On the kinetics of growth of highly defective GaN epilayers and the origin of the deep trap responsible for yellow-band luminescence

The kinetics of growth of GaN/(0001) sapphire heteroepitaxial films have been examined in the relatively low substrate temperature range, 560-640 degrees C, using the reflection high energy electron diffraction (RHEED) specular reflection intensity monitoring technique. In particular, an alternate element exposure method of growth was employed in which Ga and N atoms were supplied separately (rather than simultaneously, as in conventional molecular beam epitaxy) to the substrate with the inclusion of a time delay between successive Ga flux and N flux exposures. We interpret the observed time dependent recovery of the RHEED specular reflection intensity during the time delay phases to be associated with Ga-N surface molecule migration on Ga-terminated surfaces and the activation energy for this migration process was determined to be 1.45+/-0.25 eV. (C) 1997 American Institute of Physics.