Wurtzite GaN surface structures studied by scanning tunneling microscopy and reflection high energy electron diffraction

We report studies of the surface reconstructions for both the Ga-face and the N-face of wurtzite GaN films grown using molecular beam epitaxy. N-face reconstructions are primarily adatom-on-adlayer structures which can be formed by room temperature submonolayer Ga deposition. These structures undergo reversible order–disorder phase transitions to $1×1$ in the temperature range of 200–300 °C. Ga-face reconstructions, on the other hand, require annealing to high temperatures (600–700 °C) in order to form, and in most cases they are stable at those temperatures. The film polarity is found to be determined by the initial nucleation stage of the film growth.