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 epitax y. N-face reconstructions are primarily adatom-on-adlayer structures w hich can be formed by room temperature submonolayer Ga deposition. The se structures undergo reversible order-disorder phase transitions to 1 X1 in the temperature range of 200-300 degrees C. Ga-face reconstructi ons, on the other hand, require annealing to high temperatures (600-70 0 degrees C) in order to form, and in most cases they are stable at th ose temperatures. The film polarity is found to be determined by the i nitial nucleation stage of the film growth. (C) 1998 American Vacuum S ociety.