculated using ab-initio techniques. The other reconstructions are metallic, obtained under Ga-rich surface conditions. They can be modeled using simple adatom schemes on top of a bulk-like Ga atom termination.