Epitaxy of Al films on GaN studied by reflection high-energy electron diffraction and atomic force microscopy

Epitaxy of Al films deposited on GaN has been studied using reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), x-ray diffraction, and ion channeling techniques. Al (111) films have been found to grow epitaxially on GaN (0001) surfaces with Al <[2(11)over bar]>parallel to GaN<[2(11)over bar 0]>. For growth at 15 and 150 degrees C with a deposition rate of 0.26 Angstrom/s, the epitaxial quality of the film was poor initially, as evidenced by the observation of diffuse RHEED patterns. After a few monolayers, a sharp and streaky RHEED pattern develops and is maintained during subsequent deposition, indicating an improvement in epitaxial quality with a two-dimensional growth mode. AFM studies indicate that the initial GaN surface quality is a significant factor in achieving epitaxial growth, and that the size of Al epitaxial islands increases substantially for higher growth temperatures. X-ray diffraction and ion channeling results confirm the epitaxial nature of the Al films in spite of a significant lattice mismatch of 10.2%. (C) 1997 American Institute of Physics.