Reconstructions of the $\mathrm{GaN}\left(000\overline{1}\right)$ surface are studied for the first time. Using scanning tunneling microscopy and reflection high-energy electron diffraction, four primary structures are observed: $1\times 1,3\times 3,6\times 6$, and $c(6\times 12)$. On the basis of first-principles calculations, the $1\times 1$ structure is shown to consist of a Ga monolayer bonded to a N-terminated GaN bilayer. From a combination of experiment and theory, it is argued that the $3\times 3$ structure is an adatom-on-adlayer structure with one additional Ga atom per $3\times 3$ unit cell.

• Received 20 June 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.3934