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. Nface reconstructions are primarily adatom-on-adlayer structures which can be formed by room temperature sub-monolayer 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.