  The reconstructions of the Ga polarity GaN(0 0 0 1) surface with and without
trace amounts of arsenic and prepared by molecular beam epitaxy (MBE) have been
studied with in situ reflection high-energy electron diffraction (RHEED) and
scanning tunneling microscopy (STM). Various reconstructions are observed with
RHEED by analyzing patterns while the substrate is exposed to a fixed NH3 flux
or after depositing known amounts of Ga as a function of substrate temperature.
In situ STM images reveal that only a few of these reconstructions yield
long-range periodicity in real space. The controversial role of arsenic on Ga
induced reconstructions was also investigated using two independent MBE
chambers and X-ray photoelectron spectroscopy.
